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Vacuum chamber leakage

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Mr-Pooman

Mechanical
Feb 7, 2022
8
GB
I have built a homemade vacuum chamber with the intention of developing a reliable vacuum of 1 Pa to 5 Pa, however when I isolate the pump the pressure rises by 100 Pa in 5-10 minutes and then the rate tapers off to insignificant rise after 24 hrs approx; between 900 Pa to 2,400 Pa (similar to mass damper system cure). At first, I thought that this was due to degassing, but I get the same result when I restart the pump hence the difference in the final pressure. The vacuum pump I am using can only develop 500 Pa and that is another issue, but I don’t think that should change this problem. I am looking for tips/advice on what I am doing wrong and how to improve it. Details of the construction are below.

Vacuum chamber from 8” PVC pipe, with stub flanges fixed with a PVC cement. The ends are 20mm acrylic, with a 3mm thick solid rubber C40 rubber seal. There is currently a single port in one of the acrylic ends, made from 15 mm dia copper pipe (standard central heating pipe) which is fix in place with super glue and with a twin pack epoxy forming a boss on both sides. The port is connected to the vacuum pump via a double ball valve cross with mechanical gauge from a commercially available vacuum chamber set. The two are connected by John Guest Speedfit style elbow, but 3D resin printed with space for 2 and 3 o-rings. Pressure measured by a Adafruit pressure sensor over Bluetooth.
 
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I imagine The components were glued and assembled atmospheric pressure.
Applying vacuum distorts things a bit, especially flat panels .
Lots of joints to potentially leak.
How sure are you the isolation valve is up to the task?

Supposedly Loctite wicking 290 may good to e -8. It may not be compatible with some of your materials though.
A few drops of 290 on each joint with the chamber at fill vacuum might seal things up, almost permanently.

I'd probably apply the 290 to one joint at a time while watching the vacuum gage. The info about particular joins would be helpful building chamber 2.0.

 
Thanks Tmoose the wiki page very use and it looks like I've used all the wrong materials.
 
I wonder if there "paints" that that can reduce material outgassing?
 
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