Building a Vacuum Filling System: Valves & Fine Leaks

[Adi Wijaya]

I'm building a vacuum filling system for charging liquid inside heat pipe. I am using 1/8 inch stainless steel tubing for system connecting construction and swagelok ball valve 1/8 inch for regulating the pump down flow from heat pipe to vacuum pump. The fluid regulate with micro metering valve. The goal of my vacuum pressure around 0.1 pascal but until now I could not reach that level due to many fine leaks. Unfortunately my ball valve could not stand for the vacuum condition because there is no o ring inside the valve. Also I using 1/8 inch tee swagelok for connecting three stainless steel tubing and this could be source of the leaks.
Question
What valve should I use for this application which still affordable with my budget
How can I minimize the fine leaks so when I turn off the vacuum pump the vacuum pressure still stable for hours so I could have enough time for injecting the fluid?

Thanks a lot

 

[gleem]

Regarding the Swaglok fitting, do you finger tighten the fitting then use the standard 1-1/4 turn tightening procedure? also your 1/8" tubing may not be round enough or have a too irregular surface to get an adequate seat.

I seem to remember seeing a ball valve used with a backing pump (although not as small as yours) so maybe you just chose the wrong brand. I think you can get vacuum rated manual valves with "O" ring seals but I do on think that they are made as small as you would like. Unless you have a method of locating the leaks you will have a hard time dealing with the problem.

 

[Adi Wijaya]

Thank Gleem
Yes, I already tighten the fitting correctly...yes It's difficult to find the valve suit with the 1/8 inch tube...I guess I should change to bigger tubing

 

[OldYat47]

Swagelok makes many valves in 1/8" size that can do vacuums just fine. Check the Swagelok catalog or call the local dealer. I've used Swagelok products in numerous applications, both vacuum and high pressure. Assembled correctly you should have no problem achieving 0.1 P.

 

[Adi Wijaya]

Swagelok makes many valves in 1/8" size that can do vacuums just fine. Check the Swagelok catalog or call the local dealer. I've used Swagelok products in numerous applications, both vacuum and high pressure. Assembled correctly you should have no problem achieving 0.1 P.

Thanks a lot OldYat47
I'm already contact the local dealer for the solution, they proposed Stainless Steel High Purity High Pressure Diaphragm Sealed Valve, 1/4 in. Swagelok Tube Fitting, Lever Handle
http://www.swagelok.com/en/catalog/Product/Detail?part=SS-DLS4
but the price more thank twice from my current valve (ball valve). I've been check my ball valve, that the leak came from the under the handle. When I've turn the handle to shut off the valve, my pirani gauge directly shows rapidly decrease vacuum pressure, I note it around 100 pascal.
If you don't mind my I know the right valve for this application (0.1 Pa)?with the reasonable price or I should change the tubing with 1/4 inch? Thanks a lot again

 

[sophiecentaur]

A solder plug could be a cheap solution. Evacuate the tube and then melt a lump of solder, inside the tube (a U). It would be cheap. Or perhaps a thermoplastic plug.