High Pressure vs. Low Pressure Tank Question...
Cliff Seeley
I am considering purchasing a steel 120 and have two options, high and
low pressure. Can someone please explain to me the difference (other
than the obvious)?!!! I have asked three dive shops and gotten three
different asnwers. My opinion (for what it's worth) is that 120 cubic
ft of air is 120 cubic ft of air and the pressure just determines the
size of the cyliner it's fitting into. My bottom time should be the
same either way, right???? PLEASE, somebody tell me!!!!
Perry West
Cliff Seeley (see...@si.com) wrote:
: I am considering purchasing a steel 120 and have two options, high and
You're right -- 120 cu ft = 120 cu ft. (of course tank capacity is not
precisely equal to the size designation, so there may be some slight
difference). Not only with the amount of air be the same in the tank,
but the weight of the air will be the same. However, the weight and size
of the empty tank (and the full tank) will be different. The high
pressure tank will be smaller and, I believe, lighter. Bouyancy change
from full to empty will be different with the high pressure tanks
changing bouyancy less due to their smaller displacement. You will
likely have different yoke fittings for the two tanks; although, you can
put a DIN fitting onto the low pressure tanks if you want.
For local diving, the high pressure tank would be my personal
preferance. For dive travel, there are other issues. Most dive boats
that supply tanks use tanks with the conventional yoke fitting. If your
regulator has a DIN fitting, you will need to bring an adaptor or change
your regulator for the trip. If the boat does not supply tanks, it is
very likely they cannot fill to 3500 psi; you will get a 3000 psi
filling and proportionally less air. You may also have to bring an
adaptor (if one is available) to allow the boat to fill a tank with a
DIN fitting.
BTW, in Europe you can get tanks rated to 4000 psi and, I believe,
higher. In the U.S., the maximum pressure tank that can be transported
is 3500 psi. So, in the U.S., don't have a tank with a pressure over
3500 psi because 1) you can't legally take it to the dive site, and 2)
dive shops are not equipped to fill to the higher pressure.
Regards,
Perry
Tom Rettie
Perry West wrote:
> Cliff Seeley (see...@si.com) wrote:
> : I am considering purchasing a steel 120 and have two options, high and
> : low pressure. Can someone please explain to me the difference (other
> : than the obvious)?!!!
>
> You're right -- 120 cu ft = 120 cu ft. (of course tank capacity is not
> precisely equal to the size designation, so there may be some slight
> difference).
Some other differences:
High pressure tanks tend to be more prone to internal corrosion (at
least from my own experience and a number of divers I know). Don't be
too surprised if you end up rolling your HP steels every year or two.
Getting complete high pressure fills can be problematic. It's much
easier to get a complete 2260 psi fill than a complete 3500 psi fill
(not many dive shops are that patient).
Weight and buoyancy vary by mfgr, but in general a heavier tank is not
necessarily a bad thing, if it lets you drop some lead off your belt.
Hope that helps,
Tom R.
mol
Cliff Seeley wrote:
>
> I am considering purchasing a steel 120 and have two options, high and
> low pressure. Can someone please explain to me the difference (other
> different asnwers. My opinion (for what it's worth) is that 120 cubic
> ft of air is 120 cubic ft of air and the pressure just determines the
> size of the cyliner it's fitting into. My bottom time should be the
> same either way, right???? PLEASE, somebody tell me!!!!
Aloha,
Isn't one tank smaller and lighter than the other? Even though they
have the same capacity.
The valve fittings are different (DIN vs yolk type), filling a tank
requires an adaptor for older compressors.
Will you be doing most of your diving where you live?
I, for one, would go for the high pressure if I could get it filled to
capacity where I live (Maui, Hawaii).
For the most part dive shops here hesitate at filling the high
pressure tanks as it is rough on their compressors. At least this was
the case a few years ago when I was pricing high pressure systems.
Dive safe and dive often....
Tim Kern
tk...@maui.net
ham...@evms.enet.dec.com
In article <32c3e9b6...@news.iserv.net>,
see...@si.com (Cliff Seeley) writes:
>I am considering purchasing a steel 120 and have two options, high and
>low pressure. Can someone please explain to me the difference (other
>than the obvious)?!!! ... My opinion (for what it's worth) is that 120 cubic
>ft of air is 120 cubic ft of air and the pressure just determines the
>size of the cyliner it's fitting into. My bottom time should be the
>same either way, right????
Well, not quite. Yes the amount of air is the same, but the size, weight
and buoyancy differences are significant. Here are some representative data.
Product Name Material Capacity Pressure Length Diameter Weight Buoyancy
------------ -------- -------- -------- ------ -------- ------ --------
(CU FT) (PSI) (INCHES) (INCHES) (POUNDS) (POUNDS)
Dolphin Cylinders
DESCENT C120 S 120 2640 28 8.00 45 0
FATHOM S120 S 120 3500 28 7.25 38 1
Sherwood Scuba
SC 0120 S 120 2970 28 8.00 52 -3
ST 0120 S 120 3500 28 7.25 38 1
U.S. Divers
HP3.5 120CU/FT S 120 3500 30 7.25 38 1
(Buoyancy is empty in seawater. This can vary by up to about +/- one pound
from tank to tank.)
As you can see, the HP cylinders are smaller, lighter, and less buoyant.
This means less weight -- two ways: First, the tank itself is lighter.
Second, because it is less buoyant you need less weight on your weight belt.
From the standpoint of weight/buoyancy the HP tanks are superior.
Don't forget that for HP tanks you will need a regulator with a DIN fitting
(or and adapter). This may be and additional cost consideration for you.
(Most present day regulators can be converted, but the parts can cost more
than you might expect.)
--
Charlie Hammond -- Digital Equipment Corporation -- Nashua NH USA
(ham...@peek.enet.dec.com)
All opinions expressed are my own and do not necessarily reflect
my employer's position.
Anker Berg-Sonne
A tiny bit of disinformation in Perry's reponse:
The change in buoyancy after breathing X cubic feet of air from a tank
is EXACTLY the same, regardless the tank material and PSI rating,
namely the weight of the air consumed!
Anker
On Fri, 27 Dec 1996 16:17:04 GMT, pe...@netcom.com (Perry West) wrote:
>Cliff Seeley (see...@si.com) wrote:
>: I am considering purchasing a steel 120 and have two options, high and
>: low pressure. Can someone please explain to me the difference (other
>: than the obvious)?!!! I have asked three dive shops and gotten three
>: different asnwers. My opinion (for what it's worth) is that 120 cubic
>: ft of air is 120 cubic ft of air and the pressure just determines the
>: size of the cyliner it's fitting into. My bottom time should be the
>: same either way, right???? PLEASE, somebody tell me!!!!
>
>You're right -- 120 cu ft = 120 cu ft. (of course tank capacity is not
>precisely equal to the size designation, so there may be some slight
Perry West
Anker Berg-Sonne (an...@ultranet.com) wrote:
: A tiny bit of disinformation in Perry's reponse:
: The change in buoyancy after breathing X cubic feet of air from a tank
: is EXACTLY the same, regardless the tank material and PSI rating,
: namely the weight of the air consumed!
Did you forget about displacement? Which has a greater bouyancy, a
pound of air or a pound of lead? The difference is bouyancy is not due
to weight, but to displacement (volume). Which has greater bouyancy, a
pound of air compressed to 1000 psi, or a pound of air compressed to 2000
psi? Of course, the air at lower pressure has twice the displacement and
is more bouyant.
In considering tanks, high pressure tanks are smaller than the equivalent
low pressure tanks of the same air volume. To put it mathematically (and
simplistically) assume two divers start their dives with tanks of equal
capacity, but one is high pressure and one is low pressure. Assume they
dive until their air is all consumed (don't flame me, this is for
illustration only). Then if:
TL is the weight of the low pressure tank
TH is the weight of the high pressure tank
A is the weight of the air in the filled tanks (equal for both)
VL is the volume (displacement) of the low pressure tank
VH is the volume (displacement) of the high pressure tank
BL is the change in bouyancy for the low pressure tank
BH is the change in bouyancy for the high pressure tank
Then
BL = TL/VL - (TL + A)/VL = -A/VL
BH = TH/VH - (TH + A)/VH = -A/VH
Therefore the difference in bouyancy change is inversely proportional to
the displacement of the tank. The smaller displacement high pressure tank
will have a greater change in bouyancy. (I now realize this contridicts
my statement in the earlier post which was in error. I apologize.) A
more detailed calculation leaving 500 psi in each tank would give
somewhat different results but the same conclusion.
Regards,
Perry
Jason Rogers
Perry,
If I understand your post correctly (which I may not), you fill your
cylinder with seawater at the end of the dive. That's what the
post sounded like...
Do you have a problem with corrosion?
Cheers Jason =:)
Jason Rogers
Sorry Perry,
I had a longer look at your calculations. I was in error with regard
to the seawater stuff...
I see what you're doing now. You've worked out the variation
in the *density* and found that there is a difference. Yep I agree with
that, the bouyancy per unit volume of the two cylinders would be different,
but if you mutiply the bouyancy per unit volume of each cylinder, by
the volume it displaces, you'll find that the volumes cancel out, and
the bouyancy change is soley due to the variation of "A", so that the
two cylinders do indeed change the same amount.
It's like if a big person stands on a scale carrying a 20 kg block, and
a small person stands on a scale, also carrying a 20 kg block, and they
both trow their blocks on the ground, they both loose 20 kg. (but
the percentage weight loss is different, which is what you've worked out)
Cheers Jason =:)
jfmezei
Perry West wrote:
>
> Cliff Seeley (see...@si.com) wrote:
> : I am considering purchasing a steel 120 and have two options, high and
> : low pressure. Can someone please explain to me the difference (other
> : than the obvious)?!!!
120 cu ft is a (US) measure of VOLUME. It is the size of the box.
In such a volume, you can put a variable number of air molecules. The
more molecules you put in, the higher the pressure in the tank will be.
I beleive that you could have the same amount of air in half the tank
size with twice the pressure. To really measure tank capacity, you need
to measure the number of molecules (moles) you can fit at the max rated
pressure of your tank at a particular temperature, and compare that
amount between tanks. Of course, as was stated, there are limits on how
much pressure the dive operators can supply you with.
The difference will be that a physically smaller tank will offer you
less bouyancy when it is empty than a larger tank.
Think of air as a sponge and a tank as a box. The bigger the box, the
more sponges you can fit in. The stronger the box, the more tightly
packed/compressed you can stuff the sponges in.
jfmezei
Anker Berg-Sonne wrote:
> The change in buoyancy after breathing X cubic feet of air from a tank
> is EXACTLY the same, regardless the tank material and PSI rating,
> namely the weight of the air consumed!
Not true.
Bouyancy is a factor of weight AND VOLUME which you displace.
The volume of the tank is fixed. The less air you have in it, the more
bouyant it will be. The more air you have in it, the less bouyant.
Where there is a difference, is in the change in bouyancy which occurs
when you move a couple of molecules of air from a high pressure tank
to a low pressure area in your lungs. If your last breath of air takes
out half of the remaining air in your tank, your tank's bouyancy will
double (half of air remaining in same volume). But when your tank is
full, each breath changes your tank's bouyancy much less.
Similarly, if you have a high pressure (smaller) tank, and a lower
pressure (larger) tank, your tank's bouyancy will change differently
and the smaller tank will always be less bouyant, even when empty.
jfmezei
ham...@evms.enet.dec.com wrote:
> Product Name Material Capacity Pressure Length Diameter Weight Buoyancy
> ------------ -------- -------- -------- ------ -------- ------ --------
> (CU FT) (PSI) (INCHES) (INCHES) (POUNDS) (POUNDS)
>
> Dolphin Cylinders
> DESCENT C120 S 120 2640 28 8.00 45 0
> FATHOM S120 S 120 3500 28 7.25 38 1
Interesting. Same volume, same length, but different diameter !!!!!
I must therefore assume that the shape of the bottle is different, and
that the walls of the 8.0 inches model is much thicker.
Ville Saari
> Bouyancy change from full to empty will be different with the high
> pressure tanks changing bouyancy less due to their smaller displacement.
Wrong. Buoyancy change is the weight of the air taken off the tank and
120 cubic feet of air weights exactly the same no matter how much you
compress it. 4kg or 9lbs. So the buoyancy changes are the same.
Well. Actually the change is exactly the same only if you suck the tank
completely empty. When you leave for example 500psi in it, the amount
of remaining air is not the same. The higher pressure tank has
smaller volume, so 500psi in it is less air than 500psi in low pressure
tank and the usable amount of air is somewhat higher, thus the higher
pressure tank actually has a little bit higher buoyancy change.
--
Ville Saari EMail: v...@iki.fi
Tallbergin puistotie 7 B 21 Phone: +358 9 682 2226
00200 Helsinki
FINLAND /dev/null: write failed, file system is full
Jason
On 27 Dec 1996 21:02:29 GMT, ham...@evms.enet.dec.com () wrote:
>Don't forget that for HP tanks you will need a regulator with a DIN fitting
>(or and adapter). This may be and additional cost consideration for you.
>(Most present day regulators can be converted, but the parts can cost more
>than you might expect.)
Would I be right in thinking from your table that US high pressure
tanks are actually 3500 psi? Because generally in Europe, when people
talk about high pressure tanks, they mean 300 bar (over 4000 psi),
which do require a DIN fitting. Our standard pressure is usually 232
bar (3300 psi) and we use yoke fittings for that. Is it not possible
to get 3300 psi tanks in the US with yoke fittings? And if not, why
not?
Jason
Ville Saari
> Did you forget about displacement? Which has a greater bouyancy, a
> pound of air or a pound of lead? The difference is bouyancy is not due
> to weight, but to displacement (volume).
The buoyancy is the weight of displaced water minus the weight of the tank
and it's contents. The weight of the displaced water is the total volume
of the tank multiplied by water density.
What changes wen you consume the air in the tank? Water density? No.
Tank displacement? No (hopefully). Weight of the tank itself? No.
Weight of the contents of the tank? Yes.
So all that matters, is the weight of the contents of the tank and
a pound of air weighs exactly one pound no matter what kind of a
tank it's in.
> TL is the weight of the low pressure tank
> TH is the weight of the high pressure tank
> A is the weight of the air in the filled tanks (equal for both)
> VL is the volume (displacement) of the low pressure tank
> VH is the volume (displacement) of the high pressure tank
> BL is the change in bouyancy for the low pressure tank
> BH is the change in bouyancy for the high pressure tank
>
> Then
>
> BL = TL/VL - (TL + A)/VL = -A/VL
>
> BH = TH/VH - (TH + A)/VH = -A/VH
Let's try your theory:
We take two tanks, both have the same pressure p:
Tank A: volume VA = 0.5 cubic feet, weight TA = 31lbs
Tank B: volume VB = 500000 cubic feet, weight TB = 31 million lbs
(tank B seems to be a made from pressure hull of a nuclear submarine :-)
Let's call density or air in unit pressure d. Weights of the air in
the tanks are then:
Tank A: AA = VA*p*d = 0.5ft^3*p*d
Tank B: AB = VB*p*d = 500000ft^3*p*d
Now let's calculate the buoyancy changes using your formula:
Tank A: BA = TA/VA-(TA+AA)/VA
= 31lbs/0.5ft^3-(31lbs+0.5ft^3*p*d)/0.5ft^3
= (31lbs-(31lbs+0.5ft^3*p*d))/0.5ft^3
= (-0.5ft^3*p*d)/0.5ft^3
= -p*d
Tank B: BB = TB/VB-(TB+AB)/VB
= 31000000lbs/500000ft^3-(31000000lbs+500000ft^3*p*d)/500000ft^3
= (31000000lbs-(31000000lbs+500000ft^3*p*d))/500000ft^3
= (-500000ft^3*p*d)/500000ft^3
= -p*d
Now can you explain me how is it possible that a million times bigger tank
with million times more air in it can have exactly the same change in
buoyancy? Namely minus pressure mutiplied by density of air in unit pressure,
which means minus density of air in tank pressure.
And how can we measure buoyancy change in units of density instead of units
of force or weight?
Or perhaps your formula was pure bullshit?
Anker Berg-Sonne
The displacement of the tank remains constant all the time since the
tank is basically incompressible. The formulas you provide can't be
right since they deliver the wrong answer. The weight (-buoyancy) of
any object immersed in a liquid is
W=M-V*D
where W is the weight, M is the mass of the object, V is the volume of
the object and D is the mass per unit volume of the liquid. Since V
and D are constants the change in weight is
Wdelta=Wb-Wa=(Mb-V*D)-(Ma-V*D)=Mb-Ma
where Wdelta is the change in weight, Wb is the initial weight, Wa is
the final weight, Mb is the initaial mass and Ma is the final mass.
Since the mass change is solely caused by the mass of the air removed
from the tank we have arrived at the answer I gave before.
As far as the 500psi that was introduced as a later agument and not
relevant to the point made:
CHANGE IN BUOYANCY IS SOLELY THE MASS OF THE AIR BREATHED FROM THE
TANK AND IS COMPLETELY INDEPENDENT OF TANK MATERIAL, TANK CAPACITY,
TANK PRESSURE OR ANY OTHER FACTOR!
Anker
On Sat, 28 Dec 1996 02:20:35 GMT, pe...@netcom.com (Perry West) wrote:
>Anker Berg-Sonne (an...@ultranet.com) wrote:
>: A tiny bit of disinformation in Perry's reponse:
>
>: The change in buoyancy after breathing X cubic feet of air from a tank
>: is EXACTLY the same, regardless the tank material and PSI rating,
>: namely the weight of the air consumed!
>
>Did you forget about displacement? Which has a greater bouyancy, a
>pound of air or a pound of lead? The difference is bouyancy is not due
>to weight, but to displacement (volume). Which has greater bouyancy, a
>pound of air compressed to 1000 psi, or a pound of air compressed to 2000
>psi? Of course, the air at lower pressure has twice the displacement and
>is more bouyant.
>
>In considering tanks, high pressure tanks are smaller than the equivalent
>low pressure tanks of the same air volume. To put it mathematically (and
>simplistically) assume two divers start their dives with tanks of equal
>capacity, but one is high pressure and one is low pressure. Assume they
>dive until their air is all consumed (don't flame me, this is for
>illustration only). Then if:
>
> TL is the weight of the low pressure tank
> TH is the weight of the high pressure tank
> A is the weight of the air in the filled tanks (equal for both)
> VL is the volume (displacement) of the low pressure tank
> VH is the volume (displacement) of the high pressure tank
> BL is the change in bouyancy for the low pressure tank
> BH is the change in bouyancy for the high pressure tank
>
>Then
>
> BL = TL/VL - (TL + A)/VL = -A/VL
>
> BH = TH/VH - (TH + A)/VH = -A/VH
>
Anker Berg-Sonne
The yoke fittings only go up to 3000 PSI, for anything higher you need
DIN fittings in the US.
Anker
On Sat, 28 Dec 1996 15:16:52 GMT, ja...@volnay.demon.co.uk (Jason)
wrote:
forsp...@aol.com
> am considering purchasing a steel 120 and have two options, high and
>low pressure. Can someone please explain to me the difference (other
>than the obvious)?!!! I have asked three dive shops and gotten three
>different asnwers. My opinion (for what it's worth) is that 120 cubic
>ft of air is 120 cubic ft of air and the pressure just determines the
>size of the cyliner it's fitting into. My bottom time should be the
>same either way, right???? PLEASE, somebody tell me!!!!
Several differences. I personally prefer low pressure (2400 or 2650 psi
rated depending on manufacturer ) steel tanks to high pressure (3500 psi
rated) steel for following reasons. I am assuming we are takling about
relativly high volume tanks, range of 94 cu.ft. to 120 cu.ft. capacity.
I'm assuming rated capacities are accurate (they are not) for sake of
illustration only. They are however close enough to be used with
reasonable accuracy.
-High pressure tanks can be hard on your regulator's first stage.
-High pressure tanks require a DIN fitting. Can be a pain if you are doing
multiple dives and not all tanks are DIN. Also can be a problem
getting fills some places. However, there are fairly simple
converters on the market, minimizing the problem.
-Low pressure tanks do tend to be heavier and bulkier (a disadvantage many
feel) but also tend to be more negative at end of dive. Gets some weight
off belt (an advantage I feel, especially here in Northeast). However,
low pressure 120's are REALLY big and heavy. Not so bad at all in
94-112 range.
-I've been told by very knowledgeable equiptment gurus that high pressure
tanks have a much greater tendancy for internal rusting and therefor have
a much shorter ultimate service life. Cannot personally verify this,
but I believe the sources.
-"Pumping" to, lets say 500 psi over rating, low pressure tanks have
distinct advantages. (Yes, I know you're not supposed to do this but it
is quite common). Comparing a high pressure 100 (3500psi rated) to a
low pressure 104 (2400 psi rated):
*High pressure "pumped" is 4000 psi. Really tough on first stage
*Low pressure "pumped" is still "low", 2900 psi
*High pressure 100 psi tank "pumped" is about 115 cu. ft. gas @ 4000
psi
*Low pressure 104 psi tank "pumped" is about 125 cu. ft. gas @ 2900
psi with more "room" if wanted
-Can be hard to get full 3500 psi high pressure fills at air stations
commonly filling to 3000 psi on standard aluminium tanks. Fill high
pressure 100 to 3000 psi, you're
carrying only about 86 cu.ft. gas. No problem to get 2400 or 2650 psi
fill (or even a 3000 "pump"). The whole reason for a high capacity tanks
is to actually carry the extra gas, not just to have a high capacity
tank!
Just a matter of personal preference.
Steve Burke
for...@aol.com
The Wizard
Taking off from the previous thread...
Wrong, most of us are aware that the low-pressure 120 needs to have a
LARGER internal volume than the high-pressure 120 since both will hold the
same amount of one-atmosphere air, compressed by different amounts.
I gather that there is a limitation in the fittings/valves/first-stage
that requires an incompatible DIN valve on the HP tank that my normal reg
won't connect to w/o a converter. So here are my questions:
1) the tank itself: if I saw both a HP and a LP tank in half and measure
their wall thicknesses, what will I find? And are their steel
formulations the same or does the HP use a more advanced alloy?
2) the valve: what is the limitation on the usual valves we use in AL80s?
And what does the DIN-series hardware do to improve on it?
3) what happens if one uses a standard valve in a LP steel tank, but
routinely (illegally) pump it up to 3000 PSI, same as an AL tank? 3000
PSI is "normal" full-tank pressure nowadays; 3500-4000 is "high". So does
the overstuffed LP steel tank present a risk of rupture? Why don't steel
tank makers increase wall thickness 1 mm and rate them to 3000 PSI so we
can use existing regs and get 16% more usable air?
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
The Wizard may be reached at tsc...@tiac.net (home),
or tsc...@draper.com (work), daily from 7 AM to 2 AM.
jfmezei
Ville Saari wrote:
> Wrong. Buoyancy change is the weight of the air taken off the tank and
> 120 cubic feet of air weights exactly the same no matter how much you
> compress it. 4kg or 9lbs. So the buoyancy changes are the same.
Wrong ! 120 cubic feet is the room size. It says nothing about how many
people (molecules of air) you put in it, and says absolutely nothing
about how much it will weigh. (or more precisely how much its mass will
be). You can have the same room size with one person, or 100 persons in
it.
> completely empty. When you leave for example 500psi in it, the amount
> of remaining air is not the same. The higher pressure tank has
> smaller volume, so 500psi in it is less air than 500psi in low pressure
Why are you assuming that the higher pressure tank has lower volume ?
The "high pressure tank" is only a qualifier of how strong the tank
walls
and fittings are so that they can widthstand the bigger forces acting on
the wall by the very compressed interior contents.
jfmezei
Ville Saari wrote:
> What changes wen you consume the air in the tank? Water density? No.
> Tank displacement? No (hopefully). Weight of the tank itself? No.
> Weight of the contents of the tank? Yes.
Correct.
> So all that matters, is the weight of the contents of the tank and
> a pound of air weighs exactly one pound no matter what kind of a
> tank it's in.
NOt perfectly correct. The weight of the water being displaced depends
on the volume of your tank. And that pound/kilo or air in your tank will
occupy a different volume depending on your tank size.
If your tank is physically smaller but allows higher pressures, you will
be able to begin with the same amount of air and your dive will last the
same amount of time. But at the end of your dive, your remaining air
will be contained in a smaller container.
OK, I have just resolved the following which was bugging me:
2 Divers of equal weight and volume and air consumption.
1 is equipped with smaller but higher pressure tank, the other with
larger but lower pressure tank.
Both have the exact same amount of air (weight of air).
The only difference in bouyancy will be the difference in volume of
water being displaced. So the diver with bigger tank will be more
bouyant, thus requiring more weight.
Both divers begin their dive neutrally bouyant. (one with more weights
than the other to compensate for his bigger tank).
Once their tanks are empty (each with 1ATM or pressure), the bigger tank
will be more bouyant than the smaller tank. HOWEVER, that difference in
bouyancy will be the same as the difference when they began their dive
and this same difference will have been compensated with the initial
difference in weights.
The only advantage of a smaller but higher pressure tank would be in its
handling, and lesser resistance in water as you swim. Its disadvantage
would be that it requires more cooling as you fill it up to higher
pressure if you want to really pack the air in. (a tank filled at
3500PSI will have less air in it if it is hot compared to a similar tank
also filled at 3500psi but at colder temperature).
Jim Barteck
Jason wrote:
> Would I be right in thinking from your table that US high pressure
> tanks are actually 3500 psi?
Yes...
Because generally in Europe, when people
> talk about high pressure tanks, they mean 300 bar (over 4000 psi),
> which do require a DIN fitting. Our standard pressure is usually 232
> bar (3300 psi) and we use yoke fittings for that. Is it not possible
> to get 3300 psi tanks in the US with yoke fittings? And if not, why
> not?
In the U.S., tanks up to 3300 psi come from the distributor with K
valves (compact aluminum tanks are rated to 3300, standard aluminums
typically to 3000). 3500 psi tanks come with DIN valves.
I believe this has to do with the pressure rating on the K valve
itself, but since I'm not 100% positive don't quote me on that...
YF,
Jim
http://www.netcom.com/~wtdream/catalog.html
>
> Jason
Jim Barteck
forsp...@aol.com wrote:
> Several differences. I personally prefer low pressure (2400 or 2650 psi
> rated depending on manufacturer ) steel tanks
Just a quick note on the difference between 2400 psi and 2640 psi rated
tanks...
2640 tanks are actually 2400 psi tanks which have received a special
procedure hydrostatic test which allows 10% overfills (2400 + 240 =
2640) through its expiration. Tanks passing this test are designated
with a "+".
Many hydro facilities either can't or won't perform these tests and so
when it comes back from its first hydro 5 years down the road it will
once again be a 2400 psi tank. So if you own one of these tanks, make
sure your hydro facility will give the "+" testing to keep your 2640
rating...
Jason Rogers
Anker said;
The yoke fittings only go up to 3000 PSI, for anything higher you need
DIN fittings in the US.
Anker
Is this the law, or a convention? Here the *standard* size cylinder is
the Aluminium 95 from CIG. They've got yoke valves standard (infact
"DINoid" valves only appeared for them in the last 4-5 years) and they
fill to 3500 psi. (These are the *really* standard, like you find
in hire fleets type cylinder)
There is also a 260 bar (3770 psi) cylinder that has a yoke valve standard.
(BTW, these pressures are used by *everyone* and they don't seem
especially hard on the HP seats)
I tried to get CIG to produce a run of low pressure pony's, but they
wouldn't do it, mainly they said because low pressure cylinders might
be accidentally filled to 3500 psi, which is what "normal" cylinders
fill to.
Cheers Jason =:)
Jason
On 27 Dec 1996 21:02:29 GMT, ham...@evms.enet.dec.com () wrote:
>Don't forget that for HP tanks you will need a regulator with a DIN fitting
>(or and adapter). This may be and additional cost consideration for you.
>(Most present day regulators can be converted, but the parts can cost more
>than you might expect.)
Would I be right in thinking from your table that US high pressure
tanks are actually 3500 psi? Because generally in Europe, when people
talk about high pressure tanks, they mean 300 bar (over 4000 psi),
which do require a DIN fitting. Our standard pressure is usually 232
bar (3300 psi) and we use yoke fittings for that. Is it not possible
to get 3300 psi tanks in the US with yoke fittings? And if not, why
not?
Jason
Anker Berg-Sonne
The yoke fittings only go up to 3000 PSI, for anything higher you need
DIN fittings in the US.
Anker
On Sat, 28 Dec 1996 15:16:52 GMT, ja...@volnay.demon.co.uk (Jason)
wrote:
>On 27 Dec 1996 21:02:29 GMT, ham...@evms.enet.dec.com () wrote:
forsp...@aol.com
> am considering purchasing a steel 120 and have two options, high and
>low pressure. Can someone please explain to me the difference (other
>than the obvious)?!!! I have asked three dive shops and gotten three
>different asnwers. My opinion (for what it's worth) is that 120 cubic
>ft of air is 120 cubic ft of air and the pressure just determines the
>size of the cyliner it's fitting into. My bottom time should be the
>same either way, right???? PLEASE, somebody tell me!!!!
Several differences. I personally prefer low pressure (2400 or 2650 psi
Mike Wallace
On 29 Dec 1996 01:16:01 GMT, ja...@volnay.demon.co.uk (Jason) wrote:
>
>Would I be right in thinking from your table that US high pressure
>tanks are actually 3500 psi? Because generally in Europe, when people
>talk about high pressure tanks, they mean 300 bar (over 4000 psi),
>which do require a DIN fitting. Our standard pressure is usually 232
>bar (3300 psi) and we use yoke fittings for that. Is it not possible
>to get 3300 psi tanks in the US with yoke fittings? And if not, why
>not?
>
>Jason
Jason, I've got a couple of 100cuft aluminimums that are rated to 3300
psi. These are both Luxfer cylinders.
>
========================================
Mike Wallace [\]
Huntsville, Alabama
Just another shitty day in paradise....
34 deg 42' N 86 deg 35' W
========================================
Mike Wallace
On 29 Dec 1996 01:52:37 GMT, an...@ultranet.com (Anker Berg-Sonne)
wrote:
>The yoke fittings only go up to 3000 PSI, for anything higher you need
>DIN fittings in the US.
>
>Anker
My 100's are 3300 psi yoke fitted Luxfers.
diver...@aol.com
In article <32c537b9...@news.demon.co.uk>, ja...@volnay.demon.co.uk
(Jason) writes:
>Would I be right in thinking from your table that US high pressure
>tanks are actually 3500 psi? Because generally in Europe, when people
>talk about high pressure tanks, they mean 300 bar (over 4000 psi),
>which do require a DIN fitting. Our standard pressure is usually 232
>bar (3300 psi) and we use yoke fittings for that. Is it not possible
>to get 3300 psi tanks in the US with yoke fittings? And if not, why
>not?
>
>
Jason
You are correct on the HP tanks in the US. You can get 3300psi AL tanks
generally made by Catalina. They have a larger Diamenter and are quite a
bit heaver. They use the Yoke fitting and not a DIN. Changing from DIN to
yoke is very easy and it is done by screwing on a yoke adaptor by hand, no
tools required. Posidon comes with one for their regulators and Scubapro
and USD also have them as an accessory.
Air weighs .075lb per cuft no matter what pressure it is being filled to.
The difference in buoyancy is different between AL types and also between
the different kinds of steel tanks. Not all steel tanks are made with the
material and therefor have different buoyancy values. I have customers
with HP Genesis who use them every weekend and they look like new when
they are inspected and others that have a surface rust problem inside. I
think that two problems may cause rust. One is where you get your air and
if it is as dry as it is supposed to be and if you keep your tanks in an
area that may have extream cold temparatures causing a moisture to be on
the inside surface from the cold. There is no consistant happening with
the tanks.
In the US for 1997 it is my understanding that Pressed Steel will only be
selling their product to one Dive Manufacture. They will get all of their
HP and LP tanks and no one else will be able to buy from PS. This is
going to be a great opportunity for OMS to increase their tank sales. I
think it is a stupid move but CEO's know everything just like some divers
( I am not talking about Jason this time ).
Have Fun and Safe Diving
Divers Get-Away
Dale City, Va. I-95 Exit 156
Bob Wills
mrl...@totcon.com
On Sat, 28 Dec 1996 18:26:55 -0500, tsc...@tiac.net (The Wizard)
wrote:
>> > (CU FT) (PSI) (INCHES) (INCHES) (POUNDS)
>(POUNDS)
>> >
>> > Dolphin Cylinders
>> > DESCENT C120 S 120 2640 28 8.00 45 0
>> > FATHOM S120 S 120 3500 28 7.25 38 1
>>
>>
>> Interesting. Same volume, same length, but different diameter !!!!!
>>
>> I must therefore assume that the shape of the bottle is different, and
>> that the walls of the 8.0 inches model is much thicker.
>
>Wrong, most of us are aware that the low-pressure 120 needs to have a
>LARGER internal volume than the high-pressure 120 since both will hold the
>same amount of one-atmosphere air, compressed by different amounts.
>
>I gather that there is a limitation in the fittings/valves/first-stage
>that requires an incompatible DIN valve on the HP tank that my normal reg
>won't connect to w/o a converter. So here are my questions:
>
>1) the tank itself: if I saw both a HP and a LP tank in half and measure
>their wall thicknesses, what will I find? And are their steel
>formulations the same or does the HP use a more advanced alloy?
It depends on the manuafature. What good will this info do you. The
biggest thing to worry about is how bouyant it is going to be in the
water.
>
>2) the valve: what is the limitation on the usual valves we use in AL80s?
>And what does the DIN-series hardware do to improve on it?
Stop and think about that one. think of what the usual valves look
like and what a din valve looks like... Which one is better at holding
a "O" ring in ( DIN by all means) . Which has more holding power by
clamping down... Not the usual style. The din is threaded in quite a
bit more than just a (basicaly) bolt. Also the din will let you use a
higher working pressure over the old style.
>3) what happens if one uses a standard valve in a LP steel tank, but
>routinely (illegally) pump it up to 3000 PSI, same as an AL tank?
You will wear out the burst disk, and also the posibility of blowing
yourself and the place that you are filling the tank to kingdom come!!
DON"T do it. You can safely go approx 10% higher on the woking
pressure of a tank. But all shops will usually fill only to the
stamped working pressure.
>PSI is "normal" full-tank pressure nowadays; 3500-4000 is "high". So does
>the overstuffed LP steel tank present a risk of rupture? Why don't steel
>tank makers increase wall thickness 1 mm and rate them to 3000 PSI so we
>can use existing regs and get 16% more usable air?
More Cost to the manufacture, means more cost to us. A tank rated for
3500 - 4000 is not high, and the tank has been tested to that working
pressure before being put on the market!!! If you are wanting more
are for dives, goes to DBBL's.....
>-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
> The Wizard may be reached at tsc...@tiac.net (home),
> or tsc...@draper.com (work), daily from 7 AM to 2 AM.
Lungs
****************************************************
* *
* Mr Lungs *
* mrl...@totcon.com *
* www.totcon.com/users/lungs *
* PADI Divemaster *
* Respiratory Therp *
* A Bad day of Diving, *
* Beats a Good Day at work anytime!! *
* *
****************************************************
LAURENCE CHARLOT
> bar (3300 psi) and we use yoke fittings for that. Is it not possible
> to get 3300 psi tanks in the US with yoke fittings? And if not, why
> not?
> Jason
The only 3300 PSI tank I know of is the 100 cubic foot aluminum
cylinder made by Luxfer. I had one for about a year but sold it
as it's weight and bulk made it too hard to handle. Luxfer's Aluminum 92's
are 3200 PSI ( I own one of these). I think all the "high pressure" steel
cylinders sold by ScubaPro, Sherwood, and US Divers are made by
Pressed Steel Industries and are 3500 PSI with DIN fittings standard.
Beuchat has been marketing a line of European made steel cylinders
(Possibly made in Italy by Faber?) in 95 cu ft, 120 cu ft, and 140 cu ft.
I think these are also 3500 PSI and have DIN valves. The 140 is a real
monster - it weighs something like 80 pounds when full - more than two
Aluminum 80's combined. I heard that in Europe, the Beuchat cylinders
are 4000 psi, but in the US and Canada, they are down-rated to 3500
because of DOT/CTC government regulations.
{lcha...@jps.net}
forsp...@aol.com
In article <32C4D7...@videotron.ca>, jfmezei
<nospam....@videotron.ca> writes:
>To really measure tank capacity, you need
>to measure the number of molecules (moles) you can fit at the max rated
>pressure of your tank at a particular temperature, and compare that
>amount between tanks.
Calculating moles (a mole is 6.02x10 to the 23rd molecules) is an
unnecessarly complex way to measure capacity. Use rated cu.ft. capacity
at rated pressure. Not exact, but a reasonably accurate measure. You can
use simple proportions to estimate actual gas carried in cu.ft. based on
actual tank pressure
>The difference will be that a physically smaller tank will offer you
>less bouyancy when it is empty than a larger tank.
Not at all accurate. Tank construction material, density, content etc
(Archemedies Principle) determine bouyancy of tank. Size per se is of
very little consequence. For example, an aluminum 80 is physically smaller
(by a large margin) than a low pressure steel 120. The aluminum 80 is FAR
more bouyant at end of dive (500 psi). Even more dramatic difference when
tanks are filled to rated capacity. Consult recently posted tank bouyancy
charts for specifics on several tanks of varing size, volume, rated
pressure, and material.
Steve Burke
for...@aol.com
forsp...@aol.com
In article <32C619...@ix.netcom.com>, Jim Barteck
<wtd...@ix.netcom.com> writes:
>Just a quick note on the difference between 2400 psi and 2640 psi rated
>tanks...
> 2640 tanks are actually 2400 psi tanks which have received a
special
>procedure hydrostatic test which allows 10% overfills (2400 + 240 =
>2640) through its expiration. Tanks passing this test are designated
>with a "+".
(balance snipped)
It is my understanding that OMS sells European manufactured (Faber) low
pressure steel tanks with a rated 2650 psi seperate from the "+" rating.
US manufactured Pressed Steel tanks such as I own and are sold for
example by DiveRite, are rated 2400 psi then "+" for added 10%. A minor
point in any event. Can an OMS tank owner confirm? Thanks
Steve Burke
for...@aol.com
diver...@aol.com
>120 cu ft is a (US) measure of VOLUME. It is the size of the box.
> To really measure tank capacity, you need
>to measure the number of molecules (moles) you can fit at the max rated
>pressure of your tank at a particular temperature, and compare that
>amount between tanks.
The size of a tank is measured by water volume per the maunfacture. This
is stated in cubic inches and the approved DOT pressure of fill determins
the air volume.
>In such a volume, you can put a variable number of air molecules. The
>more molecules you put in, the higher the pressure in the tank will be.
>
>I beleive that you could have the same amount of air in half the tank
>size with twice the pressure. Of course, as was stated, there are limits
on how
>much pressure the dive operators can supply you with.
A 80cuft tank rated to 3000PSI filled with 2500psi will contain more air
than a 3500psi tank filled to 2500psi. This occures because the 3500psi
tank will have a smaller water volume than the 300psi tank and therfore
have less air in it.
>
>The difference will be that a physically smaller tank will offer you
>less bouyancy when it is empty than a larger tank.
The material used to make the tank will also effect the buoyancy. That is
just one of the reason fiberglass tank are not used for diving, that are
too buoyant.
>
>Think of air as a sponge and a tank as a box. The bigger the box, the
>more sponges you can fit in. The stronger the box, the more tightly
>packed/compressed you can stuff the sponges in.
This is a good description
Jason Rogers
********
Why are you assuming that the higher pressure tank has lower volume ?
The "high pressure tank" is only a qualifier of how strong the tank
walls
and fittings are so that they can widthstand the bigger forces acting on
the wall by the very compressed interior contents.
*********
Because we were talking about 120 cuft cylinders. If you put 120 cuft
under a pressure of 3000 psi, it takes up half the volume that it does
if you put it under 1500 psi (for example).
A "high" pressure cylinder, will always have a smaller internal volume
than a low pressure cylinder of the same capacity.
Cheers Jason =:)
Carl Heinzl
>>3) what happens if one uses a standard valve in a LP steel tank, but
>>routinely (illegally) pump it up to 3000 PSI, same as an AL tank?
>You will wear out the burst disk, and also the posibility of blowing
#1) - WHAT burst disk... If you don't know what I mean here - go
ask on techdiver.
>yourself and the place that you are filling the tank to kingdom come!!
#2) - You have GOT to be kidding yourself. LP steels are ROUTINELY
pumped up to anywhere from 3000-4000. These things aren't going to
fracture at any rated pressure that any compressor at any dive store can
put out, that's for sure. There are plenty of stores that you take
in your tanks and they simply say "how much" or "how high".
>DON"T do it. You can safely go approx 10% higher on the woking pressure
>of a tank. But all shops will usually fill only to the stamped working
>pressure.
Baloney... I suggest you go to the bank and withdraw a clue - you need
one.
-Carl-
Q. How often do you hydro your tanks?
A. Every time I fill'em.
Kuty
gas...@sydney.DIALix.oz.au (Jason Rogers) wrote:
>Because we were talking about 120 cuft cylinders. If you put 120 cuft
>under a pressure of 3000 psi, it takes up half the volume that it does
>if you put it under 1500 psi (for example).
>A "high" pressure cylinder, will always have a smaller internal volume
>than a low pressure cylinder of the same capacity.
I am lurking in rec.scuba for some time.
I think that I finally got it. Now I also understand why when diving
in the caribbeans, I couldn't get anybody to translate the volume of
the tanks for me.
When you talk about 80 cuft tank, you mean that it holds 80 cuft of
air in 3000 psi. If you fill it with 3500 psi ot turns to be a ~93.33
cuft tank?
What a fucked up system (excuse me). It means that if you talk about
an 80 cuft tank, it will be an 80 only if your filling station filled
it to precisely 3000 psi. The "name" of the tank will change to 70 if
your filling station filled it with only 2625 psi.
Did I get it wrong?
We measure the tanks in litres. But the volume is the internal
volume. You can also say that it holds 12 litres of air in sea level
perssure. If you fill a 12 litres tank with 200 bars (~3000 psi), it
holds twice as much air than if you fill it with 100 bars. It is
still a 12 litres tank. This way, when you buy a tank, or when you
talk about one, you know its size.
Regards,
Kuty
Fred Tagge
Kuty wrote:
> I think that I finally got it. Now I also understand why when diving
> in the caribbeans, I couldn't get anybody to translate the volume of
> the tanks for me.
>
> When you talk about 80 cuft tank, you mean that it holds 80 cuft of
> air in 3000 psi. If you fill it with 3500 psi ot turns to be a ~93.33
> cuft tank?
>
> What a fucked up system (excuse me). It means that if you talk about
> an 80 cuft tank, it will be an 80 only if your filling station filled
> it to precisely 3000 psi. The "name" of the tank will change to 70 if
> your filling station filled it with only 2625 psi.
>
> Did I get it wrong?
You got it right!
> We measure the tanks in litres. But the volume is the internal
> volume. You can also say that it holds 12 litres of air in sea level
> perssure. If you fill a 12 litres tank with 200 bars (~3000 psi), it
> holds twice as much air than if you fill it with 100 bars. It is
> still a 12 litres tank. This way, when you buy a tank, or when you
> talk about one, you know its size.
The liter measurement makes sense. Unfortunately no oone has ever been able to
claim the english/US system of measurement makes any sense. It's a great help
in confusing our enemies on a battlefield, but otherwise has no basis in
logic. But then again neither does our language.
I try to keep track of my tanks by internal cubic inch measurement. For
example a "standard" 72 and a Divequip 3000 have the *same* internal volume.
The 72 is filled to 2250 psi and holds about 69 ft^3 at that pressure. The
3000 has a 3000psi working pressure and holds about 100 ft^3 there. Just a
difference in working pressure
> Regards,
> Kuty
Hugh Huntzinger
Carl Heinzl wrote:
>
> >>3) what happens if one uses a standard valve in a LP steel tank, but
> >>routinely (illegally) pump it up to 3000 PSI, same as an AL tank?
>
> >You will wear out the burst disk, and also the posibility of blowing
>
> #1) - WHAT burst disk... If you don't know what I mean here - go
> ask on techdiver.
Some divers purposefully disable the existing overpressure safety device
in their system. IMO, this is stupid, particularly considering that they
could have instead put a HP burst disk into the LP tank and retained SOME
degree of safety...its chasing an "unseen demon" in Hogarthian terms.
Why? Because burst disks nearly never fail. How many documented cases can be
cited where a properly maintained and properly used disk has actually failed?
(fixing something that's not a problem is "chasing an unseen demon").
> >yourself and the place that you are filling the tank to kingdom come!!
>
> #2) - You have GOT to be kidding yourself. LP steels are ROUTINELY
> pumped up to anywhere from 3000-4000. These things aren't going to
> fracture at any rated pressure that any compressor at any dive store can
> put out, that's for sure. There are plenty of stores that you take
> in your tanks and they simply say "how much" or "how high".
I agree with Carl that there are *SOME* tank designs out there that can safely
accomodate a significantly higher fill than the pressure rating assigned by the
DOT in the USA. HOWEVER, this is brand/model specific and it is not something
that should be done lightly - one needs to do your homework and effectively
"recertify" the tanks to a higher operating pressure yourself.
FWIW, though, any tank failures do tend to be catastrophic events...we had a guy
hurt bad locally when a Scott Pac let loose this summer (it was NOT an overfill).
Overfills are a problem in the "technical" (including cavers) diving community in
that noone has been able to keep the 'paperwork' clean on this issue, so technically
speaking, everyone is a rogue and all information is passed verabally or via the net
or other similar "less than authorotative" means. But good documentation is extremely
appropriate and necessary before one ventures into the realm of exceeding the existing
DOT standards.
One can easily apply a 'Reducto ad Adsurdum' arguement here and conclude that since
Carl's saying that 3000-4000psi is safe, then so is 4,500 and then 5,000 and 6,000
and so forth...UNTIL you reach some pressure where *ALL* tanks fail immediately.
But I don't even think you have to go this far...I'll bet that Carl would NOT feel
particularly comfortable if we asked him to drive some LP tanks 25 miles to a divesite
that were pumped up to "just" 9,000 psi. Oh, yeah: Add hot day and a bumpy road :-).
> >DON"T do it. You can safely go approx 10% higher on the woking pressure
> >of a tank. But all shops will usually fill only to the stamped working
> >pressure.
>
> Baloney... I suggest you go to the bank and withdraw a clue - you need
> one.
Rather, if you happen to know something about:
- Mechanics of Materials; stress & strain
- Fatigue
- Surface finish
- Corrossion
- Deep draw forming
- Non-Ferrous Metallurgy
- Safety Factors
- Manufacturing variability
- Statistical Process Control
- Annealing & Stress Relief processes
...then you're smart enough to go out and getting your BS in Mechanical Engineering,
follow it up with your EIT certification and after a few years of professional practice
and peer references, take your PE (Professional Engineer) licence tests and pass. At this
point, you are NOW finally qualified to recertify the working pressures on that tank.
Otherwise, stay a lot closer to what the manufacturer's recommendations are.
(Note to Carl: this leaves the door open for the "DOT vs the World" issue which I know
that you're basing a lot of your discussion on; I'd rather make that a different thread)
While I have problems with some of the "rules" from "Authorities", IMPO, this rule has
a lot more basis behind it that takes a hell of a lot more research and work to figure
out its hows/whys before one goes breaking it. I'd strongly suggest that you challenge
anyone who tells you its "safe" by asking them to put that down in writing and to sign
their name to it as one who is legally liable if anything bad were to happen. FWIW, I
doubt that you would get many signatures...(BTW, for anyone who disagrees with me,
please include the above-requested legal liability statement in your responses).
> Q. How often do you hydro your tanks?
> A. Every time I fill'em.
This is the classic 'cavers' joke about exceeding rated safetly limits. Granted, they
will be able to get away with such actions for awhile...probably quite awhile...but it
will eventually catch up to them statistically.
These higher pressures completely trash the predicted number of load cycles that were
used for the tank's design analysis, so the tank's overall lifespan will be shortened,
perhaps considerably. The problem is that you no longer have any idea HOW MUCH its been
shortened - it could be only 10,000 fills now or maybe just 1,000 - you just don't know.
Some perspective is necessary and appropriate here - YOU or I may never see 10,000 dives,
but where does your gear go after you've given up diving? It will probably be sold.
There are still a lot of old Steel 72's/68's/65's from the 1960's out there in use.
For AL80's, at a typicl tropical resort, they get a few thousand fills pretty quickly, as
they're used every day. THINK about it.
I did and I decided long ago that my personal ethics were such that I would NEVER expose
another diver to the hazards that exist from me overfilling a tank. Specifically, it means
that I will NEVER SELL a tank which I've overfilled. Instead, I will *DESTROY* that tank.
Why? Because ethically, it became my responsibility to prevent harm from others as soon
as I knowingly exceeded the product's specifications.
YMMV.
-hh
PS: I probably should add some credentials on this one: Former Chairman, Morris-Sussex
Subsection, Region II, American Society of Mechanical Engineers (ASME).
ham...@evms.enet.dec.com
In article <32c5576f...@news.ultranet.com>,
an...@ultranet.com (Anker Berg-Sonne) writes:
>The yoke fittings only go up to 3000 PSI, for anything higher you need
>DIN fittings in the US.
Actually, yokes are rated to 3300 PSI.
--
Charlie Hammond -- Digital Equipment Corporation -- Nashua NH USA
(ham...@peek.enet.dec.com)
All opinions expressed are my own and do not necessarily reflect
my employer's position.
Jason
On 29 Dec 1996 08:01:50 GMT, "LAURENCE CHARLOT" <lcha...@jps.net>
wrote:
>The only 3300 PSI tank I know of is the 100 cubic foot aluminum
>cylinder made by Luxfer. I had one for about a year but sold it
>as it's weight and bulk made it too hard to handle. Luxfer's Aluminum 92's
Yes, you get them over here too, and I agree they are a bit heavy.
>Pressed Steel Industries and are 3500 PSI with DIN fittings standard.
>Beuchat has been marketing a line of European made steel cylinders
>(Possibly made in Italy by Faber?) in 95 cu ft, 120 cu ft, and 140 cu ft.
Well the tank I use is a Faber. I think most of them are over here,
but they're available in Europe in both the 232 bar (3300 psi) and 300
bar (4000 psi) formats. The 300 bar tanks come with DIN fittings and
the 232 ones tend to come with a yoke fitting. The 300 bar tanks are
quite heavy, but the 232 ones aren't too bad.
I think it's quite strange that aluminium tanks are still heavily used
in the US, whereas in Britain they're now relatively rare. I can't
think of anyone I know who uses aluminium tanks.
Jason
diver...@aol.com
In article <5a7s32$o...@news.NetVision.net.il>, ku...@nite.org.il (Kuty)
writes:
>We measure the tanks in litres. But the volume is the internal
>volume. You can also say that it holds 12 litres of air in sea level
>perssure. If you fill a 12 litres tank with 200 bars (~3000 psi), it
>holds twice as much air than if you fill it with 100 bars. It is
>still a 12 litres tank. This way, when you buy a tank, or when you
>talk about one, you know its size.
>Regards,
>Kuty
I checked with one of our distibutors and the US cuft and you Litre rating
are the same principal. This is the amount of air that the tank will hold
when it is filled to its maxium rated pressure. As the pressure decreases
the volumn of air in the tank decreases. While the tanks will always have
their designation remain the same as to capasity the amoun of air inside
will change if it is less or more than the rated fill presure on the tank.
A 12 liter tank is about the same as our 100cuft. I hope this helps.
Once again we are not that different if at all.
Fred Tagge
Hugh Huntzinger wrote:
> Rather, if you happen to know something about:
>
> - Mechanics of Materials; stress & strain
> - Fatigue
> - Surface finish
> - Corrossion
> - Deep draw forming
> - Non-Ferrous Metallurgy
> - Safety Factors
> - Manufacturing variability
> - Statistical Process Control
> - Annealing & Stress Relief processes
>
> ...then you're smart enough to go out and getting your BS in Mechanical Engineering,
> follow it up with your EIT certification and after a few years of professional practice
> and peer references, take your PE (Professional Engineer) licence tests and pass. At this
> point, you are NOW finally qualified to recertify the working pressures on that tank.
Been there, done that, and I won't! At least not for the use of the general public. My neck is
one thing, somebody else's is another thing all together.
> I did and I decided long ago that my personal ethics were such that I would NEVER expose
> another diver to the hazards that exist from me overfilling a tank. Specifically, it means
> that I will NEVER SELL a tank which I've overfilled. Instead, I will *DESTROY* that tank.
BTW The same logic applies to an unsafe and irrepairable firearm. Damage can be due to fire
corrosion, overloading, or manufacturer's defect. The owner should SEE it destroyed with a saw
or torch.
Likewise hydro failed & out of date Caver tanks make nice planters, ash trays, BBQ pits, spare
gasoline tanks, or anything else you can think of, except a pressure vessel.
> Why? Because ethically, it became my responsibility to prevent harm from others as soon
> as I knowingly exceeded the product's specifications.
That attitude can keep a PE out of jail too.;-)
Keeping one's own ethics in is always a wise choice.
Stay wet,
FT
diver...@aol.com
In article <CGH.96De...@martigny.ai.mit.edu>,
c...@martigny.ai.mit.edu (Carl Heinzl) writes:
>>>3) what happens if one uses a standard valve in a LP steel tank, but
>>>routinely (illegally) pump it up to 3000 PSI, same as an AL tank?
>
>>You will wear out the burst disk, and also the posibility of blowing
>
>#1) - WHAT burst disk... If you don't know what I mean here - go
>ask on techdiver.
A burst disk is a copper waffer in the burst disk so that it will rupture
when the tank is over preasurized before the tank could have damage to it
from a crack. It will expand evertime you fill and especially when it is
over filled. Most of them will rupture about 7-900 psi over rated fill of
what the tank is if there was a proper disk put on the valve. Some people
do not know what a burst disk is and you do not have to go to techdiver to
find out what it is.
>
>>yourself and the place that you are filling the tank to kingdom come!!
>
>#2) - You have GOT to be kidding yourself. LP steels are ROUTINELY
>pumped up to anywhere from 3000-4000. These things aren't going to
>fracture at any rated pressure that any compressor at any dive store can
>put out, that's for sure. There are plenty of stores that you take
>in your tanks and they simply say "how much" or "how high".
Tanks are not routinely filled to the kind of pressures except in some
Florida areas. Carl is just trying to impresse everyone with his macho
image as a new cave diver.
>
>>DON"T do it. You can safely go approx 10% higher on the woking pressure
>>of a tank. But all shops will usually fill only to the stamped working
>>pressure.
>
>Baloney... I suggest you go to the bank and withdraw a clue - you need
>one.
Carl you need the clue as you do not know what you are talking about. You
have not had your tanks long enought to have a hydro done on them since
you started cave diving this year. What you will find out is that when
you overfill them you are regularly expanding the tanks and they will not
pass hydro for the expansion portion of the test. I am sure with all of
your money that buying new tanks every five years is no problem but it
certainly does not increase you intelegence factor.
>
>-Carl-
>
>Q. How often do you hydro your tanks?
>A. Every time I fill'em.
What a stupid answer.
diver...@aol.com
>Did I get it wrong?
>
>We measure the tanks in litres. But the volume is the internal
>volume. You can also say that it holds 12 litres of air in sea level
>perssure. If you fill a 12 litres tank with 200 bars (~3000 psi), it
>holds twice as much air than if you fill it with 100 bars. It is
>still a 12 litres tank. This way, when you buy a tank, or when you
>talk about one, you know its size.
>Regards,
>Kuty
You are correct about the AL 80's in th US but I believe that it would be
the same with your tanks as to the amount of air in the tank. If your
tanks were not filled to the rated pressure then you would not have as
much air as the tank should hold. The Internal water volumn of a tank is
measured and with the rated fill presure you can detemin the amout of
total air capasity in a tank. In your example of a 12 liter tank would
that not be the same as cuft rating of a tank over here? I guess that I
am going to have to learn how to convert to metric which we should have
done years ago. Does the liter rating on a tank refer to internal water
volumn or to volumn of air in the tank when filled to capasity. If it
referes to air then you would not have 12 liters of air in the tank if it
was filled to 100 bar. The space would be filled but it would only be
half filled as to pressure and not to volumn of air. I will check with
some poeple over here and see what I can find out. It is a very
interesting question.
Jammer
In article <5a7s32$o...@news.NetVision.net.il>, ku...@nite.org.il (Kuty) wrote:
€>Did I get it wrong?
€>
No, you got it exactly right.
€>This way, when you buy a tank, or when you
€>talk about one, you know its size.
We know it's size.
When I was in Norway, no one could tell me how big the tank I was renting
was, nor if my regulator would work on it. It was great fun.
Three Norwegians and me, with a calculator, yelling at each other in
different languages.
-------
"huh?"
--Jammer, 1992
-------
Jim Barteck
Jason wrote:
> I think it's quite strange that aluminium tanks are still heavily used
> in the US, whereas in Britain they're now relatively rare. I can't
> think of anyone I know who uses aluminium tanks.
The primary reason for the lasting popularity of aluminum tanks is
price, price, price. An aluminum 80 can be purchased in the $100-$150
range depending on your source while steel tanks typically start at
around $250 and go up from there. Until this price difference is
eliminated, you'll probably never see aluminum tanks go away...
Kenneth A.Smith (in California)
Also, since they are so popular, recent vintage , used tanks can be had
for not more than $70 US. Cant beat the price as Jim said.
Ken
Jason Rogers
If my translations are correct, the standard american "80" is about
a 10.5 litre 207 bar cylinder.
A fair bit smaller than the standard australian cylinder, which is
an 11.5 litre, 240 bar cylinder.
Here we have an interesting mish mash, having only converted to metric
in 1975, most people haven't fully switched yet.
Here all cylinders are sold (and talked about) by their cuft rating when
filled to their intended working pressure. (Interestingly, this is
usually the next interger down from the real capacity, in contrast to
the americans who seem to round up to the nearest 10)
Personlly, I agree with the americans, in that I *can* use both systems,
but I find the cuft easier to plan with. That's becuase
1 cuft/atm/minute is about the most that you'll ever use on a dive, so
for instance if you have a "95" and decide to reserve 15 cuft, then you
have "80" of useable gas. On the surface that will last at least
80 minutes. (nice easy calculation!) at 10 metres it lasts 40 minutes
at 30 metres it lasts 20 minutes, at 70 metres it lasts 10 minutes.
So easy that you can even do it on a dive boat, during the breifing.
Compared with the metric system! (I'm a big fan of metric normally)
An 11.5 litre cylinder, filled to 24 Mpa. (Standard cylinder) gives
276000000 litrepascals. Divide by 101300 Pa (the number of pascals
in one atmosphere) gives about 2725 litres of free gas. Say you reserve
500 litres, (about 16 cuft) that leaves you with 2225 litres of free air.
You're pretty safe to say you'll use less than 28 litres of air on the
surface (a fraction over 1 cuft), so you can divide the 2225 litres
by 28 to find out how long it will last on the surface.
79.46etc minutes
Hey! that's the same number of minutes we got by taking 15 away from
95! From there on the calculations are the same. (Ok, I used metres
for depth in both, but I think most people who use the imperial system
remember that atms are at 0, 33, 66, 99, 132 etc feet, down to the depth
they dive)
(Many europeans will not be familiar with "pascals". They are infact
the standard unit for pressure in the metric system. "Bar" is a
bastardisation that was introduced becasue pascals are such a pain.
A "pascal" is infact one Newton per Square Metre. A Newton is the force
that is required to accelerate one kilogram at one metre per second
per second. Since the normal "one gravity" is 9.8 metres/second/second.
One kilogram, sitting on the ground exerts a force (due to gravity)
of 9.8 Newtons. So the mass that will exert 1 Newton (under one gravity)
is 1/9.8th of a kilogram or about 102 grams.
102 grams is "small". One square metre is "large" (compared to say
one square inch, which is about 1/1500th the size).
When you divide "small" by "large" you get a bloody pain in the arse.)
Cheers Jason =:)
Jason Rogers
Here's a question for Hugh.
Here the Australian Standard 1777 Seemless Aluminium Pressure Vessels,
requires that working pressures be stated at 15 degrees Celsius, and
that cylinders be capable of withstanding temperatures up to 65 degrees
celsius.
Have I been correct in assuming that I'm *not* overstressing the
cylinder if I fill it to the pressure that it would have at 65
degrees, if it had been filled correctly at 15 degrees, as long
as I don't allow the temperature of the cylinder to rise above the
filling temperature (like fill at the dive shop on the wharf, carry
it out to the boat, ride 1/2 an hour out, and jump in)
The Australian standard for hoop overwrapped aluminium pressure vessels
has something similar, and the cylinders have printed on them both
the working pressure at 15 degrees, and the maximum pressure at 65
degrees. (for the ones I work with this is 39.5 Mpa at 65 C! or
5725 psi!)
Cheers Jason =:)
Carl Heinzl
> In the U.S., tanks up to 3300 psi come from the distributor with K
>valves (compact aluminum tanks are rated to 3300, standard aluminums
>typically to 3000). 3500 psi tanks come with DIN valves.
I'm not sure exactly what you mean by "compact aluminum tanks", however,
all the aluminum ponies that I've seen are rated to 3000. In addition,
I used to see 3300 PSI Aluminum 100's in dive stores, however, I'm not
sure if they're still around or not. These are not "guesses",this
is actual observed fact.
Can you reconcile these different observations?
-Carl-
Carl Heinzl
Jason,
>I think it's quite strange that aluminium tanks are still heavily used
>in the US, whereas in Britain they're now relatively rare. I can't
>think of anyone I know who uses aluminium tanks.
Don't people use aluminum bottles for stages? they're perfect for
that.
-Carl-
Roy Nurmi
diver...@aol.com wrote:
>
> I checked with one of our distibutors and the US cuft and you Litre rating
> are the same principal. This is the amount of air that the tank will hold
> when it is filled to its maxium rated pressure.
Again, no it is not. A 10 l tank filled to 200 bar holds approximately
2000 l gas. If it is filled to 300 bar, it holds approximately 3000 l
gas.
These figures would be comparable with your 80 cuft (which equals 2265
l).
The mentioned 12 l is simply the inner volume of a tank saying nothing
of its capacity.
Feel free to quote above to your distributor ;-)
This seems to be explained n times in this thread, this is just my
two pennies worth added to the discussion.
--
! Roy Nurmi (Roy....@icl.fi)
Divers do IT deeper! ! Vuolukiventie 4 A 9
- Kongfutse - ! 00710 Helsinki, FINLAND
! tel. 09-351 5150
Kuty
diver...@aol.com wrote:
>I checked with one of our distibutors and the US cuft and you Litre rating
>are the same principal. This is the amount of air that the tank will hold
>when it is filled to its maxium rated pressure.
Your distributor in the US doesn't know s**t.
The 12 litres are the amount of water the tank can hold (not gas).
When we talk about a 12 litres tank (or a 10 or 15) we immediately
know its size. When you talk about an 80 cuft tank, you have to know
its working pressure to know its physical size.
> A 12 liter tank is about the same as our 100cuft. I hope this helps.
>Once again we are not that different if at all.
1. according to my calculations (after I understood your system) , a
standard 12 litres tank (the standard filling here is 200 bars = 3000
psi) is like your 3000 psi (200 bar) ~85 cuft tank (not 100 cuft).
(see calculations as a footnote).
2. It is very different becuase we refer to a tank according to its
internal water volume capacity WHICH DOESN'T CHANGE and you refer to
it as its internal air capacity IN A CERTAIN PRESSURE WHICH MIGHT
CHANGE.
With Regards,
Kuty
85 cuft tank at 200 bars (3000 psi), holds 0.425 cuft of water (or air
at sea level pressure = 1 bar).
1 ft = 30.48 centimeter
1 cuft (1 ft ** 3) = 28,316.85 cubic centimeter (30.48 ** 3)
1 litre = 1,000 cubic centimeter
0.425 * 28.31685 (litre) = 12.03466 litre
Kuty
jam...@oz.net (Jammer) wrote:
>€>This way, when you buy a tank, or when you
>€>talk about one, you know its size.
>We know it's size.
Not exactly. Not according to the cuft number.
When you enter a standard diving equipment store here (we don't have
diving shops, we have clubs, and you buy the equipment in a diving
equipment store which might belong to a club and might not), there are
three common tanks - let's call them small (10 litres) medium (12
litres) and large (15 litres).
If I tell someone here that I dive with a 15 litres tank, he knows
that this is the large one.
If you tell someone that you dive with a 100 cuft he doesn't know if
you dive with the small one (let's say a Posseidon that holds 300 bars
= 4000 psi working pressure) or the large one (let's say a Cressi Sub
that holds 200 bars = 3000 psi). BTW the sizes, pressures and brand
names are examples from real life.
>When I was in Norway, no one could tell me how big the tank I was renting
>was, nor if my regulator would work on it. It was great fun.
I am sure that the internal volume and the working pressure of the
tank were engraved on it. I am also sure that you had great fun.
About the regulator, I was hesitating to bring my reg to the
Caribbeans. It turned out that I could use it with no problems. I am
quite sure that your reg did fit in Norway. Right?
>Three Norwegians and me, with a calculator, yelling at each other in
>different languages.
I sure would have loved to see this sight.
Regards,
Kuty
Kuty
gas...@sydney.DIALix.oz.au (Jason Rogers) wrote:
>If my translations are correct, the standard american "80" is about
>a 10.5 litre 207 bar cylinder.
>A fair bit smaller than the standard australian cylinder, which is
>an 11.5 litre, 240 bar cylinder.
Hey, I suspect that you refer to what we call a 12 litres (actually it
is 11.5) tank but our working pressure is 200 bars. Are you Ausies
pushing the limits or are they manufactured differently? What is the
working pressure that is engraved on the tank?
>Personlly, I agree with the americans, in that I *can* use both systems,
>but I find the cuft easier to plan with. That's becuase
>1 cuft/atm/minute is about the most that you'll ever use on a dive, so
>for instance if you have a "95" and decide to reserve 15 cuft, then you
>have "80" of useable gas. On the surface that will last at least
>80 minutes. (nice easy calculation!) at 10 metres it lasts 40 minutes
>at 30 metres it lasts 20 minutes, at 70 metres it lasts 10 minutes.
That's interesting. I agree that in terms of planning the dive time
it is easier. I didn't know that.
In terms of refering to a tank as a load you have to carry, store etc.
it is easier to use its volume. It tels you everything about its
size. (and you have to admit that calculating pressure and depth in
meters and bars - 1 bar sea level, 2 bars 10 meters 3 bars 20 meters
.. is more convenient.)
Regards,
Kuty
H Ned Huntzinger
Jason Rogers wrote:
>
> Here's a question for Hugh.
>
> Here the Australian Standard 1777 Seemless Aluminium Pressure Vessels,
> requires that working pressures be stated at 15 degrees Celsius, and
> that cylinders be capable of withstanding temperatures up to 65 degrees
> celsius.
I'm not familiar with this Standard, so I'm not really qualified to answer
your question. But I can make some educated guesses and express opinions:
65C is ~150F, which I think was the temperature that I recall seeing listed
in some of my references as the temperature thresshold where metallurgical
properties (ie, strength) of (some/many/most/this?) grades of Aluminum Alloys
start to degrade significant enough that these reductions in performance
must be taken into account when designing the pressure vessel. Sorry, but
I don't have this reference in front of me and its been a few years, too.
> Have I been correct in assuming that I'm *not* overstressing the
> cylinder if I fill it to the pressure that it would have at 65
> degrees, if it had been filled correctly at 15 degrees, as long
> as I don't allow the temperature of the cylinder to rise above the
> filling temperature (like fill at the dive shop on the wharf, carry
> it out to the boat, ride 1/2 an hour out, and jump in)
My opinion is that its more important to keep the tank cooler than 65C
than to worry about a few hundred PSI variation at 15C, even if said
variation is above the rated fill pressure...I'm not exactly sure if
this is what you're asking, however.
-hh
Fred Tagge
H Ned Huntzinger wrote:
>
> Jason Rogers wrote:
> 65C is ~150F, which I think was the temperature that I recall seeing listed
> in some of my references as the temperature thresshold where metallurgical
> properties (ie, strength) of (some/many/most/this?) grades of Aluminum Alloys
> start to degrade significant enough that these reductions in performance
> must be taken into account when designing the pressure vessel. Sorry, but
> I don't have this reference in front of me and its been a few years, too.
That's 350F. Generallly the low end of the annealing range for most aluminum
alloys begins at about 300F and is complete by about 800F. Time at temperaturre
has a lot to do with just how soft it gets at a given temp. The response of a
particular alloy can vary widely within this range.
>
> > Have I been correct in assuming that I'm *not* overstressing the
> > cylinder if I fill it to the pressure that it would have at 65
> > degrees, if it had been filled correctly at 15 degrees, as long
> > as I don't allow the temperature of the cylinder to rise above the
> > filling temperature (like fill at the dive shop on the wharf, carry
> > it out to the boat, ride 1/2 an hour out, and jump in)
IMNSHO The pressure @ 65C is to be considered an *extreme* exposure to be
avoided if you wish a long predictable tank life. I know folks who commonly
overfill to as much a 90% of the hydro pressure of a cylinder. They'll also
destroy a tank after the first 5 year hydro period runs out and consider it a
"cost of doing business". They may get only 100 or so dives from a tank before it
is destroyed. At ~$250/tank that works out to about $2.50/dive added cost for the
benefit of the additional air & down time. This is a cost/benefit decision *THEY*
made based on *THEIR* understanding of the principals involved. They do not
expect the tank to survive the second 5 year period so they remove it from
service before the hazard of the overfill situation exceedes their personal
tolerance.
BTW those I'm referring to have their own compressor and do their own fills, so
safety of unaware shop personnel is not a factor.
FT
Kuty
c...@freeside.ai.mit.edu (Carl Heinzl) wrote:
>Jason,
>Don't people use aluminum bottles for stages? they're perfect for
>that.
What makes an aluminum tank better for stage than a steel one?
Regards,
Kuty
Jason Rogers
Bob said:
I checked with one of our distibutors and the US cuft and you Litre rating
are the same principal. This is the amount of air that the tank will hold
when it is filled to its maxium rated pressure.
Sorry, your distributor is wrong.
The US (and Ozzie) cuft rating is the amount of air that the cylinder
will hold, while the litre rating (8, 10, 12 etc) is the amount
of water the cylinder will hold.
To confuse matters, cylinders are sometimes rated by the number of
litres of air they will hold at maximum working pressure, but then
the numbers are more like 1800, 2200, 2500 etc.
Normally litre ratings are given with the working pressure, like
"4 litre 200 bar" (about 27 cuft) or "18 litre 232 bar" (about
150 cuft). That's so you can tell the difference between things like
"4 litre 200 bar" (27 cuft) and "4 litre 300 bar" (42 cuft)
Cheers Jason =:)
Ville Saari
In article <32C5D7...@videotron.ca> jfmezei <nospam....@videotron.ca> writes:
> Ville Saari wrote:
> > Wrong. Buoyancy change is the weight of the air taken off the tank and
> > 120 cubic feet of air weights exactly the same no matter how much you
> > compress it. 4kg or 9lbs. So the buoyancy changes are the same.
>
> Wrong ! 120 cubic feet is the room size. It says nothing about how many
> people (molecules of air) you put in it
Wrong! Your room has certain pressure and it's temperature is in certain
range, so 120 cubic feet ofair specifies the number of molecules in it
quite accurately: about 85000000000000000000000000.
> and says absolutely nothing about how much it will weigh. (or more
> precisely how much its mass will be).
The mass of an air molecule is about 0.000000000000000000000000048 kg.
Multiplying these numbers gives about 4.1 kg. What's the problem?
> Why are you assuming that the higher pressure tank has lower volume ?
We were talking about tanks of the same capacity and higher
pressure tank *has* smaller internal volume than lower pressure
tank of the same capacity. Otherwise it wouldn't be higher pressure
tank.
--
Ville Saari EMail: v...@iki.fi
Tallbergin puistotie 7 B 21 Phone: +358 9 682 2226
00200 Helsinki
FINLAND /dev/null: write failed, file system is full
Ville Saari
In article <32C5E5...@videotron.ca> jfmezei <nospam....@videotron.ca> writes:
> > So all that matters, is the weight of the contents of the tank and
> > a pound of air weighs exactly one pound no matter what kind of a
> > tank it's in.
>
> NOt perfectly correct. The weight of the water being displaced depends
> on the volume of your tank. And that pound/kilo or air in your tank will
> occupy a different volume depending on your tank size.
But that volume does not change when the air is consumed, so it
has no effect on the buoyancy _change_.
And a pound of air still weighs one pound in any tank in any pressure.
(or if we are *really* accurate, it weighs actually a little bit more
in higher pressure tank because you need energy to compress the air
and the mass of that energy also goes into the tank, but the difference
is so small it doesn't have any practical significance)
Nigel Pond
Another interesting point is that burst disks are not required under the
UK regulations. The rationale being that the standards for wall
thickness etc, and manufacturing tolerances are higher therefore no need
for the disk. That's all fine until you move from the UK to the US like
I did. Of course I could not use a US tank valve with a disk as the neck
thread is different (imperial vs metric). I was lucky enough to find a
valve manufacturer in the UK who had a spare UK metric thread valve with
burst disk. But what a pain in the a**.
Wilson Angerson
In article <5a9jgs$2bl$1...@sydney.DIALix.oz.au>, Jason Rogers wrote:..
>Personlly, I agree with the americans, in that I *can* use both systems,
>but I find the cuft easier to plan with. That's becuase
>1 cuft/atm/minute is about the most that you'll ever use on a dive, so
>for instance if you have a "95" and decide to reserve 15 cuft, then you
>have "80" of useable gas. On the surface that will last at least
>80 minutes. (nice easy calculation!) at 10 metres it lasts 40 minutes
>at 30 metres it lasts 20 minutes, at 70 metres it lasts 10 minutes.
>
>So easy that you can even do it on a dive boat, during the breifing.
You make a persuasive case for what Kuty called a fucked-up system (if
my memory serves me right). 1 cuft/min is hard to beat for simplicity
when it comes to mental arithmetic. This system is fine if you know your
tanks are filled to their rated pressure. But when I was in the US and
hired an "80" filled to 2600 psi, I needed more information to work out
how much air I really had. If it had been called a 12 litre tank I would
have known all I needed.
I'm not arguing with what works for you, and I guess we all have our
personal systems for this kind of planning. There are pros and cons
to both methods, and I think it's important to be able to work with
both. I do wonder about the people that don't seem to be able to work
with either ("Hey, where did all my air go!? SUUUUUUUCK!") :-)
>Compared with the metric system! (I'm a big fan of metric normally)
Strictly speaking, the issue of metric versus non-metric units is
separate from that of whether you specify a tank's capacity by its
internal volume or by the amount of air it will hold at some specified
pressure, though I agree that in practice they go together.
>
>An 11.5 litre cylinder, filled to 24 Mpa. (Standard cylinder) gives
>276000000 litrepascals.
equals 276000 Joules
equals 276000 Watt seconds
And here you see the true beauty, simplicity and utility of SI
(International System, loosely known as metric) units. You can easily
work out how long you can power your dive light by emptying your tank
through a turbine generator. Try doing that with yer cubic bloody feet
mate! :-)
>Divide by 101300 Pa (the number of pascals
>in one atmosphere) gives about 2725 litres of free gas. Say you reserve
>500 litres, (about 16 cuft) that leaves you with 2225 litres of free air.
>
>You're pretty safe to say you'll use less than 28 litres of air on the
>surface (a fraction over 1 cuft), so you can divide the 2225 litres
>by 28 to find out how long it will last on the surface.
>
>79.46etc minutes
Now what could be simpler than that? :-)
>
>Hey! that's the same number of minutes we got by taking 15 away from
>95! From there on the calculations are the same. (Ok, I used metres
>for depth in both, but I think most people who use the imperial system
>remember that atms are at 0, 33, 66, 99, 132 etc feet, down to the depth
>they dive)
10 beats 33, just as 1 beats 28.
>(Many europeans will not be familiar with "pascals".
I wish! Tyre pressures, blood gas pressures, the damn things are creeping
in everywhere. Did you mean Americans?
>[info about pascals deleted]
>When you divide "small" by "large" you get a bloody pain in the arse.)
A megapita?
>
>Cheers Jason =:)
Wilson
jfmezei
diver...@aol.com wrote:
> The size of a tank is measured by water volume per the maunfacture. This
> is stated in cubic inches and the approved DOT pressure of fill determins
> the air volume.
> A 80cuft tank rated to 3000PSI filled with 2500psi will contain more air
> than a 3500psi tank filled to 2500psi. This occures because the 3500psi
> tank will have a smaller water volume than the 300psi tank and therfore
> have less air in it.
Ok, I am very confused here.
I though that the "80 cu feet" measure was directely and solely related
to the actual tank size (inside). (or is it the volume including the
tank walls ?)
I would have therefore thorugh that if you fill two tanks of 80cu feet
to
2500psi, both tanks would have the exact same amount of air inside, no
matter what their max rating was.
Of course, if the "cu feet" measure refers to the outside volume, the a
difference in tank wall thickness and design will result in a difference
in the amount of air that is contained inside the tank at any pressure.
Are such differences significant or small enough to be dismissed ?
diver...@aol.com
In article <CGH.96De...@freeside.ai.mit.edu>,
c...@freeside.ai.mit.edu (Carl Heinzl) writes:
>I'm not sure exactly what you mean by "compact aluminum tanks", however,
>all the aluminum ponies that I've seen are rated to 3000. In addition,
>I used to see 3300 PSI Aluminum 100's in dive stores, however, I'm not
>sure if they're still around or not. These are not "guesses",this
>is actual observed fact.
>
>Can you reconcile these different observations?
>
>-Carl-
The 3300 PSI tanks are sometimes call Fat 80s because they are larger in
diamater than a standard 80. This is also true of the 100's which also
weigh more. All AL tanks come in different fill preasure rating as to
pony bottle. The current supply is rated from 2015 to 3000 psi from 6 to
40 cuft. As you really do not get to that many shops nor have that much
real knowledge of what is availabe you would not be expected to know what
is actually available. Observation is juast opne of many ways to ahve
knowledge. A good Equipment specialty course would also help.
diver...@aol.com
In article <5aaitv$2n$1...@sydney.DIALix.oz.au>, gas...@sydney.DIALix.oz.au
(Jason Rogers) writes:
>Sorry, your distributor is wrong.
>
>The US (and Ozzie) cuft rating is the amount of air that the cylinder
>will hold, while the litre rating (8, 10, 12 etc) is the amount
>of water the cylinder will hold.
Agreeded that the litre designates the volumn as defined by water. But I
believe that you have tanks that are filled to different pressures per the
tank and do you not have a 12 litre at 200 bar and a 12 litre at 300 bar
or some difference. Or are you saying that on a 300 bar tank they make
them smaller so the capasity of the in air volumn never exceeds a certain
amount or size. The fill pressures on the same size water volumn on a
tank would produce considerably more air amount in the 300 bar 12 litre
than a 200 bar 12 litre tank.
>
>To confuse matters, cylinders are sometimes rated by the number of
>litres of air they will hold at maximum working pressure, but then
>the numbers are more like 1800, 2200, 2500 etc.
>
>Normally litre ratings are given with the working pressure, like
>"4 litre 200 bar" (about 27 cuft) or "18 litre 232 bar" (about
>150 cuft). That's so you can tell the difference between things like
>"4 litre 200 bar" (27 cuft) and "4 litre 300 bar" (42 cuft)
This is exactly what I am saying and the only difference is we designate a
tank by air volumn and then either LP or HP. If you do not know your
tanks then it is confusing to many diver about what the size of the tank
is or its buoyancy factors are. If you did not state the BAR rating the
you would not know the possible size of a tank or what its air supply
would produce. Our AL and LP steel and HP steel tanks are made of
different material and therefore vary the size and weight of the tanks.
Are your 200 and 300 BAR rated tanks made of the same material. If not
than your example of the 4 litre tank would have a different size and
weight to them.
>
>Cheers Jason =:)
KUTY
Your distributor in the US doesn't know s**t.
That is just your opinion but they deal on a world wide basis and may just
have a little more knowledge than you think.
The 12 litres are the amount of water the tank can hold (not gas).
When we talk about a 12 litres tank (or a 10 or 15) we immediately
know its size. When you talk about an 80 cuft tank, you have to know
its working pressure to know its physical size.
Unless the material were the same as stated above the tanks should be of
different size and weight. You may have all the tanks the same size for
internal volumn but the amount of air in the tanks will differ
considerable.
> A 12 liter tank is about the same as our 100cuft. I hope this helps.
>Once again we are not that different if at all.
1. according to my calculations (after I understood your system) , a
standard 12 litres tank (the standard filling here is 200 bars = 3000
psi) is like your 3000 psi (200 bar) ~85 cuft tank (not 100 cuft).
(see calculations as a footnote).
Our Al 80 only has 78cuft of actual air. I am going to check and find out
the actual water volumn in the different tanks then your calculation can
be used to determine actual amounts. I will also give you the physical
dimensions for the tanks and would like to know the same about your tanks.
2. It is very different becuase we refer to a tank according to its
internal water volume capacity WHICH DOESN'T CHANGE and you refer to
it as its internal air capacity IN A CERTAIN PRESSURE WHICH MIGHT
CHANGE.
You tanks have the same principal of change in air capacity as does ours.
It does not matter if you are filling a tank measured by cuft or liters.
When you are determining your air consumption for a dive you have to know
the amount of air available and what you are going to use during the dive.
Knowing the amount of water it holds does not matter. What does matter
is how much air will you have and that is a factor of pressure the vessel
is being filled to and the volumn of space inside the vessel. That
principal is the same world wide. You certainly would not do a dive with
100 BAR of fill and expect to have the same air supply as if it was filled
to 200 or 300 BAR.
With Regards,
Kuty
85 cuft tank at 200 bars (3000 psi), holds 0.425 cuft of water (or air
at sea level pressure = 1 bar).
1 ft = 30.48 centimeter
1 cuft (1 ft ** 3) = 28,316.85 cubic centimeter (30.48 ** 3)
1 litre = 1,000 cubic centimeter
0.425 * 28.31685 (litre) = 12.03466 litre
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jfmezei
I took my old chemestry book and here is how it goes:
Avogadro stated:
Equal volumes of gasses, weighted in the same temperature and pressure
conditions will have the same number of molecules (but weight
differently).
one "mole" is the number of molecules contained in a VOLUME of 22,4
litres,
a TEMPERATURE of 0 degrees, and PRESSURE of 101 kPa.
A mole is 6,02* 10^23 molecules. (eg: a big number).
These messures are all based on TPN (Temperature, Pression Normales)
which is: 0 degrees and 101 Kpa). (1ATM)
Now: 1 millilitre is one cubic centimetre. (hence you see ml or cc as
abreviations for volume).
So, one could find a direct conversion between a litre and a cubic feet.
I assume that americans know how many cubic feet a US gallon occupies or
how many ounces a cubic inch takes.
If you state the capacity of a scuba tank in its VOLUME and PRESSURE,
you still do not know how much air you have inside the tank because you
have not specified TEMPERATURE. (A hot tank will hold less air than a
cold tank filled to the same pressure).
So, a statement of "120 cubic feet" is not enough.
In my PADI manual, the following is stated:
The tank volume is expressed in Kilograms or Litres of WATER
capacity.
(1 litre of water weighs 1kg).
Since water is basically not compressible, the tank rating, which is
based on volume occupied by water, CANNOT have anything to do with rated
pressure.
If the USA measure in cubic feet is a direct conversion of the worldwide
standard in litres, then it too, would be a measure of volume/space
which is available to put stuff in, and would refer to a liquid (water)
being put in.
If, on the other hand, the USA measure of cubic feet does not refer to
the volume of water which can be put into the tank, then this measure,
without any other parametres, is TOTALLY MEANINGLESS.
120 cufeet can contain lots of air, very little air, and the amount of
air would vary according to temperature and pressure. The weight of
such
tank when filled to capacity would also vary depending on the gas you
use.
So, please, in the interest of consistency, I would ask those who claim
that
a 120cu feet tank rated at 3000 PSI is not the same size as a 120cu feet
tank rated at 2000 PSI to take their books out and explain exactly what
this
"120 cu feet" really means in terms of diving, because by itself,
"120 cubic feet" measures a space/volume/size and is totally unrelated
to
pressure and temperature which are variables which affect the amount of
air (capacity) of a tank.
Since the metric standard of litres refers ONLY to volume (litres), and
since the USA measures refer to volume (cubic feet), please understand
that we are confused when americans insist on saying that 120cufeet is
also related to pressure.
22,4 litres of air, at sea pressure (101kPa, and 0 degrees celcius
contain
6,02* 10^23 molecules of air.
How many molecules of air are contained in a USA "cubic feet" tank
measure ?
jfmezei
Avogadro stated:
Therefore, a 10,000 PSI tank of 120cu feet, is the exact same size as
a 3000 PSI tank of 120cu feet and will contain the exact same amount of
air
if both are filled to 2000 psi.
A 10,000 PSI , 120cu feet tank will contain exactly the same amount of
water than a 3000 PSI 120 cu feet tank.
However, the "120 cu feet" (or xx litres) does define precisely the
volume of water displaced by the tank since it has nothing to do with
the outside volume of the tank. (eg: excludes tank walls). It defines
solely the water capacity of the tank.
You will note that the PADI book states that in Australia, tanks have
the
"WATER CAPACITY" measure stamped onto the tank to indicate its volume.
The USA cyclinders do not have to have such measure.
Now I am less confused !
Jason
> The primary reason for the lasting popularity of aluminum tanks is
>price, price, price. An aluminum 80 can be purchased in the $100-$150
>range depending on your source while steel tanks typically start at
>around $250 and go up from there. Until this price difference is
Well aluminium tanks aren't quite that cheap over here. The steel
prices seem about the same. I think the extra's worth it myself. The
232 bar aluminium tanks I've used weigh quite a bit more than the
steel ones and require you to have an extra 5lbs lead on your belt.
And let's face it, $100 doesn't buy you a great deal of diving kit,
does it?
Jason
diver...@aol.com
In article <32C89B...@wmvx.lvs.dupont.com>, Nigel Pond
<pon...@wmvx.lvs.dupont.com> writes:
Do people overfill tanks as some due in the US to extreme pressures?
Another reason is that we tend to have much hoter temperatures and a tank
lying out the the SUN can build up a lot of pressure. I have heard that
SUN is not a year round occurance in the UK : ). The burst disk will keep
the tank from expanding the walls of the tank and shorting the life of the
tank by ruperturing at about 7-900 psi over rated fill presure. When you
came over was your tank already DOT approved? I can not think of why it
would be but if it is not stamped for DOT on the tank then it can not be
used over in the US legally.
diver...@aol.com
In article <32C942...@videotron.ca>, jfmezei
<nospam....@videotron.ca> writes:
>Ok, I am very confused here.
>
>I though that the "80 cu feet" measure was directely and solely related
>to the actual tank size (inside). (or is it the volume including the
>tank walls ?)
The 80cuft relates to the amount of air that can be compressed into the
cylinder when it is filled to its rated pressure. therfore and AL 80
3000psi is 7.25" in diameter 26.0 " in length, weighs 31.7 lbs empty w/o
valve and +3.9 lbs buoyant empty and holds 77.4 cuft. A HP Steel 80
3500psi is 7.25 " in diameter, 19.7 " in length, weighs 27.0 lbs empty w/o
valve, -1.0lb buoyant empty and holds 80.6 cuft when filled. Buoyance is
based on seawater w/o valves. As you can see there is a large difference
between an AL80 at 3000psi and a HP steel 80 at 3500 psi. There is an
even bigger difference if intorduce a LP Steel 80 at 2260 or what ever
pressure it is rated at.
>
>I would have therefore thorugh that if you fill two tanks of 80cu feet
>to
>2500psi, both tanks would have the exact same amount of air inside, no
>matter what their max rating was.
absolutly not. The smaller the internal volumn by water measurement is
directly effect the amount of air that will be in the container when two
different psi rated containers are filled to the same pressure. I hope
this helps a little.
>
>Of course, if the "cu feet" measure refers to the outside volume, the a
>difference in tank wall thickness and design will result in a difference
>in the amount of air that is contained inside the tank at any pressure.
>Are such differences significant or small enough to be dismissed ?
CUft is related to internal volumn of a cylinder.
Jim Barteck
Carl Heinzl wrote:
> I'm not sure exactly what you mean by "compact aluminum tanks", however,
> all the aluminum ponies that I've seen are rated to 3000. In addition,
> I used to see 3300 PSI Aluminum 100's in dive stores, however, I'm not
> sure if they're still around or not. These are not "guesses",this
> is actual observed fact.
>
> Can you reconcile these different observations?
>
Sure...we're talking about the same exact things...Manufacturers call
those 3300 psi tanks "compact aluminum" tanks because they used to also
sell 3000psi 100 cf aluminums (which were of course much larger) as
well. I haven't seen the 3000 psi models on the distributor's lists for
a couple of years, but they may well be out there somewhere as well.
The 3300psi 100 cf aluminums are still around, but it's almost
impossible to find the 3300psi 80 cf models new from the factory any
more...
diver...@aol.com
In article <32C957...@videotron.ca>, jfmezei
<nospam....@videotron.ca> writes:
>
>If you state the capacity of a scuba tank in its VOLUME and PRESSURE,
>you still do not know how much air you have inside the tank because you
>have not specified TEMPERATURE. (A hot tank will hold less air than a
>cold tank filled to the same pressure).
Temperature does have an effect in the real world of filling a tank. A
hot fill when it cools to 70 F will loose about 5-700 psi in pressure.
This is a subatantail amount but all tanks when rated are done so at a
designated temperature. The converse hold true that when you lower the
temperature of the tank you will loose pressure such as diving in 33-50 F
water.
>
>
>So, a statement of "120 cubic feet" is not enough.
In the US the designation of cuft is when the cylinder is filled to the
stated pressure stamped on the tank it will hold that amount of air at a
set temperature. Therefore andy change of psi will either under state or
overstate the amount of air in a tank. THe same will hold true for your
tanks. If a tank is not filled to its rated psi then it will hold a
different amount of air. I am asking if you do not have a stated psi
rated pressure on your tanks? You must have some point to know when the
tank is filled to capasity. So the 120 or 80 or 100 cuft is enough. We
are use to looking at the fill pressure on a gauge to know if the tank is
completely filled. Do you not do the same to check a tank to know if it
is filled or not.
>
>In my PADI manual, the following is stated:
>
> The tank volume is expressed in Kilograms or Litres of WATER
>capacity.
> (1 litre of water weighs 1kg).
>
>Since water is basically not compressible, the tank rating, which is
>based on volume occupied by water, CANNOT have anything to do with rated
>pressure.
The Water volumn has nothing to do with the pressure rating on a tank. It
does have a direct relation to how much air can be pumped into the tank
based on the rated psi pressure of a tank within a certain space.
>
>If the USA measure in cubic feet is a direct conversion of the worldwide
>standard in litres, then it too, would be a measure of volume/space
>which is available to put stuff in, and would refer to a liquid (water)
>being put in.
Are you saying that liters of volumn only relate to water and air is not
measured in the same way. When you determin your air consumption needs
for a dive is it not based on the amount of air and not water volumn? How
do you measure the amount of air in a given space under pressure?
>
>If, on the other hand, the USA measure of cubic feet does not refer to
>the volume of water which can be put into the tank, then this measure,
>without any other parametres, is TOTALLY MEANINGLESS.
It is totaly relevant to each tank when filled to capasity per its DOT
approval. You can not determin the amout of air in your tanks unless you
know the volumn and the pressure rating of the fill.
>
> 120 cufeet can contain lots of air, very little air, and the
amount of
> air would vary according to temperature and pressure. The weight
of
>such
> tank when filled to capacity would also vary depending on the gas
you
>use.
>
>So, please, in the interest of consistency, I would ask those who claim
>that
>a 120cu feet tank rated at 3000 PSI is not the same size as a 120cu feet
>tank rated at 2000 PSI to take their books out and explain exactly what
>this
>"120 cu feet" really means in terms of diving, because by itself,
>"120 cubic feet" measures a space/volume/size and is totally unrelated
>to
>pressure and temperature which are variables which affect the amount of
>air (capacity) of a tank.
We rate the tanks this way so that if filled to its stated PSI then this
tank will have this amount of air in it every time. If it is filled to
more or less than we would have to compute the amount of actual air in the
tank. Our customers expect it to be a complete fill and not a short fill.
If you do not give a good fill divers will find somewhere else to get
their fills.
>
>Since the metric standard of litres refers ONLY to volume (litres), and
>since the USA measures refer to volume (cubic feet), please understand
>that we are confused when americans insist on saying that 120cufeet is
>also related to pressure.
The reverse is true because I do not understand why you are not concerned
with the amount of air you have in your tank and more concerened with the
volumn of the tank. I know somewhere is all of this that you must know
how much air you have in the tank . We are approaching the answere form
two different ways but somewhere we will end up with the same result. The
pressure that a tank is filled to is directly related to how much air you
have in a tank. Maybe the difference is that we have tanks with different
volumns of water that when filled to different pressures as allowed by DOT
end up with the same amount of air. Therefore an AL80 rated at 300psi is
much bigger than a HP steel 80 rated at 3500psi but they both have the
same amount of air in them. Does this help any at all.
>
>22,4 litres of air, at sea pressure (101kPa, and 0 degrees celcius
>contain
>6,02* 10^23 molecules of air.
>
>How many molecules of air are contained in a USA "cubic feet" tank
>measure ?
This will vary based on the PSI rating and the space that it is packed
into of various cylinders. The al80- will have a lesser density than a HP
steel 80.
It would help in this discussion if you would tell us where the amount of
air you have available is determined and how that is determined in a
regular dive.
Jason Rogers
Kuty wrote:
>gas...@sydney.DIALix.oz.au (Jason Rogers) wrote:
>
>>If my translations are correct, the standard american "80" is about
>>a 10.5 litre 207 bar cylinder.
>
>>A fair bit smaller than the standard australian cylinder, which is
>>an 11.5 litre, 240 bar cylinder.
>
>Hey, I suspect that you refer to what we call a 12 litres (actually it
>is 11.5) tank but our working pressure is 200 bars. Are you Ausies
>pushing the limits or are they manufactured differently? What is the
>working pressure that is engraved on the tank?
That's what is stamped on the tank. They actually have:
WC 11.5 Kg (Water capacity 11.5 Kilograms of water, which is
11.5 litres, becasue water is 1Kg/Litre)
TW 15.5 Kg (this is the mass of the cylinder without the valve,
it's used at hydro time, when the cylinder is checked
to make sure it hasn't lost more than a certian % of
material since manufacture)
WP 24.0 Mpa at 15 C (this is the fill pressure at 15 degrees)
TP XX.X Mpa (I can't remember the test pressure of a "95", and I
don't have one handy. About 36 Mpa)
AS 1777 (The Australian Standards Association standard for
Seamless Aulminium Pressure Vessels (unfired))
The Serial Number, something like XX1234, and the first test
hydro stamp (and of course, the subsequent annual hydro stamps)
They're *talking* about requireing the cylinder outlet thread size
and type be stamped on them too. Which should have been mandatory
right from the bloody start!
Finding somewhere to put the hydro stamp on a small cylinder is
getting hard!
Oh, they're aluminium of course. (hence the AS 1777)
Cheers Jason =:)
Jason Rogers
Hmm, No that's not quite what I was asking, but the reply was information
I didn't know I needed (but did need)
Thanks!
Cheers Jason =:)
H Ned Huntzinger
Fred Tagge wrote:
>
> H Ned Huntzinger wrote:
> >
> > 65C is ~150F, which I think was the temperature that I recall seeing listed
> > in some of my references as the temperature thresshold where metallurgical
> > properties (ie, strength) of (some/many/most/this?) grades of Aluminum Alloys
> > start to degrade significant enough that these reductions in performance
> > must be taken into account when designing the pressure vessel. Sorry, but
> > I don't have this reference in front of me and its been a few years, too.
>
> That's 350F. Generallly the low end of the annealing range for most aluminum
> alloys begins at about 300F and is complete by about 800F. Time at temperaturre
> has a lot to do with just how soft it gets at a given temp. The response of a
> particular alloy can vary widely within this range.
No, this reference was not an annealing temperature per se - it was a rated reduction
in properties when the operating environment exceeded that temperature.
FWIW, I *am* pretty sure that if it wasn't ~150F, it was still under ~200F, for it
struck me how very easy of a temperature it was to see in the field. I think this
may have been in Mark's Handbook or similar...I'll follow-up and relocate the reference.
> ...I know folks who commonly
> overfill to as much a 90% of the hydro pressure of a cylinder. They'll also
> destroy a tank after the first 5 year hydro period runs out and consider it a
> "cost of doing business". They may get only 100 or so dives from a tank before it
> is destroyed. At ~$250/tank that works out to about $2.50/dive added cost for the
> benefit of the additional air & down time. This is a cost/benefit decision *THEY*
> made based on *THEIR* understanding of the principals involved...
Tthat's a much better start than what others are doing. Do you know if they re-mark
the tanks in question and also keep a meticulous fill log on them as well? I suppose
it would be too much to ask if they're also doing frequent NDT's and/or measured
sidewall thicknesses before they even started...
-hh
H Ned Huntzinger
Kuty wrote:
> What makes an aluminum tank better for stage than a steel one?
They typically have "better" (ie, more desirable for the application)
bouyancy characteristics - AL80's are only slightly negative when
full and they float when they're empty.
-hh
Kuty
diver...@aol.com wrote:
>The 80cuft relates to the amount of air that can be compressed into the
>cylinder when it is filled to its rated pressure. therfore and AL 80
>3000psi is 7.25" in diameter 26.0 " in length, weighs 31.7 lbs empty w/o
>valve and +3.9 lbs buoyant empty and holds 77.4 cuft. A HP Steel 80
>3500psi is 7.25 " in diameter, 19.7 " in length, weighs 27.0 lbs empty w/o
>valve, -1.0lb buoyant empty and holds 80.6 cuft when filled. Buoyance is
>based on seawater w/o valves. As you can see there is a large difference
>between an AL80 at 3000psi and a HP steel 80 at 3500 psi. There is an
>even bigger difference if intorduce a LP Steel 80 at 2260 or what ever
>pressure it is rated at.
You see my dear friend Jean Francois, this is a very convenient way to
measure a tank.
As opposed to the complex European system of calling a tank 12 litres
and knowing that it is 20% bigger than the 10 litres and 20% smaller
than the 15 litres.
Regards,
Kuty
Egil Aabel Naesguthe
In article <32C94E...@videotron.ca>, nospam....@videotron.ca says...
>Therefore, a 10,000 PSI tank of 120cu feet, is the exact same size as
>a 3000 PSI tank of 120cu feet and will contain the exact same amount of
>air
>if both are filled to 2000 psi.
>
>A 10,000 PSI , 120cu feet tank will contain exactly the same amount of
>water than a 3000 PSI 120 cu feet tank.
>
>However, the "120 cu feet" (or xx litres) does define precisely the
>volume of water displaced by the tank since it has nothing to do with
>the outside volume of the tank. (eg: excludes tank walls). It defines
>solely the water capacity of the tank.
Let me just ask you one question: How many litres do 120 cu ft equal?
10? No! 12? No! 15? No again!
Just work it out and you will see that what you are saying makes no sense.
Egil
Richard Westlake
ja...@volnay.demon.co.uk (Jason) wrote:
>Our standard pressure is usually 232
>bar (3300 psi) and we use yoke fittings for that. Is it not possible
>to get 3300 psi tanks in the US with yoke fittings? And if not, why
>not?
You certainly can get 3300 psi tanks with yoke fittings in the US.
I have a pair of Luxfer 3300 psi aluminum tanks, 100 cubic foot
capacity ... that would be, what, 12-liter tanks to the CE folks?
And they came from the factory with 3300 psi yoke fittings.
Wish I'd gotten the high-pressure steel tanks, though.
(Last dive, this afternoon in Bainbridge quarry, Pennsylvania.
19 mins, 21 feet ... and me the only one in a wet suit.)
Nigel Pond
I beg to differ..the European system and the US system just approach
things in different ways. The Euro system gives the liquid volume of the
tank at 1ATM the US system assumes the rated pressure. Either way if you
understand that the *air capacity* of the tank is dependent on the
volume to which it is filled then all teh US and European systems do is
tell you how big a lump of metal you have to lug around on your back
and how much more or less it holds relative to another tank using the
assumptions valid for each tank.
This really is not rocket science.
ham...@evms.enet.dec.com
In article <32C942...@videotron.ca>,
jfmezei <nospam....@videotron.ca> writes:
>I though that the "80 cu feet" measure was directely and solely related
>to the actual tank size (inside). (or is it the volume including the
>tank walls ?)
Nope. The "80 cu feet" refers to an amount of air that occupies 80 cubic
feet at a pressure of one atmosphere. (On atmospehere presure is approximately
14.5 PSI.) It follows that the actual internal volume required to hold
80 cu feet depends on the pressure.
An 80 cu ft 3000 PSI tank has an internal volume a bit less than .4 cu ft.
80 * 14.5
--------- = .38666...
3000
An 80 cu ft 3500 PSI tank has a smaller internal volume.
80 * 14.5
--------- = .3314285...
3500
An 80 cu ft 2640 PCSI tank has a larger internal volume.
80 * 14.5
--------- = .4393939...
2640
--
Charlie Hammond -- Digital Equipment Corporation -- Nashua NH USA
(ham...@peek.enet.dec.com)
All opinions expressed are my own and do not necessarily reflect
my employer's position.
jfmezei
OK, let me restate my question:
In metric, PADI states that tank SIZE is measured in litres. 1 litre
is a very precise measurement of VOLUME which is totally independant
from temperature and pressure.
One litre of water tells you how huch water there is in there.
(OK, 1 litre at 4 degrees tells you EXACTLY, as there are minute
variations in the mass of water when temps vary from 4 degrees).
So, you know exactly how BIG a 11.5 litre tank is.
And you know that a 200 bar 11.5litre tank can contain twice as much
air as a 100 bar 11.5 litre tank even tough both tanks are the exact
same size. To know a tank's capacity, you need its size and max pressure
rating. This tells you how many molecules of air you can stuff in there
at a certain temperature.
Now, litre is a measure of volume which can also be expressed in
cubic centimetres and hence translated to cubic feet. Assuming very thin
tank walls, 1 one litre tank will displace one litre of water which
weighs 1kg (fresh water).
Here is where I get confused:
People have been saying that a 120cufeet 3000 psi tank is physically
smaller than a 120cufeet tank rated at 2000 psi.
Since cubic feet is a measure of volume, and since the volume of a metal
container does not change when you add or remove pressure to it, I do
not undertand what "120 cufeet" measure really means since it obviously
does not refer to the physical volume of the tank.
Therefore, I would ask someone to point out EXACTLY what a cubic feet
means in terms of tanks and provide any other "assumed" values such as
pressure and temperature which may be involved.
Nigel Pond
The cu ft capacity of a US tank is based on the assumption that it is
filled to its working pressure -- its short of shorthand for "X cu ft at
a pressure of Y psi"
--
The views expressed herein are the personal views of the writer and are
not to be considered endorsed in any way by E.I. du Pont de Nemours and
Company or any of its subsidiaries or affiliates.
Kuty
On 1 Jan 1997 13:36:00 +1100, gas...@sydney.DIALix.oz.au (Jason
Rogers) wrote:
>Kuty wrote:
>>Hey, I suspect that you refer to what we call a 12 litres (actually it
>>is 11.5) tank but our working pressure is 200 bars. Are you Ausies
>>pushing the limits or are they manufactured differently? What is the
>>working pressure that is engraved on the tank?
>
>That's what is stamped on the tank. They actually have:
>
>WC 11.5 Kg (Water capacity 11.5 Kilograms of water, which is
> 11.5 litres, becasue water is 1Kg/Litre)
>TW 15.5 Kg (this is the mass of the cylinder without the valve,
> it's used at hydro time, when the cylinder is checked
> to make sure it hasn't lost more than a certian % of
> material since manufacture)
>WP 24.0 Mpa at 15 C (this is the fill pressure at 15 degrees)
>TP XX.X Mpa (I can't remember the test pressure of a "95", and I
> don't have one handy. About 36 Mpa)
>AS 1777 (The Australian Standards Association standard for
> Seamless Aulminium Pressure Vessels (unfired))
>The Serial Number, something like XX1234, and the first test
>hydro stamp (and of course, the subsequent annual hydro stamps)
Well, Mine says:
FABER 89/012 (manufactured in 1989)
003 (serial # for that day)
ARIA 200/300 BAR (200 bars working pressure, 300 bars test)
15 LITRES (one can see in this thread what it means)
16.4 Kg (weight)
and the next hydro tests dates
Kenneth A.Smith (in California)
Hugh A. Huntzinger (CCL) wrote:
> Time for the NED Quiz...what do you call a 120ft^3 tank when it doesn't
> have any air left in it?
>
> The answer: EMPTY! :-)
>
> -hh
The other answer is ready for a VIP as most fill stations wont fill an
empty tank without one.
Ken
Hugh A. Huntzinger (CCL)
> To know a tank's capacity, you need its size and max pressure rating.
In the USA's "cufeet" system, the math has already been done for you.
The tanks are described by their (filled) capacity...ie "cufeet".
Now if you were curious as to the actual physical SIZE of the tank,
you would take the rated capacity ("cufeet") and divide by the max
pressure rating to figure this out.
Think of it this way: your 200bar 11.5 liter tank has a capacity
of (200)*(11.5) = 2300 liters, right?
Well, any tank called a 120ft^3 tank contains that much air after
it has been filled to its max pressure rating...ie, its its capacity.
In metric terms, its also (120ft^3)*(28.3 liters/ft^3) = ~3400 liters.
To figure out the SIZE of that 120ft^3 tank...
If it was a 200 bar tank (ie, 3000psi), then its 3400/200 = 17 liters big.
On the other hand, a 150 bar tank (2250psi) is 3400/150 = 22.66 liters,
which is a physically larger tank and the source of the statement that
was made that you questioned.
Jason Rogers
>Therefore, I would ask someone to point out EXACTLY what a cubic feet
>means in terms of tanks and provide any other "assumed" values such as
>pressure and temperature which may be involved.
>
dimention.
120 cuft (the subject of this thread) would be a cube about
5.313 ft on a side (a big box, that a quite short person could stand up
inside). That's the size of the air, before you stuff it into the
tank, (or after you take it out!)
If you have a low pressure tank that takes that much air, you'd
expect it to be large (it's a lot of air). It is ;)
If you had a high pressure tank, that held the same amoount of
air, you'd expect it to be smaller (because the air is stuffed in
tighter), and it is, indeed smaller.
Like having an 8 litre 300 bar cylinder, and a 12 litre 200 bar
cylinder. They hold the same amount, (2400 litres or about 85 cuft)
but the 8 litre cylinder is smaller, and you can take some lead
off your belt. (because you're displacing less water)
So "120 cuft" refers only to how much air can be stuffed into the
cylinder at the rated pressure of the cylinder. If you want to
know if it is a big or small cylinder, you have to ask what it
is made of (steel cylinders are smaller than aluminium) and what
it's rated fill pressure is. (and it would help to know if it has
been "derated" because a cylinder made for a higher pressure will
have thicker walls, making it bigger (outside) than you might expect
judging by it's "derated" pressure)
Does this clear it up?
Cheers Jason =:)
forsp...@aol.com
In article <32CBCE...@videotron.ca>, jfmezei
<nospam....@videotron.ca> writes:
>One litre of water tells you how huch water there is in there.
>(OK, 1 litre at 4 degrees tells you EXACTLY, as there are minute
>variations in the mass of water when temps vary from 4 degrees).
Remember, water is essentially noncompressible. Air is easily compressed.
Measuring water capicty by inside tank volume in liters, quarts etc is
fine. For gas, you must consider its pressure inside the container, not
just the "size" of the container.
>So, you know exactly how BIG a 11.5 litre tank is.
>And you know that a 200 bar 11.5litre tank can contain twice as much
>air as a 100 bar 11.5 litre tank even tough both tanks are the exact
>same size. To know a tank's capacity, you need its size and max pressure
>rating. This tells you how many molecules of air you can stuff in there
>at a certain temperature.
>
>Now, litre is a measure of volume which can also be expressed in
>cubic centimetres and hence translated to cubic feet. Assuming very thin
>tank walls, 1 one litre tank will displace one litre of water which
>weighs 1kg (fresh water).
>Here is where I get confused:
>
>People have been saying that a 120cufeet 3000 psi tank is physically
>smaller than a 120cufeet tank rated at 2000 psi.
>
>Since cubic feet is a measure of volume, and since the volume of a metal
>container does not change when you add or remove pressure to it, I do
>not undertand what "120 cufeet" measure really means since it obviously
>does not refer to the physical volume of the tank.
>Therefore, I would ask someone to point out EXACTLY what a cubic feet
>means in terms of tanks and provide any other "assumed" values such as
>pressure and temperature which may be involved.
A conversion to cu.ft. as you describe is not the "cu.ft." concept being
referred to when we speak of, for example , an "80 cu.ft. tank ". That "80
cu ft" tank is not a reference to the interior volume of the tank in
absolute terms (as liters of water would be)but rather refers to a
container which at rated pressure (eg, 3000 psi) will contain the
equivilent of 80cu ft of gas at STP (standard tempeture and pressure). STP
is 1 atmosphere sea level (I forget the tempeture in degrees celcius). 80
cu. ft. is roughly equivlent to the amount of air in a typical closet or
phone booth (volume 80 cu ft at 1 atmosphere of pressure). At higher
pressure, that same "80 cu.ft." could be in a smaller container such as an
"aluminum 80". Lower pressure, larger container needed fot the same "80
cu. ft" . At "rated pressure" of tank, you get what would be "x" cu. ft.
of gas if the gas were at STP instead of being compressed inside the tank.
In that sense, it is a "volume" measure, but a "volume " of compressed
gas, not a measured volume of the inside of the tank.
Hope that helps
>
Steve Burke
for...@aol.com
jfmezei
ham...@evms.enet.dec.com wrote:
> Nope. The "80 cu feet" refers to an amount of air that occupies 80 cubic
> feet at a pressure of one atmosphere. (On atmospehere presure is approximately
> 14.5 PSI.) It follows that the actual internal volume required to hold
> 80 cu feet depends on the pressure.
At what temperature ?
"80 cubic feet" still doesn't tell me how much air it is unless you tell
me at what temperature is was at.
I would have hoped that they would have found a different name for the
units
used in the USA as this is definitely very misleading to just say "80 cu
feet".
If people regularly used "80 cubic feet of clean air at 1 ATM and at
temperature X", then I would not have been confused. If special units
had been used, I would not have been confused.
Jim Barteck
jfmezei wrote:
> At what temperature ?
>
I believe 70 degrees Fahrenheit is the standard used to determine
proper filling pressure....for instance, 3000 psi at 70 degrees
Fahrenheit....tanks in the U.S. are rated by the amount of air they will
hold at the rated pressure at (I believe) 70 degrees Fahrenheit...
(Kind of makes you think about that 2700 psi fill you got last time you
were in the Caribbean when the air temperature was a lot closer to 90
degrees doesn't it?)
Jason Rogers
>If people regularly used "80 cubic feet of clean air at 1 ATM and at
>temperature X", then I would not have been confused. If special units
>had been used, I would not have been confused.
>
gather that the US "80" refers to 77.4 cvft at STP.
Most people don't bother with the temperature, as the variations
in the actual fill from factors like Van der Waal's forces and
inacuracies in the filling gauge would swamp most normal temperature
effects (in the sort of rough room temperature world, 10-35 C)
Cheers Jason =:)
AS 1777 defines it as 15 degrees Celsius, which I think I posted
before. Oh, and "clean air" what do yo mean by that? I use
Ultra High purity air sometimes at work. It's Oxygen in Nitrogen,
better than 5 nines (99.999% N2 or O2). I also use air filtered to
AS 2299, which is over 1% impurities (such as argon), this is air
for underwater use. I also use air to AS 1726, which is less pure
even than 2299 air. It's for use in surface breathing equipment.
Michael J. Kravit, AIA
Holy Shit!
Carl, now I remember why I only download recscuba when I have a fever and I
am delerious.
What a stroke!
Mike
----------------------------------------------------------------------------
------------------------------------------------------------------
Carl Heinzl <c...@martigny.ai.mit.edu> wrote in article
<CGH.96De...@martigny.ai.mit.edu>...
>
> >>3) what happens if one uses a standard valve in a LP steel tank, but
> >>routinely (illegally) pump it up to 3000 PSI, same as an AL tank?
>
> >You will wear out the burst disk, and also the posibility of blowing
>
> #1) - WHAT burst disk... If you don't know what I mean here - go
> ask on techdiver.
>
> >yourself and the place that you are filling the tank to kingdom come!!
>
> #2) - You have GOT to be kidding yourself. LP steels are ROUTINELY
> pumped up to anywhere from 3000-4000. These things aren't going to
> fracture at any rated pressure that any compressor at any dive store can
> put out, that's for sure. There are plenty of stores that you take
> in your tanks and they simply say "how much" or "how high".
>
> >DON"T do it. You can safely go approx 10% higher on the woking pressure
> >of a tank. But all shops will usually fill only to the stamped working
> >pressure.
>
> Baloney... I suggest you go to the bank and withdraw a clue - you need
> one.
>
> -Carl-
>
> Q. How often do you hydro your tanks?
> A. Every time I fill'em.
>
Fred Egge
jfmezei wrote:
>
> ham...@evms.enet.dec.com wrote:
> > Nope. The "80 cu feet" refers to an amount of air that occupies 80 cubic
> > feet at a pressure of one atmosphere. (On atmospehere presure is approximately
> > 14.5 PSI.) It follows that the actual internal volume required to hold
> > 80 cu feet depends on the pressure.
>
> At what temperature ?
>
> "80 cubic feet" still doesn't tell me how much air it is unless you tell
> me at what temperature is was at.
>
> I would have hoped that they would have found a different name for the
> units
> used in the USA as this is definitely very misleading to just say "80 cu
> feet".
>
> temperature X", then I would not have been confused. If special units
> had been used, I would not have been confused.
-------
You guys have me really confused, These are both contrary to what I was
tought.
First, a 80 cu ft cylinder rated at 3000psi would have 80 cu ft of air
squished into it when @ 3000psi, and .394 cu ft @ 0psi(gauge)or
14.7psia.
What I have learned about temperature is that according to Charles law
(Jacques Charles)is that the amount of either volume and pressure is
directly porportional to the change in absolute tremerature. This would
mean that when a tank filled to 3000psi at approx. 85 degrees F (in the
shop) is brought to a ice dive at 33 degrees F it would lose both volume
and psi (it ends up about 200psi) proportionaly. Therefore if I filled
it back up to 3000psi in the ice water I would again have 80 cu ft.
Freezing in Michigan (but still diving)
Freddie
jfmezei
Fred Egge wrote:
> What I have learned about temperature is that according to Charles law
> (Jacques Charles)is that the amount of either volume and pressure is
> directly porportional to the change in absolute tremerature.
Well, there is a direct corrolation. I am not sure if "directly
proportional" is technically correct though.
> This would
> mean that when a tank filled to 3000psi at approx. 85 degrees F (in the
> shop) is brought to a ice dive at 33 degrees F it would lose both volume
> and psi (it ends up about 200psi) proportionaly.
Sorry, except for the minimal contraction of the metal itself because of
lower temperature, your tank's volume never changes, whether empty or
filled to 3000 psi.
You tank filled at 3000psi at 85F will have its pressure drop when
cooled.
It will still have the exact same amount of air inside.
But a tank filled to 3000psi at 32 degrees F will have much more air in
it than the same tank filled to 3000 psi at 85F.
This is why the temperature is a critical component of the USA "cufeet"
measure of tank capacity since "cufeet" does not measure volume but
rather
air capacity, and air capacity in a fixed true volume (your tank) varies
significantly with temperature).
JD TURNER
In responce to Fred Egge (aro...@iserv.net) who did lots of copying:-
No, If you re-read the previous posts the 80 cubic feet of air that you
are putting in you tank are 80 cubic feet of air from the atmosphere
surrounding the compressor. So, obviously this air has to be at a pressure
of 1 Atmosphere, and be of whatever temp you ambient air is on that day.
So, if you use the general gas law instead of charles law
GGL P1V1 = P2V2
---- ----
T1 T2
(hope it look O.K. on your screen)
You can use whatever units you like, as long as you use same on both sides
of the equation.
Back to where I was, using the ggl your 80 cubic foot at ambient press and
temp. will equal you right hand side of the equation with cylinder press
and temp. not forgetting of course the change in temp with compression.
Try it, it does work, the numbers dont quite work out because of the
inneficiency of the compressor and the fact that it is not an ideal gas.
But it does work out close enough to prove the point.
All that has confused you in the first part of the post is that you havent
realised that the 80cuf is 80 cuf of surrounding air at ambient T and P
In the second part of your post you are wrong in that lowering the temp of
the cylinder and then putting more air in you are bringing it back up to
the 80 cuf. If after filling in the ice water you let the tank and air warm
up the pressure would rise well in excess of the 3000psi (232 ATM), and if
you let the air expand back to atmospheric pressure, you would have a lot
more than 80 cuf. (think about it as putting in 80 from the surrounding air,
cooling it, and then putting in an extra 20 say, obvious now that you have
more than 80 cuf of air at ATMOSPHERIC pressure?)
or, think of it using the ggl, only this time put the lower put all the
variables except the atmospheric volume in, with the atmos temp and press
as before, again the cylinder (compressed volume) volume and pressure you
want (3000 psi) and the lower ice water temp. this proves the volume that
you would get in is more than 80 cuf.
Pelucid?
is to most peolpe probably.
: jfmezei wrote:
: >
: > ham...@evms.enet.dec.com wrote:
: > > Nope. The "80 cu feet" refers to an amount of air that occupies 80 cubic
: > > feet at a pressure of one atmosphere. (On atmospehere presure is approximately
: > > 14.5 PSI.) It follows that the actual internal volume required to hold
: > > 80 cu feet depends on the pressure.
: >
: > At what temperature ?
: >
: > "80 cubic feet" still doesn't tell me how much air it is unless you tell
: > me at what temperature is was at.
: >
: > I would have hoped that they would have found a different name for the
: > units
: > used in the USA as this is definitely very misleading to just say "80 cu
: > feet".
: >
: > If people regularly used "80 cubic feet of clean air at 1 ATM and at
: > temperature X", then I would not have been confused. If special units
: > had been used, I would not have been confused.
:
: -------
: You guys have me really confused, These are both contrary to what I was
: tought.
:
: First, a 80 cu ft cylinder rated at 3000psi would have 80 cu ft of air
: squished into it when @ 3000psi, and .394 cu ft @ 0psi(gauge)or
: 14.7psia.
:
: What I have learned about temperature is that according to Charles law
: (Jacques Charles)is that the amount of either volume and pressure is
: directly porportional to the change in absolute tremerature. This would
: mean that when a tank filled to 3000psi at approx. 85 degrees F (in the
: shop) is brought to a ice dive at 33 degrees F it would lose both volume
: and psi (it ends up about 200psi) proportionaly. Therefore if I filled
Fred Egge
Fred Egge Wrote:
I understand where I was confused in the first part about volume (I read
it to fast and thought you said that a 80 cu ft cylinder has 80 cu ft of
air in it when it is at 14.7 psi that is why I looked up the volume of a
3000psi 80 cu ft cylinder (.394cu ft)). This was MY misunderstanding
what YOU wrote, Sorry if I had offended you and thanks for the
explaination.
Egg on face (no pun intended)
Fred
Carl Heinzl
>>#1) - WHAT burst disk... If you don't know what I mean here - go
>>ask on techdiver.
>A burst disk is a copper waffer in the burst disk so that it will rupture
>when the tank is over preasurized before the tank could have damage to it
>from a crack. It will expand evertime you fill and especially when it is
>over filled. Most of them will rupture about 7-900 psi over rated fill of
>what the tank is if there was a proper disk put on the valve. Some people
>do not know what a burst disk is and you do not have to go to techdiver to
>find out what it is.
No shit sherlock. If you can't understand *sarcasm* then you really DO
need a clue, but that's pretty obvious anyway.
>>>yourself and the place that you are filling the tank to kingdom come!!
>>
>>#2) - You have GOT to be kidding yourself. LP steels are ROUTINELY
>>pumped up to anywhere from 3000-4000. These things aren't going to
>>fracture at any rated pressure that any compressor at any dive store can
>>put out, that's for sure. There are plenty of stores that you take
>>in your tanks and they simply say "how much" or "how high".
>Tanks are not routinely filled to the kind of pressures except in some
>Florida areas. Carl is just trying to impresse everyone with his macho
>image as a new cave diver.
I'm simply making a statement of *fact*.
>>>DON"T do it. You can safely go approx 10% higher on the woking pressure
>>>of a tank. But all shops will usually fill only to the stamped working
>>>pressure.
>>
>>Baloney... I suggest you go to the bank and withdraw a clue - you need
>>one.
>Carl you need the clue as you do not know what you are talking about. You
>have not had your tanks long enought to have a hydro done on them since
>you started cave diving this year. What you will find out is that when
>you overfill them you are regularly expanding the tanks and they will not
>pass hydro for the expansion portion of the test. I am sure with all of
>your money that buying new tanks every five years is no problem but it
>certainly does not increase you intelegence factor.
Perhaps you can tell us of *any* Pressed Steel 95s or 104s that have
*ever* failed hydro? Come on, impress us with your *personal
experience* which is just so great.
If you don't know what the hell these tanks are made of and the
pressures that they can take then no, you shouldn't be overfilling them,
but these tanks *easily* overfill and will pass hydro.
-Carl-
>>Q. How often do you hydro your tanks?
>>A. Every time I fill'em.
>What a stupid answer.
And that's certainly a witty retort, touche.
-Carl-