My air compressor doesnt shut off when it reaches 125psi like it should??

by Jason
(Grand Blanc Mi)

It should start at 90psi and shut down at 125psi. It just continues to run and I do not know why?? When I mess with the switch from off to auto it did breifly stop yesterday but after another switch up and down it again started to run and will not stop??


Does anyone know what could be causing this? How can it be fixed? Also my compressor is a Coleman Black Max 27 gallon 5hp oiless compressor verticle style.

Does anyone know where the air filter is located?? Shouldnt it be cleaned/checked or changed from time to time?? Any answers would be great. Thanks






Hello Jason...

What happens when your compressor doesn't stop? Does the pressure relief valve pop open?

Regardless of that, it sounds like your pressure switch is pooched.

The pressure switch senses the pressure inside the tank and when that pressure reaches the set point, it both shuts off electrical power to the motor, and unloads the air compressor.

If this isn't happening, then you may "enjoy" a catastrophic failure of your air tank. Get it fixed.

As to the air filter, your compressor will have an air intake port up around the top of the compressor head. Usually it's got a black plastic doo-dad screwed into it and there will be a hole in the bottom of this into which free air flows as the compressor works. That air passes through an intake filter inside the plastic housing before it gets to your cylinder.

That unit can be unscrewed from the compressor head, the cover should pop off, and the filter inside can be examined and, if necessary, cleaned.

Bill

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Nov 22, 2008
Reply 2
by: Jason

If I leave it running it will release the air but I turn it off just after it hits 125 so It doesnt happen much. Inside the pressure switch I noticed that the issue is the plastic lever does not trip anything when I switch it from auto to off. It looks like the inside of the switch box has been pulled out and its out of position which is causing the plastic lever not to change anything when it is flipped. If I cant fix that, where and how much is one to buy?






Yup, it sounds like the pressure switch unloader valve toggle is broken.

I don't know where you are...but if you Google compressors parts or compressor repair shops and your town, you should find a local source.

Might be an idea to take the one you've got with you when you go to the store. It were me, I'd take great pains to use masking tape to label which wires were connected where, and even take a
few digital pictures of how this one was installed so you could replicate the installation of the new one.

Cheers,

Bill

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Pressure switch problem with my Cummins 1.5hp air compressor

by Melvin
(grand coulle WA )

Parts came apart inside off and on switch like spring and connectors.






Bill responds...

Hi Melvin, and thanks for sending in your comment.

Since I don't have a photo of your problem, and there really isn't a question here, I'm guessing that you are inquiring about spare parts for your compressor on/off switch?

That being the case, the first thing you should do is contact your local Cummins office for information.

You have one here:

CUMMINS NORTHWEST, LLC
173 Hamilton Rd, CHEHALIS, Washington 98532-1813, United States
Phone:(360) 748-8841
Fax:(360) 748-7015

Before you contact them, gather as much information about your compressor as you can. What HP is the motor, is there a model number, and serial number etc. The technical people will need that information in order to zero in on the correct part for your air compressor.

If that doesn't help, go to the Nav bar and click on the "Repairs" button, and see if there is a compressor repair depot near you that might be able to offer a different brand switch that will still work for your unit.

Could you let us know how this turns out?

Thanks,

Bill

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When demand for air is high the pressure switch doesnt kick on properly.

by Kevin Karwat
(Reese, Michigan USA)

I replaced the pressure switch and after a couple of hours of use the switch did not engage and allowed pressure to run down thus shutting my machines down.






Bill replies...

Hey Kevin, nice to hear from Reese, Michigan.

A pressure switch is a (although complex to make I would think) a pretty simple device.

It's got a set of points inside that, when closed, allow electricity to flow to the motor.

When the pressure in the tank drops to the cut-in pressure, the spring overcomes the resistance from the air, and closes the points, and your electric motor starts. That's pretty much how they work.

If the pressure drops past the cut-in point and the points close, then electricity flows, and if the motor doesn't start at that point, then it's probably a capacitor or motor problem.

After you changed the pressure switch, were the cut-out and cut-in pressure levels correct? Did the compressor always start when the pressure dropped to the cut-in pressure level?

You mentioned that it ran for a couple of hours of use then failed. During that two hours, was the operation flawless?

Can you get your compressor running at all?

If so, then before you start it, very carefully (when the circuit is live the points will be exposed. You can kill yourself if you aren't careful) pull the cover from the pressure switch, turn on the compressor, and watch what happens when the pressure in the tank reaches cut-out pressure. Do you see the points shift to cut off the electricity flow?

Now, open a line and bleed down the tank well past the cut-in pressure. If you don't see movement in the points then it's likely the pressure switch...again.

If the points move, then you have to look at the capacitor or motor for your problem.

Cheers,

Bill

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Air compressor won't throttle up?

by Cooper Reese
(Taji Airbase, Iraq)

I have a Yanmar diesel with an Ingersoll rand tank and compressor mounted to a trailer for portability.

The team works fine together until the air gets real hot.

At that point, the engine stays at idle and sounds as if it is going to choke down at any second.

I am an aircraft mechanic. I know nothing about air compressors other than how to hook an air tool up to one.

There is an actuator coming from the the relief valve mounted on the tank. The actuator is linked to the fuel control on the engine (it sits beside the motor on this trailer).

Like I said, it works fine for 10-15 min, then after it heats up good, the pressure barely makes it to 70psi (normally 140-150 easy) and it takes forever to get up to that pressure (at start up, normally 30 seconds and the tank is full)

I have no idea what models these tanks and compressors are at this time.

Any idea as to what is going on wrong?

Any help will be great.

Only bad thing is, I am in Iraq as a civilian and the availability of hardware stores are slim right now....

Cooper






Bill answers...

Howdy Cooper, very nice to have you visiting my site from Iraq.

Trying to diagnose a compressor problem from afar would be tough enough for a compressor mechanic, and it's even tougher for me since I'm not a mechanic.

So, what's getting hot? The air in the tank, the compressor itself, the diesel engine?

It sounds like your system is using a pressure bleed from the PRV to modulate the operation of the diesel.

The actuator presumably shifts one way when the pressure in the tank is low and this opens the throttle on the diesel to generate more air? Then as the pressure of the compressed air in the tank increases, that shifts the actuator again, reducing the speed of the engine. I'm just guessing here.

It sounds like when it gets hot the temperature is negatively affecting the operation of that throttle mechanism, and as you say, “ the engine stays at idle and sounds as if it is going to choke down at any second”.

That would suggest to me that the system is “thinking” that there's more pressure available than there really is, and it won't let the motor throttle up.

And if it only happens when it (whatever it is) gets hot, then the heat has to be affecting this throttle mechanism to prevent it's proper operation.

That's about what I can contribute. Sorry I couldn't be any help.

Any other visitors have any ideas for Cooper?

Bill

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Wiring a compressor pressure switch

by Jason
(Michigan)

I am trying to figure out how to wire the pressure switch on my electric stage 1 air compressor.

The guy I got it from had the cord off, now there is the cord with 3 wires, the cord from the motor with 3 wires and the pressure switch with 2 wires...????????????






Bill answers...

Hi Jason:

I'm sorry, I can't give wiring advice as I'm not an electrician.

Please visit the on-line source for your pressure switch, and ask them for a wiring diagram for the switch.

Or, if any reader can advise Jason, please chime in.

Bill

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Replacing the air pressure switch

by Bruce E Schmidt
(Davidson, NC)

We have to replace the air pressure switch on a single stage Farmhand air compressor 60 gal.

The pressure switch has 4 connections on it with plastic hoses and fittings that I haven't came across before, looks like you have to push on the fittings some how and helped would be appreciated.

Bruce
______________
Bill answers...

Hello there Bruce.

Is the question how to use an "instant fitting"?

If so, here's a "heads up".

An "instant fitting" is a remarkable device for quickly installing and removing air line.

It works this way.

Inside the tube port of the fitting (usually there is one side threaded, and the other side has a hole into which you push the tube) is a metal (usually stainless steel) collet that compresses out of the way as the tube is slid in and by it.

There's also an "O" ring through which the tube slides to pass through the collet.

The collet has "fingers" that point into the fitting.

As the tube passes by them, they are depressed (no not sad, just pushed out of the way) by the tube.

When you try to pull the tube back out, the collet fingers actually pierce the surface of the tube a little, preventing easy removal of the tube.

When there's air pressure in the tube, it expands somewhat. That makes the tube bigger, and makes the fingers on the collet "grab" the tube even harder, making it almost impossible for the tube to leave the fitting while it's under pressure.

There will be a slide ring or pressure ring on the outside of the fitting near where the tube is inserted.

By pushing this ring towards the fitting you will depress further the fingers on the collet, allowing them to move away from the surface of the tube, and theoretically allowing the tube to be removed from the fitting.

No, don't do this while the tube is under pressure.

Yes, void the pressure from the tube before trying to remove it.

Will removing it be simple? Nope. Over time, the fingers on the collet will stick into the tube, and even aggressively pushing on the slide ring may not dislodge the fingers.

After a while, you may curse the whole concept of "instant fittings", yet some are better than others, and actually work, even if installed on a charged air tube for some time.

If you go to this page, look at the blue ring on the in-port of the fitting. That's the slide or tubing release ring.

Does this help, or have I answered the wrong question?

Cheers,

Bill

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Changing pressure switch value.

by John Hill
(Napa Valley, CA)


I want to run two compressors in series. One has a high pressure cut off of 100lbs. and the other 145. I need to lower the 145 to 100 so the pressure relief valve in the smaller compressor doesn't blow.

I need the combined storage 80gal. and CFM, about 16.5, to run my sandblaster without constantly having to stop to let the pressure come back up.

Is the pressure switch adjustable or if fixed how are they set at the factory?? Any info appreciated. It is a DeVilbiss 60 gal. oiless.






Bill answers...

Hi John. It's been a few years since my wife and I spent some time in your backyard, Napa Valley. Nice place in the world you live!

I'm not sure that your PRV would blow at 145 PSI, so if that's the only reason for changing the pressure switch settings, you may not have to. Only one way to find out...right? Test it.

I've uploaded a photo of the innards of the pressure switch on my compressor.

You can see (actually, you can't see 'cause they are covered in sealant) at this end there are two nuts. One adjusts the high pressure cut-out, the other the low-pressure cut-in.

They are often sealed, as mine are, so that the factory knows if you've been messing with the settings, should you ever need to take your unit in to the shop.

John, you'll have some plumbing issues to consider when joining two tanks together.

Cheers,

Bill



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Aug 14, 2009
Thanks.
by: John Hill

Thanks Bill.

_________________

Most welcome.

B.

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How do i adjust the turn on and turn off pressure of my air compressor?

by leaman
(seattle WA)

Bought the tank used. Tank rated for 120 p.s.i.
I think the prior owner of the compressor messed with the settings. There appears to be / are two adjusting screws.






Bill answers...

Hello Leaman, nice to hear from Seattle.

It sounds to me like you've already found the device that turns on your compressor at the cut-in pressure point, and shuts it off again when it reaches the cut-out pressure, and that device is the pressure switch.

Some are meant to be adjusted. Others are not.

You say the previous owner "messed with the settings" yet you don't indicate what the present settings are.

You are correct, if your pressure switch has two nuts on a threaded rod with springs below them, those are the adjusting nuts.

Make sure you pull the plug first.

Look inside the cover to see if there are any instructions printed there.

You should have noted also at what pressure point your compressor cuts-in and cuts-out now. Drain air from the compressor until the pressure setting is below the cut-in point.

Turn one of the nuts tighter (this should increase the setting) 1 turn. Plug the compressor back in, and see what the change has accomplished, and which setting changed. (The cut-in or cut-out level)

Mark on the pressure switch cover which nut is which, and continue adjusting to suit.

Beware that you do not set the cut-out pressure too high. You could have disastrous results.

Cheers,

Bill

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