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[W. Mark Hellinger]

The Square D switch should work with either medium (water or air). In fact, in most water well pump scenarios the pressure switch is actually measuring/sensing the pressure of the air bubble in the tank bladder and is not in contact with liquid water.

Been there and inadvertently tried that... and learned well enough to commit it to active memory an important aspect in what I surmised is fundamental difference between well pump and air compressor pressure switches, being:  The air compressors models have a pressure relief valve that dumps the compressor's cylinder pressure at the end of the recharge cycle... hence the "per-choo" when the air compressor motor shuts-off.  The well pump pressure switches have no such thing it seems.  So if one puts a well pump pressure switch on a air compressor (as I did a number of years ago), the panel breaker and/or over-load button on the motor would commonly trip on restart, especially if the compressor had recently been run (in my case anyway).  I went around and around on this trying to figure it out thinking first maybe I had a bad cap on the motor... changed all three of those out/no difference.  Then figured maybe the start winding weren't consistently engaging... but nadda there either.  Then changed motors... nadda.  Then dismantled and inspected all aspects of the compressor and reassembled with new wear parts... no difference.  Then changed compressors... no difference.  Upgraded all wiring to heavier gauge, no difference.  Finally I re-geared the compressor speed to run slower to put less of a load on the motor by putting successively smaller pullies on the motor... finally at about 1/4 speed on the compressor, that solved the start-up stall... but it builds pressure really slowly... but WORKS reliably... and truth be known: probably kept the years later unattended line rupture situation from going-up in a fire-ball.  And it was only by coincidence that I noticed another air compressor did that "per-choo" thing at the end of the pump-up cycle and I got to thinking:  "Hey, my air compressor used to do that... why not now?"  Oh... wrong type of pressure switch... duh... learn something new every day.  So last weekend I was clearing out some boxes of "vintage" hoarded collections... and found the compressor applied well pump switch I'd kept to remind to get a compressor switch with the low pressure shut-down like the well pump switch... which moved me to action per "if not NOW, then WHEN?"... Which ultimately lead me to starting this thread.

[Russell Ault]

{...} Maybe an electronic solution would work.  ie, the pump is only allowed to run for X number of minutes per hour or it trips off, requiring a manual reset.  If you happen to be using the compressor excessively in that hour, it's a minor inconvenience, but at the same token, maybe the compressor will need a rest anyway. {...}

I like this approach. In theory you could even go a step further and set up actual thermal protection for the motor (i.e. some kind of thermostat), but limiting duty-cycle is probably the easier and simpler mechanism to implement while still covering partial failure modes.

-Russ

[Steve-White]

I like this approach. In theory you could even go a step further and set up actual thermal protection for the motor (i.e. some kind of thermostat), but limiting duty-cycle is probably the easier and simpler mechanism to implement while still covering partial failure modes.

-Russ

If it's a larger compressor setup with a magnetic switch this would be an easy addition.  An adjustable timer would be the best option hands down.  You could set it up based upon usage and if needed adjust as required.  You could even set it up with a drop-out relay so once it faults things shut down requiring a manual reset.

[ProSoundWeb Community]