How to change low-end pressure on Quncy QT/QP compressor?

Hi guys,

I just installed a Quincy QP-5. The pump turns on at ~125 PSI and off at ~175 PSI. I'd like to change the low-end to ~75 PSI, to reduce the number of starts per hour. The release valve that turns the pump on doesn't look to be adjustable, it's a tiny plunger valve with no apparent adjustment. I can adjust the high-end pressure no problem, but I want to lower the low-end pressure.

Are there other release valves for different pressures, or is the 125 PSI valve adjustable? I tried shimming the valve farther from the contact tab on the switch but that didn't change the cut-in pressure.

Thanks, and regards.

Mike

Any help (page 10 ) file:///C:/Users/Mark%20Figes/Downloads/2022201301Jul14%20(1).pdf

and (page 33) file:///C:/Users/Mark%20Figes/Downloads/2022201802Jul14.pdf

Doesn't it have a conventional pressure switch? Like this? http://www.northerntool.com/shop/to...Northern Tool and Equipment&utm_content=16152 If so, cut in/ out is simply set by either adjust of a spring or replacement of the spring depending on the range you want? post pic.. If not, put one on like this example (many many different ranges types available).

In general it's a lot to expect 175 - 75 in ONE differential switch. Usualy they are range contrained. If you can't get the adjustment either by the adjustable spring tention or change of spings, then you can gang two together, the second one one being say 130-75 and put them in parallel.

Here's some Square D switches at Grainger. Note the difference between "range" and "differential" : air compressor pressure switches Water and Air Pressure Switches - Pressure, Vacuum, and Vibration Switches - Grainger Industrial Supply


When you say "plunger".. are you confusing the unloader portion with the pressure adjust? Adjusting the internal spring adjusts when that plunger is activated. i.e., swicth cuts power THEN the plunger unloads the residual cylinder

In my experience the pressure switch differentials are pretty much set, with 40 psi being on the high side. You can adjust the differential tighter but not wider, if it is adjustable. To get a bigger differential you need to spend at least $200 on the pressure switch from what I have found so far. How about a photo of your pressure switch for starters so we have a better idea of what you have to work with. With my well pump pressure switch I found I can shim the differential spring to increase the range. It seems this is what Square D does anyway so I am just doing further adjustments as mine had two .015" washers.

Lakeside53 said:

In general it's a lot to expect 175 - 75 in ONE differential switch. Usualy they are range contrained. If you can't get the adjustment either by the adjustable spring tention or change of spings, then you can gang two together, the second one one being say 130-75 and put them in parallel.

When you say "plunger".. are you confusing the unloader portion with the pressure adjust? Adjusting the internal spring adjusts when that plunger is activated. i.e., swicth cuts power THEN the plunger unloads the residual cylinder

Click to expand...

Probably ... yes .

OK, there are plenty of 100 PSI-differential switches shown at the Grainger link you provided. Would have been nice if the unit came with one like that. Even the POS Home Depot 175 PSI compressor I was using as a stop-gap had a fully adjustable low end, without giving anything up on the top end.

Regards.

Mike.

Thanks for the link Lakeside, I have been needing to get another switch since the unloader port on mine died a few months ago. 30 to 110 psi differential for $105. I just wonder what kind of quality Condor is?

My POS Home Depot compressor will only adjust to a 40 psi differential.

Lakeside53 said:

...then you can gang two together, the second one one being say 130-75 and put them in parallel.

Click to expand...

If they are just parallel-connected, the compressor will kick on at the cut-in pressure of the HP switch. IOW, it won't accomplish what the OP wants.