Air compressor learning experience redux

[dpb]

I mentioned in a thread couple-three weeks ago "Learning Experience" that a compressor kept running owing to relief valve failure that I'd had the one here not cut off at pressure...

So, finally got new pressure switch and it acts same way...anybody think of a reason the switch doesn't drop out at cutout pressure?

This is brand new switch as I just figured the old one had konked and the contacts didn't look great and had 30+ yr service so hadn't done any real looking at the switch itself.

The inlet pipe is not plugged, the air pressure drops and it will kick in in synch with the gauge but just keeps on climbing past 125 cutout when running...

Got me baffled...

[Clare Snyder]

Mabee it's set to 126 - or 150 - Try resetting the pressure (or check your gauge - it may be reading low)

[dpb]

Actually, if it is the gauge it's reading high when supposed to cut off and dead on at cut in...switch says is 95-125 and it's well past 130 and still running when on but will cut back on when drop pressure to indicated 95 (within a couple w/ resolution of gauge).

But, the baffling isn't quite so baffling -- after supper went back out and adjusted the cutoff back a little--and it now cuts out where should...

Will have to get another gauge to check whether the present gauge is really off or not altho didn't take much adjustment so I'm guessing it's pretty close and the switch just has a little more than nominal hysteresis between close and open points. This one is a little different than others I've seen -- has a screw supposed to only change cutout and the normal one that changes both. I'd not seen the former before...then again, first one I've had to swap out in almost 30 years...they generally last the life of a tank or compressor in my experience.

[Clare Snyder]

Every one I've had to work with since about 1969 had dual adjustment

- one screw for low pressure cut-in and one for high pressure shut-down. Set wrong you can have a compressor that sounds something like a machine gun------ At the shop we usually had them set at 95-150 so they weren't cutting in and out so often - and at 150 an old CP734 impact had some SERIOUS power.