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Re: Pressure Regulator

Casey thinks I'm wrong about how a pressure regulator works.  It is certainly true that I've never studied the mechanical details.  But from an experimental standpoint, I stand by my statement that as the inlet pressure decreases, the outlet pressure increases.

Perhaps I should clarify my statment about the regulator becoming an open valve.  For a given setting of the adjustment screw, a lower inlet pressure will result in a higher "set" point for the outlet pressure.  Eventually, as the inlet pressure decreases, the set point will exceed the inlet pressure.  At that point, the diaphragm stays open, and the regulator is an open valve.

Assuming that what you have downstream of the regulator is effectively a flow restriction device (be it a sintered glass diffuser, needle valve, etc.) the flow will increase with the square root of the outlet pressure.  This may be hazardous to your fishes' health.  Furthermore, if the hardware that you have on the downstream side can't handle the additional pressure, you could be in for even more trouble when, for example, the airline tubing pops off of the nipple.  

Of course, the other possibility is to have a second pressure regulator downstream.  I've never dealt with a dual stage regulator personally, but assuming that it is effectively two standard regulators in series, decreasing the inlet pressure will increase the inlet pressure to the second regulator, and actually *decrease* the final outlet pressure.

David Ozenne
Fremont, CA

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