I would like to pressure test a closed hydronic radiator system that has an expansion tank on it. I can detach the furnace, shut the water supply, and then mount a gauge with a nozzle on it that I can pump to something like 15-20 psi of compressed air and hope it keeps the pressure, meaning no leaks. I've done that with my gas pipes before successfully.
I am only concerned about the expansion tank. Should I remove it and put a plug in its system socket, or can it withstand that kind of pressure? I'm afraid of it exploding.
Best Answer
Check the rating on the expansion tank, but I'm almost certain it would be able to withstand 15-20 PSI. But I'd still remove it and here's why. If you have a slow leak, the expansion tank would act as a buffer (add volume), to your system. This would make any loss of pressure much slower, perhaps to the point where you didn't realize you have a leak.
Is there a reason you don't want to use water to test? Water doesn't compress and any leaks would result in rapid pressure drop. You'd have to control for temperature variations but over a few days, you'd know if you had a leak.