http://www.armadilloaerospace.com/n.x/Armadillo/Home/News?news_id=198
> We put the cabin on the other side of a concrete wall, and > started bringing the pressure up. At 17 PSI...
From other context, this sounds suspiciously like a pneumatic test, not a hydro test. This is a Very Bad Thing To Do, since the energy stored in a pneumatic system is far far higher than in a hydro test. To a first approximation, the energy is P * V for gases, so your ~2 m3 cabin at ~120000 Pa had over 200,000 joules stored. If this lets go, even behind a brick wall you and all the windows in the neighborhood will regret it...
Your cabin is small enough that you can ignore the hydrostatic head, and not put the test article into a swimming pool to cancel out hydrostatic pressures. (This is a major consideration for testing large low pressure vessels like space station modules, and is why they are hydro'd in a pool.)
17 psi isn't an adequate test anyway- the standard is to test to 1.5x use pressure, which would be more like 24 to 26 psi. Maybe you should treat this first cabin build as a mockup and structural test article, test it to destruction, then build a flight cabin incorporating lessons learned... and hydro that cabin to 1.5x use.
I hope the orifice and back pressure regulator system work well for you. Perhaps you could connect a vacuum pump to the vent port to verify that it operates as we think it should.
Doug
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