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>     The simplest method I've heard of was explained in the 1972 US Diver's
>     service manual.  That manual said that if a magnahelic (sp?) is
>     unavailable, the technician can submerge the 2nd stage under 2" of
>     water, at which point it should crack.  However, I have never bothered
>     to do the math to see how many mm Hg equals two inches of water.

You can also make a quick and dirty suction gauge from length of
transparent tubing bent into a U and secured to a board - electricians
romex staples work well - mark the space between the two columns in inches
or cms according to taste, fill the sump with water, and read inches/cms
water by comparing the difference between the two columms.
I've go one I use both to play with regs and to check airspeed indicators
on aircraft with.

The catch is, with both the above gauge and the basic reg test benches,
cracking pressure without flow doesn't really tell you a hell of a lot
about how a reg will perform at depth. The better panels have a built in
flow tester (basically a suction pump/blower with a flow gauge, so actual
output at various cracking/suction pressures can be measured.

BTW, the main difference between a reg test bench and a couple of loose
gauges is that the test bench usually has a regulator so that the input
pressure to the reg 1st can be changed with a twist of a knob rather than
by looking around for a tank with the right pressure in it. These regs are
very expensive all by themselves, and contribute a lot to the cost of a
panel. It does make it a lot easier to test valves, since you can screw the
valve into the adaptor, and pressurize it without having waste a entire
tankfull of air.




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