by Peter
(Ridgecrest, CA)

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.

Central Pneumatic model 40400 air compressor

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.
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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.