I seem to be having an issue with my little vacuum chamber I am building where I can only reach a base pressure of 6,000mTorr which is pretty high and am trying to figure out what is wrong. I have a new, clean viton gasket; a brass base plate, I have tried thick plastic and glass chambers. All the ports are sealed with either teflon tape and/or dow corning vacuum grease. I am using just water valves with the internal ball and rubber seals to vent or pump the chamber.
Any suggestions on what is wrong?