Connect two lpg tanks together
alex
correctly. One of them 48L toroidal placed below the vehicle, and another
one cylindrical 60L placed in a boot. My concern is usage of non-return
valves. On some treads I've read that it necessary to place non-return valve
on on one of the fuel lines to reducer, leaving one of the lines whithout
one for returning gas back to one of the tanks in case if gas expands in
fuel line (even if the system is switched off thats should direct some gas
back into the tank). That statement makes thing for me a bit unclear,- if
solenoid on multivalve is closed how the gas can get back into the tank? And
whats the point installing them non-return valves? As I understand the
pressure in connected pipe lines with "T" piece will keep 9 bar all the time
in the hole fuel line to reducer when both solenoids will be opened. If one
tank empties faster the other one will keep up the pressure in fuel line
anyway or thransfer some gas into the tank which is empty on low demand, so
whats wrong with this?
thanks
athol
I'm not familiar with the rules in UK, but the following is how it works in
AU...
The service valves on the LPG tanks are not check valves, and don't seal in
the reverse direction. If the pressure in the service line from the tank
to the convertor (vapouriser) is higher, for example due to heat from the
engine, exhaust, etc., some of the fuel can go back into the tank to relieve
the pressure in the hose.
If you have two (or more) tanks connected to the one service line, it's
theoretically possible to get liquid coming out of one tank into the service
line, then returning into the other tank as described above. This can be
influenced by suich things as the temperature that the tanks are at. If the
vehicle is drawing fuel from one tank and not the other (normal way of wiring
is to have a switch to select which tank's solenoid to turn on), this could
result in one tank filling beyond 80%, making it possible for liquid to come
out of the pressure relief valve in that tank (VERY dangerous).
The solution is to use a "hydrostatic relief and twin check valve" assembly.
The only brand I've ever seen is an USA company called "Sherwood", and hence
these valves are referred to as a "Sherwoood valve". These have 2 inputs
and one output, with check valves on both inputs and a relief valve on the
output. While this relief valve would discharge liquid, it's designed to be
able to do this. With a Sherwood valve in the service line, the excess
pressure will discharge through the relief and never return to either tank.
Given that the service line virtually never has enough pressure to return
fuel to the tank, this valve will probably never discharge any fuel.
--
Athol
<http://cust.idl.com.au/athol> Linux Registered User # 254000
The state of infrastructure in New South Wales is a disgrace.
I'm a Libran Engineer. I don't argue, I discuss.
Austin Shackles
thusly:
>alex <al...@yoursitenospam.com> wrote:
>> Could anyone here describe in details how to connect two lpg tanks together
>> correctly. One of them 48L toroidal placed below the vehicle, and another
>> one cylindrical 60L placed in a boot. My concern is usage of non-return
>> valves.
>I'm not familiar with the rules in UK, but the following is how it works in
>AU...
>
>If you have two (or more) tanks connected to the one service line, it's
>theoretically possible to get liquid coming out of one tank into the service
>line, then returning into the other tank as described above. This can be
>influenced by suich things as the temperature that the tanks are at. If the
>vehicle is drawing fuel from one tank and not the other (normal way of wiring
>is to have a switch to select which tank's solenoid to turn on), this could
>result in one tank filling beyond 80%, making it possible for liquid to come
>out of the pressure relief valve in that tank (VERY dangerous).
Given that both tanks have their own fill valves (with 80% shut-off) and
PRV, the basic requirement is non-return valve in both the tank outlets,
especially if you intend running both tanks simultaneously - in fact, I'd
say it was essential in those conditions.
If you wire it up with a changeover switch so that only one tank outlet
valve can be live at a time, in theory, one tank can't feed the other. The
only fuel that can get back into a tank under those circs is what's in the
gas line to the vapouriser, which isn't enough to cause problems - I ran one
like this for quite some time without trouble. The only thing that could
cause problems would be a failure of some component or circuit leading to
one tank being open when it shouldn't - however, if you start down that road
you end up triplicating each valve...
The thing about nonreturn valves (which IIRC you canget as single nonreturn
or check valves) is most relevant in the situation you describe with one
tank higher than the other.
--
Austin Shackles. www.ddol-las.net my opinions are just that
"Ask yourself whether you are happy, and you cease to be so."
John Stuart Mill (1806 - 1873)
SimonJ
line, because the LPG in the pipe will have nowhere to go if it expands
while the car is not running, in fact I always thought that the solenoids on
the tank allowed the liquid to flow back into the tank(but not out) even
when switched off, for that very reason. Putting a non return valve in the
line completely removes that safety feature.
The way I piped my RR up (with 4 tanks) was to use 'shuttle valves' in the
connections between all the feed lines, so that the tanks could not fill
each other, but the system could still draw fuel from any tank, and would
still allow expanding fuel to flow back into a tank if necessary.
alex
Now let’s go back to "gas expansion" in feed line. We need hot conditions for the gas to expand, brought up example with heat coming from exhaust contradicting with rules and regulations to fit feed pipes away from exhaust. We can’t talk about gas expansion in feed line while you driving on gas as the gas is in demand status (flowing to reducer), only option is when you stopped after driving and then again I don’t see how the gas will get back into the tank once the feed valve is closed. Here is the question how high pressure could rise in feed pipe from exhaust heat and how many BARs the usual 6mm copper pipe can withstand
(note: on some systems I approached, the outlet solenoid opens this valve by turning the key in ignition to first position, the engine not turning yet, but the valves are already opened, that’s is the problem I think.) Let’s take example: you start the engine, all valves closed, system in standby mode ready to switch over to gas. You accelerate say to 1600rpm and that's when you hear the "click" and the system opens them valves to supply gas, not earlier, that’s in my opinion how good system should work.
May be I’m wrong, but I would like to here your point of view on this.
SimonJ
electric solenoid on it. As far as I know it works this way: if you take the
solenoid off, we will see little tube which incorporates usual valve with a
spring inside which pushes valve down to close outlet permanently. When the
system switches over to gas you hear "click" and the solenoid placed on that
"tube" will pull the valve into UP position, opening the valve so. The valve
remains open as long as 12V supplied to the solenoid, once the 12V supply
interrupted the electromagnet (solenoid) is not capable to keep valve open
and it pushed by spring force to close the valve. I don't see the point of
gas getting back into the tank.
Now let's go back to "gas expansion" in feed line. We need hot conditions
for the gas to expand, brought up example with heat coming from exhaust
contradicting with rules and regulations to fit feed pipes away from
exhaust. We can't talk about gas expansion in feed line while you driving on
gas as the gas is in demand status (flowing to reducer), only option is when
you stopped after driving and then again I don't see how the gas will get
back into the tank once the feed valve is closed. Here is the question how
high pressure could rise in feed pipe from exhaust heat and how many BARs
the usual 6mm copper pipe can withstand
Well I'm not going to claim to be any sort of expert on this subject, but I
can only tell you the instructions I was given when installing the LPG on my
RR.
The tanks have a solenoid valve, which allows gas to flow out when
energised, but when de-energised shut off this supply of gas. I was informed
that they will allow back flow to release any excess pressure in the feed
line due to expansion. Bear in mind that the fuel in the feed line will be
liquid, and as such will be incompressible, so a very small temperature rise
(e.g. when parking a car on a cold morning, and it gets left parked until
the warm afternoon) will amount to considerable pressure rise in the pipe
work. It is therefore quite sensible to allow for this excess pressure to be
vented to the tanks, as the tank will have enough room in them (20% gas) to
absorb this expansion.
Fitting a one way valve will remove this safety feature, hence the reason
for the shuttle valves in the feed lines.
The kit I was supplied with came with these shuttle valves as part of the
kit, I can't see them supplying them if a simple one way valve would do.
alex
never approached them valves and its interesting the way they work.
Regards
SimonJ
> never approached them valves and its interesting the way they work.
>
A shuttle valve is a simple device but also a necessary part of many
pneumatic systems. It is a passive device having no air supply (power
supply) of its own. Shuttle valves are used when signal is required to be
selected from two or more different sources. Also known as "OR" valves, they
allow a signal to pass through from either input A or B (or both) and will
allow the reverse flow of system exhaust through these same inputs. A
shuttle valve selects the higher of two pressures, a function that is to be
considered when designing circuitry.
http://www.kobelt.com/pdf/3009.pdf
alex
My curiousity made me to undo the multivalve just to see how the outlet
valve works. As I described above, when you take coil off, we'll see little
tube which incorporates simple two way valve ( I thought its one way before).
So, when gas leaving the tank under pressure it cant open this valve (the
pressure hits the side of the inner tube-valve, making it impossible to open
it by only applying pressure) Thats when we need coil with electromagnetic
field to pull this tube-valve to upper position, to make clearance inside
the valve to let the gas through.
The outlet "hole" is right at the bottom end of the tube-valve. So, if the
pressure in the pipe line grows bigger than in the tank, it can push this
tube-valve into up position, and make its way into the tank. When the
prressure equalises its closes the valve.
So its works like Shuttle valve in any way.
or maybe I got wrong the idea of Shuttle valve???
Regards
alex
My curiosity made to dismantle one of the multivalves just to see for sure
how it works. disassembled the outlet valve and now can say: that gas can
flow back into the tank ( I was wrong above) but, it requires higher
pressure in the pipe to push tube-valve into up position to allow the flow.
The only question left is: Why we realy need them shuttle valves. If
expansion of gas can go into one tank, why it cant go into both?
SimonJ
"alex" <al...@yoursitenospam.com> wrote in message
news:bdf23e35fad54260...@newspe.com...
There has to be some way of preventing LPG flowing from one tank to another,
otherwise if one tank is mounted higher, (or car is parked on a side slope)
the LPG from the high tank will flow into the low tank, so the low tank will
lose its 20% ullage. This flow can be prevented by having non-return valves
on each tank outlet. But with this method, both tanks are closed off to gas
trying to return to the tanks from the pipe, so could lead to pressure build
up in the pipe.
With a shuttle valve, flow between tanks is prevented, as only one inlet is
open to the outlet at any one time, but because one side is always open, the
excess pressure is allowed back to a tank.