Hey! This site is reader-supported and we earn commissions if you purchase products from retailers after clicking on a link from our site.
Question by Ron
(St. Gabriel, La.)
I have a model 921.153101, 1 hp, 3 gal, 125psi compressor. It will only pressure up to 35 psi.
Everything in the compressor looks good. Even checked to be sure the cylinder walls were not scratched.
I went ahead and changed the reed valves and replaced gaskets. Still doing the same thing.
Ron, you’ve nailed the first two of the issues that can cause an air compressor to run, and run, and not build air pressure by replacing the reed valves and gaskets in the pump.
Assuming that the valve and gasket replacement was successful, and there are no leaks to account for air loss, then I would guess that the cylinder seals may be going.
When the air compressor is running, do you have air blowing out of the oil fill tube cover? Please check as, on an oil lubed air compressor, weak or failing piston seals are diagnosed by air bypassing them and into the sump, and then up and out the oil fill tube vent.
Let us know, would you?
My Craftsman 1 HP 5 gallon has a reed valve problem
Question by Jaret
How do you replace the reeds for this type of compressor?
Hello Jaret. Thanks for writing in.
I haven’t dismantled every single air compressor to know specifically how the reed valves in your compressor are removed and replaced and since you’ve not included the Craftsman compressor model number, I’m having difficulty even checking how on your behalf.
Ask your local Craftsman store where they get their air compressors repaired under warranty. Contact those folks, and get the straight goods from them or comment here with your compressor model number and we’ll see if we can help.
Bill I have exactly the problem you describe with my 921, air coming out the oil cap vent hole and not building pressure. I have not as yet changed any parts. What should I tackle first? You say change the piston seals, do you mean the piston rings? I don’t see anything called piston seals on the parts sheet.
Ed, if air is flowing out the oil fill tube in the compressor is not building pressure, that’s a sure sign that air is bypassing the piston. There must be some sort of seal on the piston or in the cylinder wall to separate the oil in the sump from the air going into the tank, and air is bypassing it/them. I suspect you’re also getting oil from the sump going into the tank.
When you’ve disassembled the pump assembly to check, what are finding regarding the sealing method between the piston and the cylinder wall?