Craftsman 3 Gal compressor not building more than 25 psi

by Bob Hall
(Browns Mills, NJ)

i have read your posts and and tore down my compressor. both reed valves are fine, gaskets look new, piston rings look fine to me, checked the littel white valve that is in the copper tube that goes to the switch ....what else should i runs but holds at 25 psi...note that due to not draining the air after use, i found alot of dirty water in the tank when i removed the drain valve...could this have caused any damage to the unit? what else should i check and how would i check it?

Bill says...

Bob, good effort in trying to figure out what's going on with your Craftsman compressor, and for the complete post. It helps me try to help you.

You say the air compressor holds at 25 PSI. I take that to mean that the compressor keeps running, and the pressure never goes past the 25 PSI, or does the compressor stop at 25PSI?

If the latter, it's the pressure switch, I think.

If the pressure builds to 25 PSI and stays there with the compressor still running, and the motor doesn't seem to overheat (indicating overload) then you have a pressure related leak I suspect, and even though the valves and the gaskets look good on visual inspection, I think that under pressure one or both of these items are leaking.

Use a lighted match at the intake port to see if any air is huffing out while the compressor is running.

If not, then I'm going with a pressure related gasket failure.



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Feb 13, 2012
Craftsman Compressor
by: Phil

I have a Craftsman Compressor, Model NR 921-153101 that runs but will not fill the tank.The only thing I cand find wrong is the Preasure Relief Valve attached to the Preasure Switch is leaking air from a small hole beneith the valve. I have been to Sears and Grainger Industral and the valve cannot be purchase as a stand alone item. You must purchase the Preasure Switch to get this part. By the time taxes and shipping are paid the switch cost over $45. I can buy a new compressor from Harbour Freigh cheeper that that. Must admit I leary of stuff from them.

Phil, from what you have written, I suspect your check valve is leaking. Don't buy any parts yet. Empty the tank, remove, clean and replace the tank check valve. See if that solves the problem.

Aug 08, 2011
still confused
by: Anonymous

got it all back together (correctly i hope) and still no good....there is air coming out the fuel filter that would mean bad valves right? but my valves look there something that could be wrong with them that i cant see?

i cant seem to definitively say i see any leakage from the gaskets also...kinda hard to tell with that big fan even though i tried to block it off...

quesion of the thin metal gasket between the two valve corner of the two openings has a slight rise in the shape of a triangle...ho do i know where that should face? do i need to oil and of these valve parts or do anything special..used a little to hold the reeds in place

Aug 08, 2011
more details
by: Anonymous

youare correct in that it keeps running...not sure if it would overheat as i never left it running more then10 seconds after pressure stopped building...will try the match trick and get back to you...where exactly do i hold the match near the intake...i dont actually see any holes where it can be getting air into it? wil lthis test be affected by the air being blown by the big fan blade in the front..when i looked for leakes there was alot of air moving around which seems to be from that fan


Remove the intake air filter which will be somewhere near the top of the pump. Feel for air blowing out of that hole ( a lot or a bit ) while the pump is running. If air is huffing out, your intake valve is leaking. If the match doesn't work, block the external air flow with your hand, and drape a small piece of tissue paper near the intake. Careful it doesn't get sucked in.

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The Craftsman compressor will not build pressure

Compressor runs but will not build pressure. It feels as if the air is coming out of the intake port (through the filter.

Bil says...

Have a read of this page about about why a compressor won't build pressure.

I think you'll find your answer there.



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