Help me figure out my Sears air compressor

[Crazy Legs]

Hey everyone,
I bought a Sears 80gal 2 stg air compressor in 2008 and its worked great up until this last couple of months.

Long story short a "reed plate" broke in the smaller high pressure head and the pieces junked out the check valve.

I ordered all the right parts from Sears and installed them yesterday, everything worked great, it pumped up fast but when it got to 105psi the pressure relief valve on the smaller 2nd stage head popped off on every stroke and wouldn't go any higher psi.

Its never popped off before, it has a "70" engraved into the side of this relief valve and i'm assuming it means 70psi but that doesn't make any sense cuz the pressure would be much greater than that I would think.

Anyway I took everything back apart and it looked great, no issues etc. I installed the old check valve in the tank and let it build back up and as soon at it got to 105psi the PRV popped again....

I pushed on the PRV on the head to hold it in and it continued to build psi above 105 just like it should but as soon as i let go it blew off like before.

FYI, It normally shuts off at 165ish and turns on at 145psi

I'm completely lost on what could be wrong.

 

[NUTTSGT]

Almost sounds like the PRV is bad. That should something easy to swap out.

 

[scooterseats]

On a 2 stage compressor there is a relief valve on the low stage to protect it when the inner stage pressure is too high. This is an indication that the second stage isn't doing it's job. From your description it sounds like there is still a deficiency with your second stage cylinder. I would revisit all components to check for other damage done when the discharge valve failed. Pay particular attention to the suction valve and and cylinder condition. Double check that all components are installed correctly and all sealing surfaces are sealed properly. Good luck.

 

[Crazy Legs]

My thoughts exactly but I figured that its never popped before & since I just rebuilt it all I'm assuming there is still something wrong.

Yes I would agree its on the PRV for the 1st stage even though its mounted on the high pressure head (2nd stage) - What is the suction valve? - Both cylinders look great, no marks or scoring, you can still see the cross hatching in the bores. Sealing seems good, I put all new gaskets on all the surfaces including both heads.
The only thing I didnt' replace was the 1st stage parts, I can't describe what they even look like, its a thick plate with 2 round little valve things that have lock nuts on the top side of the plate, but they seem to look good. Here is a pic of what i'm talking about

Does anyone have a better view of the exploded parts in this assembly? I'm stuck using the orginal manual and they aren't even clocked or rotated correctly in the manual. My model number is 919.167810 - I think when looking it up it goes by 16781

Here is a scanned in version of what I've got. I replaced everything in the RED balloon, the BLUE balloon is the valve thats popping at 105psi and they GREY balloon is the parts I did not replace. (Ignore the blue balloon around that LP gasket, its supposed to be red lol)

 

[Crazy Legs]

As you can see in the above exploded parts diagram from Sears the parts shown in the HP head aren't shown correctly. I'm wondering if i have something installed or clocked wrong...... I truely believe its right since I marked all the parts when I removed them but now I'm second guessing everything. Can anyone tell me the order of assembly on the HP head? Mine is Head, fiber gasket, then valve plate w/ reed, aluminum gasket, then valve plate with reed, then fiber gasket, then cylinder block. And the way I've got the valve plates clocked makes sense, the LP head pushes the reed down to let air into the HP head and then the HP side reed pushes up to let it out into the tank....... I'm lost lol

 

[Crazy Legs]

Anymore help with this issue?????

 

[kams1973]

Are the two reed valve plates identical?

 

[Kevin C]

You could remove the blow off valve that's located between the stages and run it just on the second stage to see if its working.

Even better would be to put a gauge between the stages to monitor the pressure across the high pressure head. Sounds like you still have a valve problem on the second stage.

 

[Crazy Legs]

kams, yes the reed plates and reeds themselves are identical.

I've got a gauge I could put in place of the pressure relief valve, I'm assuming it supposed to be less than 70psi for the 1st stage since thats what the PRV has engraved onto it?

And if its higher than that, that means the HP head is leaking into the low pressure side to trip the PRV right?

Because the Check valve in the tank is keeping the pressure in the tank rather than back feeding to the HP head as well right?

 

[mayday0017]

I like the idea of putting a pressure gauge in line with the PRV, this will allow you to see the actual pressure it is releaseing at. This will tell you a lot about what exactly is going on here...

 

[Crazy Legs]

I'll do that tonight and see what happens, stay tuned.

 

[Crazy Legs]

Ok here’s the latest, I went home and removed the PRV that was in the head and put in a spare gauge I had. Basically it worked flawlessly and pumped up all the way to 165psi and shut off just like it should. My main question is though, as you can see in the video the gauge on the head approx. matched whatever psi was in the tank. Obviously the reason why it was fluctuating was it was showing the cylinder in action intake stroke vs exhaust stroke. Here is a video of it at 100psi



So I guess it’s a matter of deciding if this is ok by having that much psi in between the 1st and 2nd stages. If so, then why do they have a low psi relief valve in the head from the factory? My opinion is I think the that gauge should be reading a lot lower psi. According to everything I’ve learned it looks like the compression from the 2nd stage is somehow leaking over to the 1st stage (where the relief valve is) but I can’t figure out why. But then I’m confused cuz if it was really doing that I’d think the compressor would have a hard time running cuz it’d be forced that air back into the system which would want to stop the compressor (putting a huge load on it) but it sounds and acts normal so maybe there is nothing wrong?

Oh I also took my temp gun to both heads directly on the surface right when it shut off at 165psi and to my surprise the bigger head 1st stage or bigger cylinder was 170 degrees and the smaller head or 2nd stage was 266 deg which I thought was high. But I also understand that the bi-product of compressing air is heat so I guess I’m not worried about that, but I still thought it seemed high.