air compressor Leak at pressure switch unloader

Good evening to everyone. On the day of the leak it was 0 degrees
Fahrenheit in Northern Illinois. The air compressor is a Sears craftsman
circa 1986?? I bought this thing on Craig's List about ten years ago and
it has worked flawlessly. I got zero documentation when purchased so I
am in the Dark as to model number and would appreciate any help in
identifying this model. There are two raised plates with numbers. The
first is a small 1 inch cylindrical shaped plate with 21 E 86. The
second is on the raised plate painted in the same red as the compressor
with either of these two numbers on it as I can't make them out clearly.
It is either 1102862223 or No 862223 with MFCS after them. Below
this there are the letters SH .094 and HD .094 then CRN
F0575.5123467890YT. From what I can see on the motor plate it is a 3 hp
electric motor and the unit is 220 volt plug-in.

The compressor leaks after it has reached pressure and shut off, its
very audible coming out somewhere around the pressure switch unloader
valve. A search puts it it at about 51-49 percent Tank check valve to
pressure switch as the problem. I removed the fitting where the tank
check valve should be but it looks like a clean fitting where there was
not a valve originally unless it has entirely disintegrated. Please see
picture. My problem is I cannot identify the replacement check valve
since I cannot identify the compressor. None of the numbers I have
listed comes back as a valid craftsman compressor model number. Please
look at the fitting I removed and tell me if you think there was a check
valve in there that just totally disintegrated? If you can help me out
with a model number that would be great also.

It appears my last two pictures of the tank check valve did not load so here they are.

If the leak is very bad I think I would just go ahead and replace the pressure switch.

Check with car quest for that valve.. replaced mine on c/h compressor several times. Think it was a schrader. LVP

I tried Carquest for a check valve for my compressor last summer. The first and second one they sent was wrong. They said they would order another one. After three weeks i gave up. They never got it. I went to northerntool.com and ordered the correct one.

Oops, sent email instead of reply. Ebay has a l o t of those just do a search for 'air compressor check valve'. You need one as yours is missing its guts.

The Sears number is probably the 110 number. They seem to like 110.xxxxx style for part numbers.

First off it is a DeVilbiss compressor probably made for Sears. Since sears had a lot of things made for them. Now I don't know if they are still in business or not. Should be able to get a pressure switch from any parts house to use on it. Beyond that I haven't any clue. I know Quincy sucks for parts through the company. I called them on an old compressor of dad's once with model and serial number they couldn't find anything for parts to it.

I think I have seen that check valve in the TSC display of air compressor items.

Found this on Amazon, they had a wide choice. Inspect that aluminum line carefully they often crack at the fitting, just at the Ferrell. It's 1/4 by 1/4.

I guess your pressure switch and unloader are working fine, but you need a new check valve at the tank, make sure you install it in the correct direction.

I think this might be the right one:https://www.amazon.com/gp/product/B00EYC4SG2/ref=ox_sc_saved_title_1?smid=A202MBZTDS9E1Y&psc=1

I went ahead and ordered the one wore Out posted about at around twelve bucks. Thanks Wore Out! I'll have to plug a side port but it should work fine.

If there ever was a check valve, it would have been in the big line from the compressor, where it goes into the tank.

There would not have been a check valve under the pressure switch, just to clarify that.

If there is not a check valve in the line from the compressor, the unloader depends on the output reed valves in the head to stop the back flow. Could be a broken reed, or carbon under the seat. The head will need to come off to access the valves.

So that begs the question, if I put in a check valve and there really was not one in there originally am I creating a BomB or will I just get a poor operating compressor?

(quoted from post at 10:28:34 02/25/22) So that begs the question, if I put in a check valve and there really was not one in there originally am I creating a BomB or will I just get a poor operating compressor?

Click to expand...

From your photo it certainly appears it left the factory with a tank check valve and parts dropped off, it would be very unusual if it didn't.

In any case, installing a new check valve certainly won't "create a bomb" or cause a "poor operating compressor".

Did you ever rock the unit around a bit and listen for loose parts in the tank as I previously suggested?

Also, the tank port is large enough to insert a "borescope" and have a look around, they are $15 and up on the 'net, or perhaps a buddy has one you could borrow (ASSUMING you don't have one).

Would (at least to me) be interesting.

Thank-you Wore Out for your continued assistance. I'm looking at
getting a Borescope, sure would be handy around a tractor. I have very
poor wifi in this rural location so would need a stand alone unit
although I could drag the compressor in the house. Appreciate the
suggestion.

The compressor reaches pressure and shuts off and it does have a working
safety valve. I'll stand far away. It doesn't hurt to ask about potential
exploding things.

I was wondering how the check valve is able to leak around the unloader
as there is only one line from the check valve to what I assume is the
Head Then there is a separate smaller line from the head to the
unloader which means assuming it's a wore out check valve the air is
traveling back thru the larger diameter line thru the head and out the
unloader line and out the unloader?

I don't live there full time so I have not been able to shake the tank
for rattling but do remember an internal rattle. There are also some
rather large plugs on either end I could remove and tip the unit and see
what comes out?

The tank check valve keeps air from leaking back out of the tank once the compressor shuts down
The unloader bleeds the air out of the line between the compressor and tank making in easier for the compressor to restart
Since you tank check valve is bad when the compressor shuts down the unloader trying to bleed the line continues to bleed the air out of the tank, since it can't completely bleed all of the pressure off the line when the compressor restarts it is starting up under load rather than having one to two revolutions of free spin before pressure builds back up in the line
This causes a higher amp load against the more and I've seen in some cases the compressor stalls out and trips out the motor overload

I just wanted to report that the check valve was indeed my problem, Not a drop of air leaking and after replacing valve, the new valve did change the length of the supply tube going into the valve and I had to cut about 1/2 inch off tube.