I've been researching this for quite a while and feel somewhat exasperated, so I thought I would ask more knowledgeable folk. I need to seal a closed system for low vacuum, and I need to do it on a budget. My problem is that most of the information I have found deals with much higher vacuums (10-6 torr) and the systems are continuously pumped. I just want an adequate solution, not overkill. Problem Definition: I am trying to make a small apparatus that demonstrates heat pipe operation using water. The system would have two chambers -- for evaporation and condensing -- connected by copper tubing. Both chambers will have glass windows so the boiling/condensing can be seen in action. The primary problem is sealing the glass windows to the chambers, but I will take advice on all other aspects as well (tube to chamber, valves to seal from vacuum pump etc...). I want the seal to last a while, so the demo unit can run without constant maintenance. The lowest pressure I will have to seal against should be 9 torr, the vapor pressure of water at 10° C. I expect the system to run well within 9-150 torr (i.e. H2O vapor pressure 10-60° C). Questions How to seal the glass to the aluminum/copper chambers? (elastomer o-ring, epoxy, indium,...) How to seal copper tubing to Al/Cu chambers? (compression fitting, solder, epoxy) How to remove vacuum pump? (needle valve?) I am thinking epoxy might work for joining/sealing the glass, due to the information I found in this thread. I can machine the parts I need (chambers), but for obvious reasons off-the-shelf solutions are preferred. Thanks!