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Re: overpressurized regulators

Tim sez:
> I have stated this before, but it warrants repeating.  You have to look 
> at your entire pressure circuit and determine your weak link and make 
> sure you are adequately protected.  Installing a "cheap low-pressure" 
> regulator downstream of a high pressure source is very dangerous.  Most 
> cheap low pressure regulators are typically only good for 150 psig or 
> less.  A diaphram failure in the high pressure regulator is a very 
> feasible event.  860 psig is enough pressure to impart significant 
> velocity to regulator fragments........
> Again I strongly recommend that you understand your design pressures, 
> people have been killed  by overpressurized regulators coming apart.

That's a good point.  The failure mode that I've most often seen is not
a diaphram failure, but where the regulator leaks just a little from the
high side to the low side -- so at extremely low flow rates the output
pressure drifts up, bounded only by the cylinder pressure.  It would be
cheap enough to either use a rubber hose between the two stages
(presumably the hose would fail safely long before the 2nd stage
regulator), or install a pressure relief valve that would blow at, say,
150 PSI.  Pressure relief valves are cheap and compact and reliable.  It
could be screwed directly into the first stage regulator body in place
of a low-side gauge.

If you use an old acetylene regulator for the second stage, check with
the manufacturer and see what its maximum inlet pressure is.  It might
surprise you.  The gauge will only go up to 400 PSI, but most Victor
regulators (even acetylene and LP gas) are rated for 3000 psi.  So you
would not need any overpressure protection. But be careful; I have one
"Firepower" regulator made by Victor that is only rated for 400 psi.

Best regards,