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.
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.