Connector from glass to vacuum system

[jb-electronics]

Hi folks,

I received my needle valve yesterday and improved my vacuum system. It
works nicely: I can evacuate the system down to about 0.01 mbar and then
use the needle valve to let in well-defined amounts of Neon. I can
easily adjust the pressure inside the system in steps of 0.1mbar which
is more than sufficient. See my current setup here:

http://www.jb-electronics.de/tmp/vacuum_system.jpg

But there are some minor leaks, mainly caused by the rubber hose
connectors that I use: I still have to figure out a proper way to
connect my 8.8mm tubing to the KF16 flange system; right now I am using
an ordinary rubber hose as seen in the picture. Does anyone know how to
build or get a proper pump union? Just like here, but with a flange adapter:

http://www.teralab.co.uk/Glass_Blowing/Pump_Unions/Pump_Unions_Page1.htm

I do not have a lathe at my disposal. Also, the connection between the
pressure reducer and the needle valve is not optimal. Any suggestions?

Thanks
Jens

[David Forbes]

Jens,

I think it would be possible to drill the needed hole in the fitting
using a drill press. The o-ring does the sealing work, so the hole does
not have to be perfect. You can make the chamfer with a large
countersink bit.


--
David Forbes, Tucson AZ

[Dalibor Farný]

Hello, nice!

Are You sure the valve above the pump is vacuum tight? I guess it is ball valve, I would look for the leaks here. Keep the rubber joints as short as possible (try the glass tube almost touching the metal inside the hose), that is because the rubber permits some amounts of gases inside through its wall, search for "vacuum permeability). But rubber is far better than silicone. If You have a high vacuum grease, coat slightly the glass tube and metal tube before joining. Did You try blanking the flanges for neon and tube (only the pirani will be present), just to make sure the system is leak tight?

Dalibor Farný
http://dalibor.farny.cz

sent from Samsung Galaxy Pad

Dne 28.10.2012 17:36 "jb-electronics" <webm...@jb-electronics.de> napsal(a):

--
You received this message because you are subscribed to the Google Groups "neonixie-l" group.
To post to this group, send an email to neoni...@googlegroups.com.
To unsubscribe from this group, send email to neonixie-l+unsubscribe@googlegroups.com.
For more options, visit https://groups.google.com/groups/opt_out.

[glasslinger]

Hello!

You most likely have a serious leak in the ball valve. You might get temporary seal in it by disassembling it and packing the seal areas solid with vacuum grease. This would be temporary and subject to begin leaking again at any time but could give you a few days of leak free operation without changing out the valve to a better one. You would do better to get a hardware store water valve with a standard packing that you could remove and replace with a teflon plug packing. I have done this and made valves that are tight to 10 -6 torr! Be sure to get a "plug" valve and not a gate valve. (a plug valve rams a rubber plug onto a seal surface. A gate valve slides a metal gate into a groove.)
You should not have any problems at all with the rubber hose in those short sections so long as you use grease on the connections. Permeability of the rubber is minimal at room temperature and would take hours to affect the vacuum at the pressures you are using. How long will the pressure stay constant when you turn off the power and close the ball valve? It should remain below 100 microns for several hours if you don't have a leak. Important: Note that to outgas the system to do this test it will take about 4 hours of continuous pumping regardless of leaks! (surprise?!) Yes, it takes that long if you cannot heat the system a bit with a torch or heat lamp! Most new users in vacuum are very surprised at how long it actually takes to outgas a system that has been at atmospheric for any length of time! You may not have a leak, just normal outgassing!
Just out of curiosity, why do you need such a close control of the neon into the tube? For nixies it surely isn't necessary. What are you going to make?????
glasslinger

[jb-electronics]

Hello all,

a friend of mine will supply me with a suitable adapter for 9mm glass
tubing. Really amazing! I actually found some at ebay for $20 or so as
well, the company Swagelok makes them (among others).

Thanks for drawing my attention to the ball valve. I checked, and as it
turns out it has been made for high vacuum applications, so I am
confused why it should be the source of the leak. Maybe there is no real
leak and it is just outgassing:

I need to get some vacuum grease and recheck the system after some
longer evacuation time, so thanks again for the hint, Dalibor and Ron!
Once I have re-greased the flanges I will leave the system running for
some time and then check the pressure.

Regarding the needle valve: I wanted a reliable valve that allows me to
adjust the neon partial pressure very accurately, because later on I
will also use this valve to let in argon (very low partial pressure) and
then fill up the rest with neon to create a penning mixture. For this
procedure I need an accurate valve. Granted, it might have been possible
to save a little money on this one, but I am not the craftsman to build
something like that by myself, so I took the shortcut of purchasing a
slightly overengineered valve. But then again, I only have to buy it once.

There are many ways to a well-working manifold. I chose the way of using
KF16 flanges for all parts, while others might find it more convenient
to build components on their own. But I really want to focus on
tube-making and not on building a ton of equipment which just takes too
much time for me.

But then again, it is up to everybody's personal habits and abilities.

Jens

> --
> You received this message because you are subscribed to the Google
> Groups "neonixie-l" group.
> To post to this group, send an email to neoni...@googlegroups.com.
> To unsubscribe from this group, send email to

> neonixie-l+...@googlegroups.com.
> To view this discussion on the web, visit
> https://groups.google.com/d/msg/neonixie-l/-/1wVGl-JG6gQJ.

[Dalibor Farný]

Hello Jens,

You are definitely right with dosing the argon, there must be around
0.5% of argon and with pressures about 30torr we are talking about
really really small amount of argon.. Where did You get the valve from
and how much does this cost? I am considering building one myself, but I
am afraid of wasting time and money on it and eventually buying a real
one :-D

Thanks!

Dalibor


Dne 30.10.2012 23:35, jb-electronics napsal(a):

[jb-electronics]

Hello Dalibor,

my valve comes from Leybold, see here:
http://www.ld-didactic.de/index.php?id=ld-artikel&a=378776

With 240 EUR it was rather expensive, but it is the best valve I have
found. Also, I got my whole vacuum equipment for free from a friend of
mine here in Germany, so this is all I paid.

By the way, this is the ball valve:
http://www.ld-didactic.de/index.php?id=ld-artikel&a=378777&L=0

Jens

[jb-electronics]

Hi again,

I made some tests with my vacuum system today: I opened the ball valve
and let the pump run for two hours straight. After about ten minutes,
the pressure arrived at 9E-3mbar and stayed there for the rest of the time.

I heated my flanges with a hot air fan for about five minutes, but the
pressure did not change at all. So I guess this means that there is not
so much residual material left on the inside?

During these two hours, I closed the ball valve and left the pump
running. The pressure increased to 0.1mbar in about 3s and to about
1mbar in 30s. After opening the ball valve, the pressure went back to
9E-3mbar in 5s. I repeated this experiment several times, always with
roughly the same results.

After the two hours I shut off the pump and closed the ball valve. The
pressure rose from 9E-3 mbar to 1mbar in 10s (really fast) and to 4mbar
in about 2 minutes. After 10 minutes I had 100mbar or more.

So there appears to be a leak, this cannot be mainly caused by
outgassing, can it?

Jens

[NeonJohn]

On 11/01/2012 11:17 AM, jb-electronics wrote:
> Hi again,
>
> I made some tests with my vacuum system today: I opened the ball valve
> and let the pump run for two hours straight. After about ten minutes,
> the pressure arrived at 9E-3mbar and stayed there for the rest of the time.

Jens,

When I was building my metal neon manifold (and later when I started
making them for others), I experimented with just about every valve
format I could get my hands on. Rule of thumb is, if it has packing it
will leak vacuum.

My solution was refrigeration diaphragm valves.

http://www.neon-john.com/Neon/Shop_equip/Metal_Manifold/Metal_Index.htm

This type of valve transmits the force of the closing stem through a
stainless steel diaphragm to the actual valve mechanism. There is no
packing to leak. The only minor downside to this type of valve is that
it has a small bit of polymer in its seat. This absorbs moisture when
the system is at atmospheric pressure. Under vacuum it takes about a
day to outgas.

You'll notice a couple of packed needle valves on the gas metering part.
I could get away from that by putting the SEAT toward the vacuum and
the packing side toward the always-pressurized neon and argon sources.
Plus those are nuclear grade double-packed valves.

John


--
John DeArmond
Tellico Plains, Occupied TN
http://www.fluxeon.com <-- THE source for induction heaters
http://www.neon-john.com <-- email from here
http://www.johndearmond.com <-- Best damned Blog on the net
PGP key: wwwkeys.pgp.net: BCB68D77

[glasslinger]

Hello!

Look carefully at what you described. The ball valve is the culprit, rated for vacuum or not. If the valve is closed, there should be no effect on the pressure if you shut off the pump. Also, as John below says, the packing in those valves is highly suspect. The only packing I have found that will hold a perfect seal is a compressed teflon plug onto mirror polished surfaces. Anything else will dry out and leak. You could try re-lubing it with good vacuum grease, but that will only be a temporary fix. To truly have a leak proof system you will have to change out that valve it looks like. You can find a high vacuum bellows sealed valve on ebay for a lot less than you paid for the needle valve!

ron

[jb-electronics]

Hello Ron,

I will keep looking for a more suitable valve, but in the meantime I will try to fix it with some grease to see if that changes anything.

Do you have a recommendation for some valves with flanges?

Jens

Hello!

Look carefully at what you described. The ball valve is the culprit, rated for vacuum or not. If the valve is closed, there should be no effect on the pressure if you shut off the pump. Also, as John below says, the packing in those valves is highly suspect. The only packing I have found that will hold a perfect seal is a compressed teflon plug onto mirror polished surfaces. Anything else will dry out and leak. You could try re-lubing it with good vacuum grease, but that will only be a temporary fix. To truly have a leak proof system you will have to change out that valve it looks like. You can find a high vacuum bellows sealed valve on ebay for a lot less than you paid for the needle valve!

ron

--
You received this message because you are subscribed to the Google Groups "neonixie-l" group.
To post to this group, send an email to neoni...@googlegroups.com.
To unsubscribe from this group, send email to neonixie-l+...@googlegroups.com.

To view this discussion on the web, visit https://groups.google.com/d/msg/neonixie-l/-/97AX8xIzEIkJ.

[Dalibor Farný]

Does your pump have a system what prevents the oil to be sucked back into vacuum aparature when turned off? If so, you can try removing the valve and measure the vacuum after turning the pump off.. it should hold the vacuum.

And did You try to unmount all the branches from your aparature except the pirani one? This would eliminate possible leaks on other parts of system..

Dalibor Farný
http://dalibor.farny.cz

sent from Samsung Galaxy Pad

Dne 2.11.2012 18:39 "jb-electronics" <webm...@jb-electronics.de> napsal(a):

[jb-electronics]

Hi Dalibor,

yes, the oild does not just simply get sucked back, there is a protection. I actually tried what you said about three hours ago, and as it turns out, it also leaks with no ball valve and the pump turned off.

But I should mention that there is almost no vacuum grease on some connections. Will re-grease them in a couple of days (when the grease gets here) and try again then. In the meantime, I will keep my eyes open for a different valve.

I will also mount the Pirani and nothing else tomorrow and see if I get the same results.

Jens