Every air compressor with a tank and unloader valve has a compressor tank check valve.
If you have had a chance to read the page on the air compressor unloader valve on this site, you will have already begun to understand why the compressor tank check valve is important to the unloader valve, and to the proper working of your air compressor.
Where is the compressor tank check valve?
Where is the compressor tank check valve on your air compressor? Typically it is located on the compressor tank where the line from the pump head reaches the tank.
In the photo above the tank check valve is seen within the red circle. The air line coming into the check valve from the left brings air from the pump to the compressor tank. The air line heading up and to the right is plumbed over to the compressor unloader valve.
Your tank check valve may not look exactly like the one in the photo, and, on many of the modern do it yourself type air compressors, the whole pump and control section may be entirely shrouded and you may not even be able to see where the air line from the pump head enters the tank. Still, that is where the compressor tank check valve is normally located, where the line from the pump reaches the tank.
What does the compressor tank check valve do?
Another name for a check valve is a one-way valve, and that’s what the tank check valve does.
I mentioned earlier that it works hand-in-hand with the unloader. The unloader valve periodically opens the line from the pump head to atmosphere for purposes of venting any air trapped over the piston.
If the tank check valve was not in this circuit, when the unloader valve opened, all the air from the compressor tank would bleed out the unloader valve to atmosphere too. The pressure in the tank would drop, the compressor would start, and then it would pump the tank up to the cut out pressure setting, the compressor would stop, the unloader valve would be opened by the pressure switch, and once again, all the air in the tank would bleed out.
The tank check valve prevents this endless cycle by keeping the air in the tank after the compressor pump has pumped it there, even when the unloader valve is open to atmosphere.
What does my compressor tank check valve look like?
Removed from the air compressor your compressor tank check valve could be similar in appearance to the one in the photo below.
In this typical tank check valve the small, bright male fitting on the left is where the line over to the unloader valve is connected. The part of this check valve above the red thread is inserted into the tank. The air line from the pump head would be connected to the female port not visible at the bottom of this one-way valve.
A non-functioning or poorly working compressor tank check valve is sometimes a problem for air compressor owners. See information on that under the fixing compressor problems tab.
Comments or questions about the air compressor tank check valve are welcome using the form below.
My name is Ron. How do you connect the air line from the check valve to the compressor switch? My problem,is, the sloped (curved) shoulder on the connection to the valve. Do I need a “special” compression nut and olive to make off the air line? The line I have is 6mmx4mm “plastic”.
I can not get the old check valve out. It come up about 1/2″ after I unscrew it. Thank you
Hi,
I’m from the Philippines & thank you very much for this great site. I learned a lot from the articles, specially this one about the tank check valve where I finally got convinced that it’s the remaining piece of the puzzle why my compressor is leaking out air not only to the pressure switch unloader valve but I can hear air leaking out too when I press my ear near the cylinder head’s air filter.
I took a picture of the valve & I suspect the air leaks thru the white silicon/plastic-like stopper ( whatever it’s correct name is 😀 ) back out to the intake & unloader pipes. Originally the surface of this white stopper had a circular impression on it from being continually pressed to the brass hole opening of the valve main unit. I tried smoothing it with a sandpaper but still the leaking issue persists.
My next move before surrendering & buying a new valve would be either to try putting an o-ring around that opening thick enough to make contact with the white stopper or if I can’t find one that fits I’ll be using that black rubber thing in the picture, or thanks to Juan from Venezuela I will glue a rubber to the white stopper, since rubber is a better sealant.
Hi, my old compressor check valve in dimensions is about 2″, the overall 3 1/8″, is a 3/4″ by 1″, it is assumed that the air flow is 0 – 60, if I use a 3/4 x 3/4 valve the air flow is going to be 0 to 30 cfm, the problem that I have now , is that new check valve is 3 11/16, and I have to install it on a 1 inch tee ,I think the length is going to be way to much for the bottom part , would it diminish the compressor performance or I may damage it? , if I use a 3/4 x 3/4 , otherwise I will have to modify the whole thing installing bigger 1 1/4 components for being able to make it work, please advice thank you
how do i remove broken check Valve that broke off?
Vertical Hausfeld 20 gallon compressor.
So the problem seems to be the check valve right? Removed the valve to have a closer look and found no flap, no spring, no mechanism to control back flow! I checked in the tank for debris or broken valve pieces and found nothing. Valve is identical to the one in the picture and the one at the beginning of this topic.
I found a replacement that is identical but cannot get any other pictures of the insides to confirm that there is actually a mechanism. Can anyone confirm that Im not crazy or totally missed something here.
Hi everyone, my name is Juan Borregales from Venezuela, I’m trying to build my own air compressor from a fridge compressor, the thing is, I was checking my tank check valve and I realized it was compomised, it was leaking air when I blew it, those kind of valves are very expensive here (like everything else) so I decide to repair it, I din’t open the valve I (it’s the type of valve that are sealed) but you could see the valve wasn’t seating , I took a plastic bottle cap and removed the little plastic (or rubber) from inside, I cutted it with a scissor the same diameter of the top end of the spring, then , pushing the spring down, I placed it inside the valve and now it’s seating, it’s not leaking at all, I put this information if someone need a quick repair of that valve, sorry for my bad English, best regards to all of you
I just wanted to thank you for building this site to share all this incredibly helpful info with everyone. Not every DIY guy has the money to throw at new compressors, hours of repairman bill, or even parts. However the better part of us can turn a wrench and McGyverize dang near anything. Haha.
My Snap-On compressor JUST went down yesterday! It was built by Sleegers, as mentioned in your section about Snap-on compressors. I was having the constant air leakage/drain from the unloader valve. It would stop when the compressor would start up and come back when it shut down. It also wasn’t present if the compressor was unplugged, in the auto position, but below the startup pressure.
I went through the unloader valve and it was fine. I then read up on this page all about the issues that people have when the check valves fail. I removed mine and found a buildup of nasty rust like crust on the valve (worse then what i am showing in the picture). I sprayed it down with PB Blaster (the only penetrating oil worth buying) in a paint can cap. I worked the plunger up and down and let it sit over night. Low and behold it now works perfect. When i first pulled it out i could blow back through it completely proving it was the culprit. Not anymore… I don’t suggest that though. It didn’t taste any better after its PB Blaster marinade then before. Haha!
I really put this compressor through its paces though… I ran my plasma cutter and various air tools on it consistently through the entire engine swap project on my 2007 Kia Sorento. It went from 3.8L V6 to an American monster… A 6.0L LSx V8! Sleeper is an understatement!
Thanks again for taking the time to build this site!!
I have a 20 Gal Husky 947265. Is there supposed to be a pin hole in the cap of my check valve. The tiny plug that unscrews has a pin hole in it. If I run the compressor, then unplug it, air leaks from a pin hole on this plug of my check valve. It is a continuous leak. Here’s the part (Part Number: E106123).
I just took my check valve out, and it had broken a coil off of the spring and jammed the piston/seal out of whack. Took it apart, stretched the spring enough to hold tension against the seal, cleaned it up, and reinstalled. Good as new!.
Ran across this article after removing my check valve because it had a small leak at the threads where it screws into the tank. It was a bear to get out, threads stripped coming out. Glad it was aluminum, so it did not damage the manifold it was screwed into. When I got it out, I noticed that both snap rings that hold the one way valve into the lower part of the housing had came out of their ring grooves and the valve was dangling in the housing. Ready to be replaced after 33 years.
Hi Willy,
Thank you very much for your information, After I read your website, it took me 2 minutes to locate and clean my check valve (Had to get anew one because the old one was damaged.)
Great site, very informative.
Just ran into the same problem of air escaping from the unloader valve once the tank was up to max and the motor stopped. I opened the check valve and there was a small piece of rubber sealant holding the check valve open. Almost went to buy a new compressor. Thanks for the tip.
My unit is a MAC2400 and is approx 10 yrs old. After reaching 120 psi it shuts off and leaks down to approx 80 psi at which time it stops leaking. Occasionally, after a few cycles, it stops leaking and performs normally.
I have started disassembly with the thought of replacing the check valve (which is difficult to get to). From some research it seems the check valve is a common failure, but there is the question of whether it might be the unloader valve. I regret that I did not find this site before starting disassembly.
Can you offer advice?
When combining two air compressors, for instance a 26 gallon one and a 21 gallon one, it says to install a check valve at both the compressors lines. 1) Does anyone know what that valve may look like or what it is versus other little ball valves I have seen for air compressor lines at the stores, and 2) where they want these check valves installed into the two compressor integrated system.
I would think they would go right there at the compressor, like before the line leaving the compressors and going to the tee. The tee meaning I am assuming a line leaves both compressors and go into a tee, then a main line leaves the tee and runs your tools.
As you can tell, I’m not too expert at setting up a 2 compressor system but I have a 3′ lead hose leaving both compressors and going into the tee, then a 25′ line going to a double filter thing for catching moisture, and at that point, another 25′ hose going to the hvlp gun or any other tools I need to run (impact wrench, die grinders, etc, etc) But I am really concerned about making sure my homemade system is as correct as I can get it for the painting of auto body parts and car fenders, hoods, whole car, etc, etc.
Thanks for any help. Btw, reason for all this is cant afford a 60 gallon or anything but I do have a gently used 21 gal from HF and newish 26 gal Bostich from WM.
THANKS again, very much so, for any suggestions, guidance, advice, etc!!
Excellent website, very clear and complete descriptions. My unloader valve leaks after the pump stops so I think this is the check valve. I will disassemble and try to clean the check valve, I assume clean with wd 40 ? Thank you for such good descriptions….
Just bought a used compressor. It has the check valve with an unloader valve. The unloader valve has a fitting where a small line is connected. However, the other end of this line is open or not connected to anything…it bleeds to the atmosphere. When the motor is running, there’s air bleeding out of this line continuously. Is this the way the unloader valve is supposed to work or is it defective? It doesn’t bleed when the motor stops as the predetermined pressure has been reached, so I know the check valve works fine.