Compressor Pressure Switch Is Leaking Air

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What has happened to it when your air compressor pressure switch is leaking air?

Essentially, there are two reasons why this can occur.

But first, lets talk about what the pressure switch does for the air compressor.

A pressure switch reacts to pressure. In the case of your air compressor, the pressure switch is typically plumbed so that the air from the compressor air tank can flow to the switch. It is the air in the compressor tank that the pressure switch is sensing.

General Air air compressor pressure switch

Compressed air pressure pushes equally in all directions at the same time. So, if the tank gauge reads 120 PSI, then there is 120 lbs of force pushing on each square in of tank area, and through the line up to the pressure switch, 120 lbs. of force is pushing on each square inch of the diaphragm inside the pressure switch.

It is the tank pressure pushing on the diaphragm inside the pressure switch that causes the pressure switch to trip.

Why a compressor pressure switch is leaking air – reason one

Reason one why your compressor pressure switch is leaking air is that, over time, the diaphragm inside the switch has cracked or worn a hole, and air is blowing from inside the tank, through the hole in the diaphragm, and existing the switch housing through any convenient opening.

In the photo above, the electric wire ports would be logical places for air to exit the cover should the pressure switch diaphragm have become holed. If the wire strain-relief fittings fill the apertures in the switch, then it may be necessary to pull the cover off the switch to investigate for leaks. If you do this, ensure that the compressor has been unplugged from any power source.

In this photo, note also that the unloader valve for this pressure switch is located on the outside of the switch. If air is exiting the pressure switch cover, then it is almost certain that the diaphragm has failed. That may not necessarily be the case if the

Resolution:

If, when the air compressor has reached cutout pressure and stopped, you notice that air is blowing out any openings in the pressure switch cover, or if you remove the cover and feel air escaping, and particularly if the unloader valve is plumbed outside of the switch, then you either disassemble the switch and replace the diaphragm, or you replace the switch with one of the same pressure and voltage rating as the old model.

Getting parts for pressure switches may be difficult. Disassembling them and reassembling them is, too, quite complex, particularly when you may only do it once or twice in a lifetime.

If it were us, we’d simply purchase a new switch and replace the old. In this manner the removal and re-installation is straightforward, you get a new diaphragm in the switch, and you also get new points, which are another wear item in a typical compressor pressure switch.

Why a compressor pressure switch is leaking air – reason two

If you notice that the pressure switch on your compressor is leaking air, locate the unloader valve, and try to determine if  the air is leaking from the unloader valve or from the switch itself.

If air is leaking from the unloader valve when the air compressor is stopped, that points to a problem with the compressor tank check valve not seating properly, or its failure.

Resolution:

If the air is leaking from the unloader valve, then see the page under Fixing Compressor Problems about air continuously leaking from the unloader valve for more information.

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Jason Zook
Jason Zook
June 19, 2020 9:21 pm

I have a Hitachi compressor. The small line that goes to the pressure switch is popped off of its connection at the tank. I do not know how to connect it. Looks like it should be a compression fitting. But there is only a bare line and a nut. Should there be more parts?

Jason Zook
Jason Zook
Reply to  Jason Zook
June 20, 2020 12:15 pm

Its a plastic 1/4″ line at the bottom tank connection, should show in the photo

Jason Zook
Jason Zook
Reply to  Jason Zook
June 21, 2020 6:42 pm

I can’t get the pictures to load.
My hardware guy gave me a connector; pipe thread to compression coupler and it fixed my line, thanks!

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Jason Zook
June 21, 2020 12:54 pm

Sorry, no photos arrived.

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Jason Zook
June 20, 2020 10:43 am

Please add a comment to this thread, click the “paper clip” icon, and upload some photos of the compressor and the problem area in question. Thanks.

Dozier James
Dozier James
June 17, 2020 1:10 pm

I replaced a new pressure switch, exactly like this one. It shuts off and on fine but there is air continuously leaking through the little hole of that “swivel valve” (I think that is what it’s called). I used the original nut/coupler to attach the tubing to this part. (I couldn’t slide the nut off without possibility damaging the tubing). Is there something wrong with the connection or the part. Thanks so much for any feed back.

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Dozier James
June 17, 2020 2:25 pm

I do not see a photo of the pressure switch. Please add a comment with a few photos, in particular, a closer image of where the air is leaking. Thanks.

Dozier James
Dozier James
Reply to  Fix My Compressor Moderator
June 18, 2020 12:38 pm

Thanks for answering. I thought I attached pictures initially, but apparently didn’t. Sorry. Here are two pictures. The first pic is the swiveling valve. Which is what I was talking about. I spent some more time trying to figure out the problem. Apparently, there is a small pin that sticks out of the opening of that valve. When the pressure builds up the pin pushes outward. The little pin butts up to an actuator arm. Such that when the arm pushes the pin inwards it causes air to leak thru the valve. Or vice versa, I guess.

Anyway, I found that, even at maximum pressure, when the motor stops, the actuator arm doesn’t allow the pin to go to the full out position.

Therefore, there is a small air leak. I tried some WD40, which really didn’t help. Not sure what to do, if there is anything that could be done. It seems like it’s sort of a design flaw and/or the tolerances aren’t very good.

It took me 10 weeks to get this replacement part and a bunch of hassle. (PartsWarehouse.com, don’t recommend). So I won’t be sending it back. If you do have any suggestions that would be great, but I understand if you don’t. Thanks again James.

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Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Dozier James
June 18, 2020 5:25 pm

Thanks for the pics. The first pic is of the fitting where the air is leaking out from a hole in the top. It’s not coming from the tank plug, but out of the part that has the line from the pump plumbed to it as per your description.

I surmise that somewhere in there is a flapper valve to keep air in the tank when the pump stops pumping and the unloader valve opens. Is there? If so, I think the issue may be that the flapper (or also known as check valve) may be leaking.

fathi
fathi
March 23, 2020 8:14 am

thank you for your advise.it is was helpful. .

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  fathi
March 23, 2020 10:59 am

Glad to hear it, Fathi.

Ronny Ursuery
Ronny Ursuery
September 9, 2019 8:52 pm

I need a schematic or diagram on how to reassemble.a pressure valve for Campbell and Hauser. Compressor

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Ronny Ursuery
September 9, 2019 9:47 pm

Ronny, I take it you mean a Campbell Hausfeld air compressor, and the pressure valve you speak of is the pressure switch? While it is possible to reassemble a pressure switch, I’d not do it personally. Rather, I’d get a new one. However, if you want some guidance from another visitor on how to do this, you’ll need to identify the model and year of compressor in a comment here, as not all of their compressors have exactly the same switch. Good luck.

Thomas Bardwell
Thomas Bardwell
June 13, 2017 11:32 am

I have a 60 gallon air compressor belt drive,here is what it’s doing.. no start,new start capactor,new run capactor.. windings ok..voltage at motor,and switch… Has no ark when switch engaged…is the diaphragm bad in switch?

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Thomas Bardwell
June 15, 2017 8:05 am

“Motor at voltage and switch” So, you’ve used a meter and see that power gets to the pressure switch, and with the tank empty, power is flowing across the pressure switch to the motor side, Thomas? “Has no arc when switch engaged” means what? You’ve watched the points connect inside the pressure switch, and you cannot see a spark? Doesn’t mean that the connection isn’t working. If, when the tank is empty, you’ve got power on the motor side, then the switch would appear to work. What makes you suspect that the diaphragm is bad then? What’s the make and model of the compressor?

Chris Selander
Chris Selander
May 1, 2017 4:59 pm

I have an older craftsman air compressor which is a 5 1/2 horsepower 26 gallon tank and the presume switch has gone bad. Can you steer me in a direction for a replacement part, the numbers are all worn off so I don’t have any model numbers. Thank you

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Chris Selander
May 1, 2017 10:54 pm

I presume you mean the pressure switch, Chris? If so, please take a photo of the existing switch and post in here. Since you don’t have a compressor model number, there is no way I can be certain what switch you have without seeing it.

Victor Heddins
Victor Heddins
August 2, 2015 7:00 am

Thanks for the Good article.

I have a electric air compressor that wasn’t used for about 7 years, and when I got it, it leaked. So I took all the connections off on the entire machine. I cleaned them with a wire brush and put them back together with pipe tape. And it began to leak even faster to the tune of a 5 gallon tank gone in about 2 hours.

You may be on to something here. Question, whats the best method for spotting an air leak? and 2nd what’s the best place to buy these parts such as a pressure switch?

Thanks
………………….

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Victor Heddins
August 2, 2015 10:49 am

Your first culprit may be the tank check valve, Victor. So do check that and make sure that it doesn’t leak. As to parts for your compressor, if you Google your compressor make and model number, you may find sources. We appreciate your kind words.

Louis
Louis
May 20, 2015 9:11 am

I replaced the pressure switch on my air compressor and the new switch leaked. I return that switch and got another new one and this one is leaking too. I know it is not the unloading valve due to it is not located at the switch. Do you have any suggestions. could two new switch be bad?

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Louis
May 20, 2015 11:17 am

Different pressure switches have different unloader valve configurations. If your new switch has an internal unloader valve, and air is bleeding out of the switch even when the compressor is off, that points to a leaking check valve for us, not a problem with the pressure switch. When you say that “I know it is not the unloading valve due to it is not located at the switch”, if the leak is not at the pressure switch, why are you changing it? We’re obviously missing something here. Maybe you could add a comment here with more details, and, if you want, upload a photo of where the compressor is leaking, along with what is it’s make and model number?

Louis
Louis
Reply to  Fix My Compressor Moderator
May 22, 2015 2:10 pm

It is leaking at the pressure switch and this is the second new switch I have tried. Attached it a picture of where the new switch is leaking. It is an old Craftsman 6hp 60 gallon single stage.

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Louis
May 22, 2015 2:19 pm

Hey Louis. If the pressure switch is leaking, and it’s the second pressure switch you’ve tried on your old Craftsman air compressor, then it’s not likely the switch that’s the problem. Our suggestion is that you want to have a look at your tank check valve, and if you see that page on this site, you’ll have a better understanding how the tank check valve, and your pressure switch unloader valve work together. Simply put, we’d bet you’ve got a leaky tank check valve. Hope this helps, the boys at Fix-My-Compressor.com.

Louis
Louis
Reply to  Fix My Compressor Moderator
May 22, 2015 2:26 pm

Thank you for you help I will try that this weekend and let you know how it goes.