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.
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… Read more »
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… Read more »
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… Read more »
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… Read more »
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… Read more »
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… Read more »
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… Read more »
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… Read more »
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… Read more »
I think most air compressors have a compressor tank check valve manufactured by a third party. Companies tend to specialize anymore, I believe. Does your post ask why the screw cap on your compressor check valve fractured? If so, the reason I think is that in the drive to offer lower and lower prices for the DIY type air compressors, compressor assemblers tend to acquire parts from the cheapest source. A cheap source may not… Read more »