Compressor is always leaking air

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You know the compressor is always leaking air as when you shut it down with a full charge of air in the tank, after a short while you can see that the tank pressure gauge display is showing that the tank pressure is dropping. Soon, if the air compressor is plugged in, the pressure switch will react to the falling tank pressure, and start the compressor.

That’s a waste of energy and money, for sure.

The first thing to do is to determine where the leak on the air compressor is. Here are some tips on that.

No obvious leaks

If you can’t hear the leak, or feel it with your fingers, you can soap the connections on the air compressor.

First pull the air hose from the coupler on the compressor.

Use a tablespoon of liquid dish soap to a cup of luke-warm water. Brush this solution onto all the connections on the compressor, including into the end of the coupler.

Coupler opening - www.fix-my-compressor.com
Make sure you check up in here with the soapy water. Couplers have been known to leak.

If there is an air leak, bubbles will form where compressed air is escaping.

If you find a leak this way, tighten the fitting, and test again. Make sure there are no more leaks on the connections on the air compressor.

Check external unloader valve for leaks

If your air compressor has a pressure switch with an external unloader valve, make sure you soap it thoroughly as well.

Compressor pressure switch unloader valve - www.fix-my-compressor.com
If soaping the pressure switch external unloader valve – one of which is seen in this image – make sure your compressor is unplugged with lots of air in the tank. With the compressor off, the unloader valve should NOT be leaking any air at all after the unloading process, a second or two, has completed.

If you find that your compressor pressure switch unloader valve is leaking air continuously, then you have located at least one of the leaks on your air compressor.

A pressure switch unloader valve that leaks continuously after the compressor has stopped indicates that the tank check valve has not closed completely, and compressed air is no longer trapped in the tank.

You will need to dump all the air in the tank, and with the compressor unplugged, disconnect the air line from the pump, remove the tank check valve, inspect it, clean it, or replace it, depending on its condition.

More information on tank check valves is available on this site. See the link Tank Check Valve under the Compressor Information list in the right column.

Does compressor only leak air with a hose plugged in?

If the compressor is only dropping when there is an air line plugged into the coupler, then the leak will be found downstream from the compressor coupler.

To confirm this, unplug the air line. If the air leak stops, the hose has a hole, or a connection downstream of the compressor coupler is the problem.

Still have a compressor air leak?

If you still cannot find the compressed air leak, add a comment below and we’ll see if we can help.

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Nick
Nick
March 25, 2022 8:40 pm

I have a Craftsman 3HP, 30Gal compressor model # 919.17633. I’ve replaced the drain valve and moved it to a more accessible area. I’ve replaced both gauges and the tank check valve and soaped every connection on the tank and compressor and it’s still losing air.

art
art
March 25, 2022 11:53 am

i have a kaesar m26 i put a rebuild kit in the vent valve and when i start the engine it still leaks out the vent valve do i need to replace valve. valve thank you art from tools unlimited

Gary Smith
Gary Smith
May 15, 2021 2:11 am

I have a small belt-driven compressor (1,5HP) and its started leaking air around the tank drain plug. Rust is the problem I think, as I didn’t drain the tank properly after each use!! Can the tank be repaired? It is possible to drill out the existing drain plug and fit a bigger new one in its place? Hope someone can help?

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Gary Smith
May 15, 2021 12:24 pm

If there is visible rust around the drain plug, there is likely rust all along the bottom of the tank, Gary. It’s my view that a compressor tank that’s compromised by corrosion should not be fixed as it will, thereafter, be a candidate for tank rupture under pressure. Other opinions vary, however.

I also think that doing a proper repair job on the tank may cost as much as or even more than a replacement tank or a replacement compressor of the same size, assuming the use of a qualified welder.

I advise against attempting a repair on a tank that’s clearly compromised.

Burak(Bu-rock)
Burak(Bu-rock)
February 10, 2021 4:58 pm

First of all thanks for this great website.
I made myself a compressor. At some point I got stuck and I’m about to cry: D. I need a very simple compressor. To blow the powders. I marked the check valve in the image. The copper pipe coming out of the check valve goes under the pressure switch. I also marked it in the image. The moment I start the compressor, all the air comes out of there. It does not enter the tank. I just bought and replaced the check valve and pressure switch, but the problem still exists.

IMG_8962.jpg
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IMG_8978.jpg
Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Burak(Bu-rock)
February 11, 2021 8:16 am

First step, empty the air, pull the check valve, and make sure that it’s only flowing air into the tank and not back out again. Please advise.

Burak(Bu-rock)
Burak(Bu-rock)
Reply to  Fix My Compressor Moderator
February 11, 2021 12:38 pm

Thanks for the reply. The system I set up did not work properly even once., I have never been able to fill the tank. As you said, I pulled the check valve. air is entering the tank and Not coming back. I played with a plastic object(wd40 plastic pipe) where I showed in the 3rd image and something happened. I could not understand. Worked as it should. I wonder if the two pressure switches I bought are also broken?

Last edited 1 year ago by Burak(Bu-rock)
Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Burak(Bu-rock)
February 11, 2021 4:25 pm

It’s possible they are both faulty… but that’s a reach. What’s the make?

Also, most of the pressure switches I see with an integral unloader valve don’t have a threaded port, but rather, have a quick connect port into which a 6mm or 1/4″ unloader tube is connected.

How did the threads get there?

Bu-rock
Bu-rock
Reply to  Fix My Compressor Moderator
February 13, 2021 9:51 am

The third pressure switch arrived today and the same problem continues. I started to suspect everything. I removed check valves from the system and checked their springs. No problem.(two check valve that i have). Can you confirm that my check valve connection is okay ? inlet and outlet way is correct ?

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Bu-rock
February 13, 2021 10:38 am

Doggone. Did you check this… “most of the pressure switches I see with an integral unloader valve don’t have a threaded port, but rather, have a quick connect port into which a 6mm or 1/4″ unloader tube is connected. How did the threads get there?” What is the make and model of the pressure switch, please?

It is possible that the check valve, while working, is installed with the tank fitting is where the check valve input is plumbed. As an experiment, reverse the installation of the check valve. The tube to the pressure switch stays where it is.

Burak(Bu-rock)
Burak(Bu-rock)
Reply to  Fix My Compressor Moderator
February 13, 2021 10:58 am

yes I checked what you said. Pressure switch is the same product on this link.
link
When I use it with another check valve, it gives the same result. Problem still exist.

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Burak(Bu-rock)
February 13, 2021 11:59 am

OK, that switch has a compression fitting on the bottom, so the tube inserts all the way (about 1/2-3/4″ or so) and then the nut is turned clockwise until the internal compression ring seals tight on the tube. If the compression ring hasn’t sealed air could leak out, but only when the compressor is running.

The bottom line is, if air is leaking from that fitting when the compressor is off, the only place that air can be coming from is the tank, and that means that the tank check valve is not blocking air from getting into the unloader tube. There is no other source for air to flow out of the pressure switch, IF THE COMPRESSOR IS OFF! Is air leaking with the compressor off?

Burak(Bu-rock)
Burak(Bu-rock)
Reply to  Fix My Compressor Moderator
February 13, 2021 12:23 pm

I’ve only been able to fill the tank once. I was able to achieve it while playing with a plastic pipe (wd-40 red plastic pipe) with the place in the 3rd image. I pulled the plastic pipe and the air started to fill into the tank without evacuating from there and stopped when it reached 8 bar. In all my attempts other than that, there is no air leak when I turn off the compressor because no air enters the tank. I open the switch, the air pumped by the motor goes out through the unloader valve.I understand from this that there is no air leak when the compressor is off. English is not my native language, I can make a video if you want. I am grateful for your time.

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Burak(Bu-rock)
February 13, 2021 1:52 pm

In looking more closely at the pressure switch / unloader line connection, I’m seeing a hole in the side of the connector through which I can see threads. That seems odd to me.

Regardless, can you pull the line to the check valve from the pressure switch and plug the inlet in the switch somehow? I am trying to see if air will go into the tank if the unloader valve is completely out of the circuit.

Bu-rock
Bu-rock
Reply to  Fix My Compressor Moderator
February 13, 2021 2:41 pm

I did it the way you said, I pressed it with my finger. and filled 4 bars. I stopped the compressor now. 5 minutes have passed. There is no leak.

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Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Bu-rock
February 13, 2021 4:12 pm

OK, a couple of things. Do not use plumbing sched 40 or sched 80 to plumb compressed air… ever! It isn’t rated for the pressure fluctuations.

The other, I think that how you’re connecting the unloader tube to the pressure switch is leaving an opening through which the compressed air can flow as pressure is trying to build in the tank. Make sure that the fitting-to-pressure switch is air tight.

Burak(Bu-rock)
Burak(Bu-rock)
Reply to  Fix My Compressor Moderator
February 13, 2021 4:31 pm

Yes, I understand that I will try to change the copper pipe and fitting and I will definitely write the positive and negative results to you. But first one i dont sure i understand you correctly. What am i using and what is wrong with it ? is this about my black pipe ?
I bought the hose I used as Rubber braided and it says that it is safe up to 30 bar/435 psi. There is no problem, right ?

Last edited 1 year ago by Burak(Bu-rock)
Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Burak(Bu-rock)
February 14, 2021 3:58 pm

Burak, you’ve pulled the copper tube from the check valve, and when the compressor runs, air builds in the tank. It doesn’t escape out the check valve, proving that the check valve is not leaking.

Burak, there should not be air coming from the pressure switch unless the compressor is off, and then only long enough to drain the copper unloader tube. If air is coming out of the pressure switch when the compressor is running, either the unloader valve inside your pressure switch has failed or the diaphragm in the pressure switch is allowing tank air up through the switch and out to the atmosphere.

You say, “What am i using and what is wrong with it ? is this about my black pipe ?” What does this question mean?

You then said “I bought the hose I used as Rubber braided and it says that it is safe up to 30 bar/435 psi. There is no problem, right ?” I understood that you were using sched 40 plastic pipe from an earlier comment, and that’s not good. The hose you refer to later should be fine.

Burak
Burak
Reply to  Fix My Compressor Moderator
February 15, 2021 3:07 am

Oh, I guess I annoyed you a little bit, I’m trying to be precautious for trying not to make a mistake. And since I am not a native English speaker, I may have seemed rude when I expressed myself in writing, I am grateful to you. I ordered a better quality switch, not a non-branded product made in China. I will make a new copper pipe and fittings and try again.

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Burak
February 15, 2021 8:42 am

Nope, not annoyed. Just trying to understand. If the check valve is holding air in the tank, and the air is coming out of the pressure switch when the compressor is running, it pretty much has to be the switch that’s the problem. Good luck.

Burak
Burak
Reply to  Fix My Compressor Moderator
February 19, 2021 5:29 am

Hello ,me, again. A local manufacturer is producing pressure switches, I found it when I researched it. And it was a quality product that could not be compared with Chinese made and non-branded products. A modular product that can be separated the unloader valve from the switch. I connected it to the compressor and my problem was solved directly. You have helped me a lot with your experience and knowledge, I am grateful to you.

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Burak
February 19, 2021 8:35 am

Glad to be of what little help we were. Good luck.

Thug
Thug
October 28, 2020 11:10 pm

I just bought a brand new Quincy 60 gallon compressor from northern tool. When it came I did the required 1 hr break in with the air valves open so it doesn’t have to compress the air. After the break in was complete I fired it up and filled the tank. Filled nice and quietly. After it kicked off I noticed the gauge dropping. So I got my soapy water and started checking all the connections. I found one small leak on the tank drain. Fixed it. Problem persists. I have checked every fitting 10 times now. No luck in locating a leak. I do air pressure tests all the time at work so I know what to look for. Looking forward to your feedback.
Thanks

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Thug
October 29, 2020 10:01 am

If the compressor fills and stops and you note a continuous drop in air pressure, in the absence of any leaks, two things come to mind, Thug. Did you check the discharge coupler? Insert a connector, remove it, then soap test the coupler.

The other, and more likely cause is a tank check valve leak. Air leaking by there will vent out of the pressure switch and may not be noticeable.

If it’s not the coupler, dump all air with the compressor off, pull and check the tank check valve.

Did that get it?

Johnny W Jones
Johnny W Jones
July 26, 2020 8:27 pm

Kobalt model 99007-A My compressor is several years old and works well except for an air leak where the pressure switch mates to the regulator. I was able to obtain and replace the “O” ring but this did not solve the problem. I would appreciate any suggestions to stop the leak. The leak makes an annoying constant high pitch squeal. I can feel the air coming from between the switch and regulator. Thanks!

Last edited 1 year ago by Johnny W Jones
Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Johnny W Jones
July 27, 2020 9:41 am

The compressor has a tank check valve “3/8″ Comp X 1/2″ MPT with 1/8″ FPT side port.” I suspect that yours is leaking. Remove, clean, check and if still leaking, replace it.

Johnny W Jones
Johnny W Jones
Reply to  Fix My Compressor Moderator
July 27, 2020 10:03 am

The pressure switch has a round protrusion which slides into a corresponding flat bottom, round depression in the regulator/manifold that has a rubber “O” ring. This is where the leak occurs. No other valves, fittings, etc have a leak. A new “O” ring did not help at all.
I attempted to include diagram showing area including switch and regulator but it did not work.

Last edited 1 year ago by Johnny W Jones
Johnny W Jones
Johnny W Jones
Reply to  Johnny W Jones
July 27, 2020 12:05 pm

I get message .jpg file type not supported. What image type does system accept?

Johnny W Jones
Johnny W Jones
Reply to  Johnny W Jones
July 27, 2020 3:16 pm

The leak occurs where the black switch attaches to the cast aluminum regulator/manifold. The white plastic hex is the OFF/AUTO selector for switch. I have another photo (jpeg) showing the switch and regulator apart but again when I try to attach I get message file not supported.

SwitchRegTogather.jpg
Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Johnny W Jones
July 29, 2020 8:23 pm

Thanks for the .pdf. Don’t know why you are having such issues uploading. I’ve tested and uploaded up to a 5 MB file with no issues. Anyway, sorry about that.

All I can surmise from the issue outlined is that there might be a diaphragm leak, but no, I cannot be specific and I am not sure.

Johnny W Jones
Johnny W Jones
Reply to  Fix My Compressor Moderator
July 30, 2020 9:21 am

Upload problems I suspect are caused by some quirk in my system/browser. I appreciate your patience with my difficulties. The leak causes other problems in addition to annoying noise. Compressor takes about 25 plus minutes to reach 150 and shut off then drops pressure so compressor cycles on and off. I’ve considered using J-B Weld to permanently bond/seal switch to manifold. This would be disastrous should I block air passage from/to switch so I’m hesitant to do this.  Thanks again for your willingness to help!

Johnny W Jones
Johnny W Jones
Reply to  Johnny W Jones
July 29, 2020 11:47 am

Received email stating ‘comment was approved’ but comment still has ‘Awaiting for approval’. I’m hoping you were able to view PDF make suggestion how to stop leak.. I made several more attempts to save other .jpg’s without success. I reduced to small size (54KB), and saved in couple different formats still without success.
Thanks!

Johnny W Jones
Johnny W Jones
Reply to  Johnny W Jones
July 27, 2020 5:58 pm

PDF has both photos. Leak in area circled in blue. Small white circle was there from manufacture. Leak occurs while compressor running and while off, and continues until tank is empty. The “O” ring goes between switch and regulator on the round protrusion. I’ve tried placing “O” ring on/around protrusion and on the flat inside depression or hole protrusion fits into. Doesn’t make any difference leak is same both ways.

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Johnny W Jones
July 27, 2020 5:15 pm

I cannot account for why you cannot upload a .jpg or .jpeg files. Sorry. I’ve just uploaded the following .jpg file with no issues.

The black switch is the pressure switch, yes? The leak is the area you have circled?

compressor leak point

That being the case, though it looks like a flaw, it must be on purpose, and that purpose, I believe, is to vent air from over the compressor piston. If I’m right, this will leak while the compressor is running, and it will still leak when the compressor stops… right? If so, if the compressor is off, where is the leaking air coming from? Please advise.

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Johnny W Jones
July 27, 2020 1:44 pm

I have gone into the files and updated them all. Please try again. Thanks.

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Johnny W Jones
July 27, 2020 11:22 am

Please add a comment with a photo of the area in question. Thanks.

Frank
Frank
July 24, 2020 8:37 pm

I have a 60 gallon tank. I filled it to 104 pounds. In 19 hours it dropped to 101. Is this normal? If it worth trying to trace down?

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Frank
July 25, 2020 11:21 am

It sounds like a pinhole leak and not something I would worry about, Frank. That is, unless it’s an old tank, and a pin hole leak in a tank often means there’s significant rust on the inside and the pin hole is a center of a weak spot. That needs attention. Otherwise, this compressor being mine, I wouldn’t even worry about.

Joe
Joe
June 27, 2020 7:26 am

line from Air copressureis capped off and it is still loosing air

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Joe
June 27, 2020 8:03 am

Not a lot of info, Joe. What line from the compressor is capped off? What make and model of compressor? Please provide additional info and a photo of the compressor in your answer. Thanks.

adam
adam
January 19, 2020 7:16 pm

I bought a brand new kobalt 60 gallon two stage compressor. I added a ball valve to the side of the tank and removed the original mickey mouse drain valve and replaced with a street elbow with ball valve. Wanted to test for leaks first so I turned it on and let the compressor pressurize to 174 psi and noticed the plug at the rear of the pressure switch and the pipe nipple from the tank to the pressure switch were BOTH leaking. I resealed both of these and decided to reseal the unloader valve fittings at both the pressure switch and at the compressor pump discharge fitting connection at the check valve. All connections and fittings were sealed with teflon tape with a coating of pipe dope on top of the teflon tape.

Ran the compressor again to 174 psi and the pressure has now dropped down to 117 psi in 24 hours. The temperature did drop from 34 degrees down to 21 degrees in this time period so I’m guessing some of this pressure loss is due to the change in temperature. Did a soap test at all fittings and everything has checked out. Should I take the compressor back?

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  adam
January 20, 2020 5:12 pm

If new, yup, I’d take it back. You might have an absolute lemon, or you might just have a leaking tank check valve, but regardless, it shouldn’t be doing this when new.

Mitchell Nelson
Mitchell Nelson
November 20, 2019 2:33 am

New gauge, 3 new check valves ,pressure switch and safety valve tank soaped all around welds repair guy can’t find leak.Brand new 60 gal 5 no NorthStar compressor.Don’t know what to check

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Mitchell Nelson
November 20, 2019 8:46 am

Did they check the regulator vent hole, and the tank drain valve, please?

Mitchell Nelson
Mitchell Nelson
Reply to  Fix My Compressor Moderator
November 20, 2019 9:42 am

yes he soaped down everything

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Mitchell Nelson
November 20, 2019 11:01 am

Man, that’s got to be driving you nuts.

If the compressor is off, and the tank is full, and there’s an air leak, and you’ve ruled out the tank check valve, the unloader valve, the tank drain, the discharge coupler to the air line from the tank, then really, it’s got to be the tank itself. It cannot be anything else. I don’t know how fast the air leaks out, but a pin-hole leak might be the issue?

Mitchell Nelson
Mitchell Nelson
Reply to  Fix My Compressor Moderator
November 23, 2019 12:45 am

But if it is a pin hole all the air would leak out right?

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Mitchell Nelson
November 23, 2019 8:58 am

Yes, but only until the cut in pressure in the tank was reached, and then the compressor would start again.

If the air is leaking out of the tank after the compressor stops, it can only be 1) leaking tank check valve 2) leaking tank drain valve 3)leaking discharge coupler 4) pin hole in tank. There is no where else the air could be getting out of the tank.

Mitchell Nelson
Mitchell Nelson
Reply to  Fix My Compressor Moderator
November 23, 2019 10:45 am

Check valve have been changed 3 times and everything soaped tank is holding at 128 psi now been holding for 2 days. Just leaks from135 psi

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Mitchell Nelson
November 23, 2019 1:46 pm

So, at 128 PSI no leaks, at 135 PSI it leaks. That certainly suggests that the little bit higher pressure is opening up something to the atmosphere. Of course, you did the soap test at 135 PSI, yes?

Howie
Howie
November 5, 2019 8:52 am

I have a Husky upright compressor from the Orange Big box. Since new it has leaked from the safety valve right down to 0 psi within a few hours. I have replaced the valve with one of the same pressure rating and it still leaks. The leak is not at the threads but out of the end as if it is partially open. I have removed and tested the tank check valve which seals properly. I’m not sure what else to try, any ideas?

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Howie
November 5, 2019 9:25 am

Howie, by safety valve you refer to the pressure relief valve, right? Is this leak occurring after the compressor fills and stops?

Howie
Howie
Reply to  Fix My Compressor Moderator
November 6, 2019 7:24 am

Yes, Exactly, it fills and stops normally and the relief valve hisses right away. I filled it yesterday and it went from 120psi down to about 40 in about 3 hours

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Howie
November 6, 2019 9:48 am

If air is leaking anywhere on the compressor after the compressor fills and stops, that air has to be coming from the tank, and that always points first to a leaking tank check valve. Remove and clean yours, after all air is dumped of course, and then reinstall and see what’s what. Let us know, please, Howie.

Mitchell Nelson
Mitchell Nelson
October 24, 2019 11:29 am

Northstar 60 gal less than a month old never gets to 135 psi and when it shuts off leaks down to 120 psi. Soaped down everything and replaced the check valve and safety relief valve and still leaks down

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Mitchell Nelson
October 24, 2019 10:02 pm

No visible leaks when you soaped everything? No tank leaks out the tank drain valve? Did you soap the unloader valve too?

Mitchell Nelson
Mitchell Nelson
Reply to  Fix My Compressor Moderator
October 24, 2019 10:54 pm

yes and Northstar sent new gauge also

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Mitchell Nelson
October 25, 2019 8:04 am

How fast does the tank pressure drop to the cut in pressure setting?

Mitchell Nelson
Mitchell Nelson
Reply to  Fix My Compressor Moderator
October 25, 2019 9:44 am

After compressor shuts off reaching 130 psi and never gets to 135 psi about 10 min to leak down to 120 psi and hold.

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Mitchell Nelson
October 25, 2019 10:09 am

Are you saying that the normal “cut off” is 135 PSI, but the compressor never gets to that pressure, but shuts off automatically at 130 PSI? If so, that’s not unusual as pressure gauges may be off by the much in displaying system pressure. If, however, you are shutting the compressor off, that suggests a different scenario. Which is it, please?

Mitchell Nelson
Mitchell Nelson
Reply to  Fix My Compressor Moderator
October 25, 2019 2:41 pm

Northstar say this compressor should shut off at 135 psi automatically but it shuts off at 130psi.Then it leaks down to 120 and hold there.It never gets to 135 psi

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Mitchell Nelson
October 26, 2019 6:37 pm

As noted in my earlier response, the difference between the 135 PSI shut off and the 130 actual shut off may only be a poor quality gauges giving the wrong reading.

As to draining down to 120 and hold there, that may be a small leak in the seal in the tank check valve that allows air to bleed by until the 120 PSI level, at which point it can hold that pressure in the tank. Drain down the system, remove and clean the tank check valve by rinsing in a solvent or paint thinner, let it dry, reinstall and test. If it still leaks down, you might consider replacing it.

Mitchell Nelson
Mitchell Nelson
Reply to  Fix My Compressor Moderator
October 26, 2019 10:05 pm

Check valve,safety valve and air line from check valve to unloaded valve have all been replaced.same. Problem

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Mitchell Nelson
October 27, 2019 11:51 am

I understand that this is frustrating. However, please consider this. When the compressor is off, the tank is full of air, and over time it bleeds down 20 PSI. If on the compressor the only place compressed air is the tank, then it HAS to be a leak from the tank, yes? Where are the typical places air leaks from the tank? 1) The tank check valve is leaking a little (in your case) and air is wicking past it back up and out the unloader. 2) You have a leak at the tank drain. Possible, but unlikely, as one would think all the air would leak out, not just 20 PSI. However, double check that by soaping the tank drain if you would. 3) Discharge coupler, air line fittings, connector to air tool, any or all of these could be leaking air. However, I consider this unlikely too, all the air would leak out, not just the 20 PSI.

So, that all points back to the tank check valve UNLESS there is a leak in the tank itself, and again, unlikely, as all the air would leak out I would think.

Neil
Neil
June 30, 2019 8:03 pm

I’ve identified the issue, its the black gasket between the shutoff valve and the tank. The problem is I can’t figure out how to order a new one. I took the 4 tiny nuts off and could see a crack in the black rubber gasket so pretty sure that’s the issue. How does one order just the gasket?

Central Pneumatic 21 Gallon Cast Iron Vertical Air Compressor. Heavy Duty 3HP Rated Motor. Model 47065. Its part 10B on page 10 of the Operators Manual

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Neil
July 1, 2019 9:46 am

Please add a photo as a comment showing where this gasket is located if you would.

Neil
Neil
Reply to  Fix My Compressor Moderator
July 1, 2019 12:09 pm

Image of the gasket is attached. It seems a few other people have had the same issue… but they didn’t say how or where to get the gasket.

gasket.jpg
Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Neil
July 1, 2019 2:55 pm

Neil, that looks like a regulator gasket. Is that where you removed it from? I have seen photos of the 47065, but no close ups of the plumbing for the discharge line which also includes the regulator, and that’s why I asked for a closeup of where the gasket was located.

If it is the regulator gasket, and you can remove just the regulator from the manifold, new regulators are around $15.00 including the gasket. Or, you can try, as some folks have done, using the old for a guide and cut a new one from a flat rubber sheet if you can find one in this day and age of tubeless tire.

Neil
Neil
Reply to  Fix My Compressor Moderator
July 1, 2019 4:13 pm

I’ve attached 2 pics. the gasket sits on top of the opening to the tank and below the pressure regulator that turns the pump on/off.

So there is no way to order just the gasket?

img1.jpg
img2.jpg
Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Neil
July 1, 2019 5:57 pm

Thanks for the pix. It looks the like the first pic is showing manifold base of the pressure switch. Is the brass “fitting” to the left of the base the pressure switch unloader valve?

If so, is there a part number or manufacturer’s name on the pressure switch itself?

Fix My Compressor Moderator
Fix My Compressor Moderator
June 20, 2019 12:53 pm

What is the make and model compressor please, and please upload a photo or two of the problem area. Thanks.

Gregg Rhode
Gregg Rhode
March 31, 2017 5:23 pm

I have a Devilbiss 6.5hp 80 gallon compressor that leaks at the manifold. My questions is what would I use to seal the manifold when I remove and replace.

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Gregg Rhode
April 1, 2017 3:17 pm

Are you speaking of what kind of air fitting thread sealant to use? If so, I prefer to use pipe dope versus the plumbers tape as a sealant. Regardless of what you use, as long as it is applied with care, any should suit.

John B
John B
February 12, 2017 7:40 pm

Hello
I just bought a Porter Cable pxcm201 and when it shuts off at 135lbs it leaks 5lbs of air within 30 – 40 sec and stops. It stays at 130 overnight. Do all compressors leak a few lbs? Should this be staying at 135 overnight? I soaped all the connection and can’t find a leak. It’s brand new and I want to find out where it is so I know if I should fix it or return it.
Thanks

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  John B
February 12, 2017 9:34 pm

All compressors with an unloader valve will leak when the compressor reaches cut out and stops. That leaking air is voiding pressure over the pump piston to allow an easier restart. Typically that venting takes place in a second or two at most. Odd that yours vents for 30-40 seconds, though since it only loses 5 PSI over that quite a long amount of time, that venting is fairly slow. I’m guessing first a sluggish tank check valve, and if not that, then a sluggish unloader valve could be the culprit.

John B
John B
Reply to  Fix My Compressor Moderator
February 14, 2017 8:59 pm

Also, I just did another soap test. I started the compressor and put soap bubbles all around and over the hole of the unloader valve immediately after it unloaded, watched it like a hawk and the bubbles didn’t budge. I don’t understand why I cant find any leaks anywhere unless the soap test isn’t fool proof. Sorry for the replies but it’s brand new and driving me nuts

Thank you

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  John B
February 16, 2017 11:40 am

That it stops after 5 PSI makes me wonder if it’s the gauge itself that’s leaking?

John B
John B
Reply to  Fix My Compressor Moderator
February 16, 2017 11:12 pm

Wow I didn’t think of that. This weekend I plan on checking/cleaning the tank valve and if it’s ok I’ll move on to the gauges. Thanks for all your help

John B
John B
Reply to  Fix My Compressor Moderator
February 13, 2017 5:33 pm

Thank you. I should have been more clear about it. Yes it releases air when it reaches cut out pressure and all is quiet, then if looking at the gauge it slowly drops 5lbs. Would you return it or fix it?

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  John B
February 16, 2017 11:39 am

John, difficult to be sure. Without pinpointing the leak. If you can take it back for a replacement, I suspect that’s what I would do.

mark
mark
December 25, 2016 2:41 pm

I have a slow pressure leak in my 30 gallon, 150 PSI vertical compressor, but it stops leaking when it drops to the 100 to 95 psi range, then can hold and not leak any more, with nothing connected. I’ve not yet timed how long it takes to get down to that range. This is with no hoses or tools connected. I’ve soaped all the joints but see no bubbles. Any ideas?

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  mark
December 27, 2016 12:19 pm

I suspect that you’ve got a pressure related leak in the tank check valve, which stops leaking once the pressure drops below that threshold. Empty the tank, remove, clean, test and replace the tank check valve. Did that make any difference?

Model-man-Chris
Model-man-Chris
December 10, 2016 12:48 pm

My iwata moisture trap leaks whenever I try to get about twenty psi. When I turn it up it will stop leaking air from the bottom stops leaking. The compressor is suppose to turn off automatically but doesn’t seeing how the moisture trap is leaking. Help please I am new to airbrushing.

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Model-man-Chris
December 10, 2016 7:41 pm

You are referring to the combination Filter / Regulator installed on the discharge line to the discharge coupler on the Iwata compressor? Have you, with the compressor off and the tank, if any, drained of air, removed the bowl from the filter and emptied it?

Brad Smith
Brad Smith
December 4, 2016 9:33 pm

My compressor holds air just fine but when i turn the knob to direct air to the attached tool there is a huge air leak out of the rear of the manifold. What do i need to do to fix. Replace manifold internals?

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Brad Smith
December 6, 2016 6:46 pm

Brad, by the “the knob to direct air” are you referring to the regulator knob? Does the leak continue after you turn the knob or does it stop. What make and model of compressor, please?

Brad Smith
Brad Smith
Reply to  Fix My Compressor Moderator
December 11, 2016 7:46 am

Kobalt Air Compressor F15DKL, F215DKL, or 232177 according to “mastertoolrepair.com” when i turn the regulator knob to send air to the air hose, a huge air leak is coming from the rear of the regulator housing. There is a flat plate with four screws that it leaks out of. I have dissasymbled, cleaned as well as possible but still leaks. It holds air fine until you try to direct air to the tool. Also was oily inside. Is that normal?

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Brad Smith
December 11, 2016 8:45 am

Brad, I couldn’t find much info on this F15DKL Kobalt, so I’m not sure that it’s oil lubed. From the image I would guess not. So, where did the oil inside the regulator come from? If not from the compressor then it must have been there when assembled. I did see complaints about the regulators failing on this model. I suspect the diaphragm has let go. Since I could not see if this regulator is in a manifold, or just attached to one, I cannot tell you how easy it will be to replace, yet since you can buy a new mini-regulator for $15 or so, it might be worthwhile doing that rather than spend any more time trying to fix an inexpensive, no-parts-available regulator.

Matt Green
Matt Green
November 24, 2016 10:49 am

Hi,

Bit of a newbie to this but, should a moisture trap always leak air to the extent that the pressure is always falling when the compressor turns off rather than waiting for a demand. Mine is leaking 5 Bar in 10/12 mins.

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Matt Green
November 27, 2016 5:25 pm

Nope, Matt. The compressed air filters (moisture trap) should only expel air when the manual valve at the base of the bowl is opened, or, if it is a float drain and there is sufficient water in the trap to lift the valve to open the drain.

Zac W
Zac W
November 14, 2016 3:21 pm

I have Rigid, 5 gal compressor. When I turn it off and unplug the power cord, the air releases out of the house or connector until there is no air or pressure left in the tank. I don’t know if this is a pressure switch issue or something else.

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Zac W
November 17, 2016 1:36 pm

Zac, I’m not quite sure what you mean by the “air releases out of the house or connector”. If that’s supposed to say hose, are you saying that when you plug the connector into the coupler, air is leaking out there? If so, you may have a mismatched coupler and connector. If the air is not leaking out there please advise where.

Doug P
Doug P
April 7, 2016 12:50 am

Hello. First, thank you for such an informative helpful site. Now the problem. I have an older 60 gallon Ingersoll Rand Compressor model IR5E6VA. Works great with the exception of the air that continually leaks through the oil filler/breather plug. From what I’ve learned here I’m suspecting the cylinder seals. I think that’s right? It leaks wether it’s running or not thereby depleting the pressure in the tank causing the compressor to cycle on and off. No oil blow by. What I’d like to hear is “easy fix”. Thanks again.

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Doug P
April 9, 2016 2:17 pm

The compressor symptom strongly suggests that the piston seals are badly worn or damaged. A little air will wick past between the piston and the cylinder walls all the time, yet as the seals wear or are damaged, more and more air gets through, and that air blows out the oil fill vent. That air is leaking after the compressor stops seems to us to be a problem with a leaking tank check valve, too. Easy fix? Depends on your skill level in tearing down the pump. The tank check valve is fairly easy, and that’s covered on a page on this site already.

George Goehl
George Goehl
February 29, 2016 10:44 am

60 gallon vertical tank. Plug in side is leaking. Removed and replaced the “O” ring and wrapped threads with teflon tape. Screwed plug in and tightened with 24″ pipe wrench. Still leaking. Any suggestions? Thanks,

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  George Goehl
March 1, 2016 10:54 am

Odd that, George. We’re not fans of teflon tape in air systems anyway. We suggest you try using a paste thread sealant, which offers more mass to help seal up pinhole leaks.

Denver James
Denver James
February 15, 2016 10:16 pm

Hello, I have a small dual tank compressor that sounds like air is coming out within the motor housing. Any ideas what that could be?

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Denver James
February 15, 2016 11:32 pm

Make… model? It’s hard to be specific without specific info. Offhand, we’d suggest you check the tank check valve to be sure it’s working.