"check valve" blew on 40400

by Nathan
(Houston, TX, USA)

I have a Central Pneumatic 2HP 8 Gal compressor (40400) about 2 or 3 years old. I use it only about once a month for a few minutes at most.

It just blew what is described as the "check valve" in the manual. Part of it that actually looks like the head of a bolt actually broke and shot off. I called the 1-800 and they said that the part was not available.

I have looked a bit online, but can't even see where I can buy another one. It looks like a very simple device. My guess is it is a pressure release safety valve that blows if the pressure is too high. I don't think that is the issue. I think it was more that the part was a bit weak, but if I get a replacement I will check the pressure and make sure.

Anybody have an idea on getting a replacement?

Bill says...

Hey Nathan... you talk about the check valve, but then, it sounds like you may be talking about the PRV valve.

Either should be available and they need not be necessarily the same brand.

How about another post with a photo showing what it is you are looking for? Actually, upload a couple, one showing where the device was on the compressor, and another a close up of the broken device.



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Jan 30, 2013
Same problem
by: Anonymous

Same with my 40400 which of course is out of production-the Harbor Freight way of doing things. The sent me an interchangeable pressure switch for 20 bucks and it did the same thing. I am stumped.

Oct 18, 2012
by: Anonymous

can this Check valve be plugged or bypassed it seems to be a weak part as i I have just inhiereted this comressor because of the same valve!

May 22, 2012
by: Nathan

Thanks for the reply and the offer of help.

I looked at the newer model from Harbor Frieght with the same HP and tank size and the part looked the same. When I got it it did have the opposite male/female threads, but I can find a fitting to fix that. The problem I ran into was removing the old part. It shattered. as I tried to remove the mail part stuck in the female threads on the tank, I broke one tool made to extract pipe in this situation. When I got another one I ended up denting the tank just pounding the tool in to place. At that time I figured I had done enough damage and I had better cut my losses.

Thanks anyway.

May 21, 2012
Check Valve for 40400
by: Anonymous Mike!

This site claims they carry parts for 40400, I have not find any negative reviews about them.


If the link wraps, copy and paste all of it carefully.


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Too Much Pressure

by Don

My compressor builds up to much pressure and the relief valve keeps going off. Is their an adjustment somewhere?
Hello Don...

The way it is supposed to work is that the pressure switch monitors the pressure in the compressor tank.

When that pressure falls to the cut in pressure setting the air compressor starts.

When the pressure in the tank reaches the cut out pressure, the power to the compressor motor is cut off, and the compressor stops.

In the case of your air compressor is sounds as though your pressure switch is not reacting to the pressure in the tank, and instead of shutting off the motor at the correct cut out pressure setting, the pressure continues to build until your PRV, a safety feature, lets go.

I suspect a failed pressure switch, and if this was my air compressor, I would not use it again until I had the pressure switch replaced.



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Air pressure valve stopped working

The rubber valve inside the unit is torn so the compressor runs but won't build up more than about 30 lbs of pressure.

I think i broke the switch when i tried to take it apart to find the air leak. Have been looking for some type of replacement but

#1) I can't seem to find replacement parts for central pneumatic and/or

#2) I'm not exactly sure of what parts I need or what their called. If more info would help I'd be glad to try to answer any questions but if anyone knows what I'm talking about and how I can fix this I'd appreciate the help.
If by the air pressure valve you mean pressure switch (see the pages about that to better understand what they are and what they do) then you can use virtually any switch that you can install on your air compressor, that has the same voltage range and interfaces with your unloader valve correctly.

You can see a variety of them in the compressor and parts store located at the top of both side columns.

Have a look at them, and then at the one you have now. Look for similar mounting holes, I expect yours is 120 VAC and most of the ones shown handle that voltage...

Or, take your existing one to the compressor store with you and compare the ones they have there.

There are only a handful of low end compressor pressure switch manufacturers in the world, and most of their switches are interchangeable if they fit your compressor.


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40440 - good workhorse with cheap parts

by Peter
(Ridgecrest, CA)

Finer threads than other parts available.

Finer threads than other parts available.

Finer threads than other parts available.
Definitely potmetal - it disintegrated.
I have the spring and washer, but never found the face of cap.

Central Pneumatic Compressor 40440 - good workhorse with cheap parts, check valve seems to be one of a kind.

The important parts on the 40400 compressor seem to be tough, it’s the small parts that are cheap and break.

My very first compressor coming straight out of the box leaked like crazy: it would not shut off, because it couldn’t fill up. The next day I drove 85 miles (and that was one way) to where it was purchased and HFT did replace it, only after I told them how far away I lived. Luckily, the replacement has lasted me almost 8 years, unfortunately, with minor breakages.

First, the cheap plastic switch on top of the regulator broke off in the first 6 months, then within the first year or so the petcock broke, later the regulator’s body cracked. I didn’t buy the extended warrantee, so I ended up just taking those parts off.

I decided to buy a smaller regulator from HFT, but it didn’t fit and I still have it sitting in the garage – the gas would have cost more than the part to return it. I just went without all those parts for the next several years.

My 40400 compressor always had a very slow leak even after I used Teflon tape on the drain valve, which helped and I even put Teflon in the actual quick connector, which also helped until the tape got broken after a few rounds of putting the hose on and off – too much time and trouble to keep having to re-tape. Great prices, but the tolerances are inaccurate, especially on HFT’s quick connects.

Several months ago the leak got worse, but I could not locate it and thought maybe it might be leaking inside the engine itself. I haven't used the compressor much, and only briefly when I did, so I let it go.

Finally I noticed the leak was at the check valve, so I carefully tightened it with a wrench (I applied hardly any pressure at all) and it blew. What cheap pot metal, I believe it was cracked the whole time only to get worse over time, I found the spring and the washer, but not any part of the face (or head) of the cap/plug. It must have disintegrated.

Now, I have searched many auto stores, hardware stores and everywhere online for months, but no other brands seem to have the same thread pattern, or are a different shape altogether. All I really need is the ¾” bolt-like plug (or perhaps it is called a cap), but the only similar parts I saw have a coarser thread. There are two sites online that have this model listed (40400), but state that there are no parts available other than a blow gun. I noticed they have other models of Central Pneumatic 8 gallon, 2 HP units (different numbers and shrouds), but don’t have a check valve. There is a part called “Unloader, Pressure Switch”, but it isn’t the same.

I am afraid, if I order something that looks right online, it would have something wrong such as the ones I have come across and would be a waste, because I would like to put the funds into a new compressor. Has anyone had any luck replacing the 40400’s check valve? If so, can you please share the brand name with us and where to get it? That boat from China really seems to be sunk.
Peter, I share your pain.

What we save in buying a cheap air compressor initially is often used up in dealing with all of the problems that poor quality provide, including, in your case, driving the 85 miles each way.

However, it's a trap we all fall into, and you need to resolve the problem.

That check valve purpose is to keep the air in the tank when the unloader valve is open (that's when the compressor is stopped) so any check valve you can screw into the tank would do this. The unloader valve line is upstream from this check valve.

So, visit the plumbing store, find an in line check valve with the same threads, use brass fittings to modify it to accept the line from the tank and the tee over to the unloader, and you are good to go.


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Jul 20, 2014
There is hope!
by: Bill

William, thanks for this contribution.

More and more we see versatile and clever folks coming up with parts solutions that are "out of the box" for the many air compressors on the market today that are not well serviced with spares.


Jul 20, 2014
Harbor Freight compressor check valve
by: William

I have the 21 gallon upright harbor freight 110v compressor, with the red tank and back motor housing . I was having bad check valve symptoms. Just to be thorough, I pulled the check valve apart to see if there way anything I could do, when I removed the check valve bolt, I found the spring and plunger were fine, and there was a piece of air filter foam lodged in the valve. I removed that, and checked the air filter on the compressor, it had completely disintegrated and was missing.

So, I cleaned the valve, put it back together, and went to home depot and bough a briggs and stratton lawn mower filter, cut the yellow foam to match the harbor freight filter housing and I am back in business. Also changed the oil while I was working on it. Maybe it will last me another 8 years :)

Just want to share this with everyone, as it may be as simple on yours. Don't just assume the valve is completely shot.

Apr 12, 2014
Here is the part you need
by: Sean

Hi hello saw this tread off from Google. here is the part you guys need.

Mine blew up today also and disintegrated as well. the part seems very cheap and low quality.

Here is the replacement from Ebay.


You're Welcome :)
Thanks for the tip, Sean. I hope it helps a bunch of folks, and Brian found it on Ebay some time ago as well.

If folks want to see this check valve, please copy the entire link and paste it into your browser.



Nov 09, 2013

I found one on Ebay for 14.95 with free shipping

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