Do i need a unloader valve on my switch?

i have a presser switch with out unloader valve do i realy need a unloader valve

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Oct 01, 2017
Pressure switch without unloader
by: Bill

Hi Tom...

If you visit Square D Pumptrol Water Pump and Air Compressor Pressure Switches you can find them without unloader valves.

See: http://schneider.thomasnet-navigator.com/

Sep 30, 2017
No unloader valve on shutoff switch
by: Tom Curler

Dear Bill,
I have a 30 gal Montgomery Wards, 230 volt air compressor that I purchased new in the mid 70's. The original pressure switch (manufactures) does not have an unloader switch, nor does the compressor have any plumbing to add one. Every replacement switch I can find has an unloader valve. What is my solution to replacing the pressure switch?

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compressor restart issues

by Doug

I have a Mastercraft 4 gallon air compressor. If the tank is totally empty, the unit will operate to the safety cutoff pressure. As the pressure declines with use and reaches the cut-in pressure level, the unit attempts to restart but does not restart.

I think this is a pressure switch issue, but I am not sure. Thoughts??

Thanks for your advice.

______________________
Bill says...

Hi Doug. When you say... "the unit will operate to the safety cutoff pressure. " I read that to mean that the compressor shuts off at the normal cut out pressure. If, in fact, it runs until the PRV valve blows, then yes, I'd suspect your pressure switch.

However, you also say "If the tank is totally empty, the unit will operate to the safety cutoff pressure." and that, to me, points to the Unloader Valve being the problem.

Check out the valves page and click the link to the Unloader Valve for more info.

Cheers,

Bill



Comments for compressor restart issues

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Feb 01, 2017
Hard Starting
by: Splitshaft

I think the obvious might be overlooked here. It takes a lot of electric current to start an air compressor motor with or without an unloader valve.

With an empty tank, the motor can start and run almost free and draw very little current. As air pressure builds gradually, so does current draw. Even with an unloading valve (no head pressure) the compressor will start pumping in very short order against the cut in pressure in the tank. The electric current (surge) draw when starting at cut in pressure is much greater than when the tank is empty.

If possible, try plugging the air compressor in closer to the service entrance panel of the building. If it is a small 115 volt compressor, try plugging it into a 20-amp circuit closer to the service entrance panel or any 20-amp circuit over only a 15-amp circuit. If the compressor then starts at the cut in pressure, the circuit serving the compressor motor has too much electrical resistance or voltage drop (loss).

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Compressor hums and blows the breaker

by John
(Milford ct)

I have a devilbus 20 gal 5 hp oil less

Comments for Compressor hums and blows the breaker

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Oct 01, 2017

by: Bill

Hey John, nice to hear from Milford. Was near there a few weeks ago on the way to the Cape.

Please visit the Unloader Valve (use sitemap or follow link from Valves page) page, and have a read.

I think that your unloader valve isn't working, this adds too much load to the motor on re-start, and this blows the breaker.

Thanks for popping in.

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