Re: [PSUBS-MAILIST] Isn't 'Mini book review.' anymore--pressure test

[John Brownlee <jonnie@scarymonsters.net>]

	The real issue, I think, is the fact that liquids are (largely)
incompressible. That means that you can take a gallon of water, put it in a
gallon-sized container and with the proper pump create a head on it which is or
arbitrary size providing you can exert sufficient force. The Alvin and other
submersibles with hard water-filled trim tanks use this idea in reverse to
evacuate their trim tank - the pump can move the water from inside the tank to
the outside (ambient) side of the tank against the hydrostatic head, hence
creating a partial vacuum inside the tank. We're trying to run this process
backwards.
	Most of the commercial tanks that are used for pressure testing are
fluid-based. This is for the same reasons they hydro test scuba tanks partially
filled with water - an explosive failure is far less dangerous if part of the
volume is filled with water instead of compressed air, which has an amusingly
high kinetic energy content. 
	I'm less concerned with generating the pressure on a vessel filled with
water, actually, and more concerned with sealing a big tank with a door in it.
Maybe there's some advice to be gleaned on the subject?

					Thanks for the interesing dialogue!

							John

John Brownlee
Chief Systems Administrator
Scary Monsters Network
jonnie at scarymonsters dot net