I have a 2hp/4gallon compressor.I turn the valve all the way open,but can only get 40psi,and it keeps on running never increasing pressure.It maybe the filter,if you think it is can you please tell me where to find it.Also,I've noticed hot air coming out of the back.It is stronger on one side than the other,is this normal to do that.I have a roof to do this week,and can't afford to buy or even rent another one.Thank you for anyones help.
It is definitely the little spring steel flappers in the head. They are similar to the reeds in a 2-stroke motorcycle engine -- if you've ever had one. They open up a little to let air in on the down-stroke and close off the air intake port on the upstroke. Probably just a piece of one has broken off and it will allow the compressor to pressurize the tank somewhat depending how much of the flapper has broken off. You will notice that your air gage needle on the compressor pulsates when it comes up to the maximum pressure it can attain with that piece missing.
There are two different sets of the flappers in the head -- one for air intake and one for allowing the newly compressed air into the tank. Buy them both and a new head gasket or "O" ring.
Good Luck, Richard
Well I can't promise you this is the answer on yours, but I have the same compressor and it would pump up to about 60 psi and just sit there and run. I tried everything and ended up taking the compressor off the pancake and turn the compressor until the piston is all the way to the top. Take the 4 small bolts out of the head and there is a valve plate between it and where it mounts on top of the piston. Be careful not to damage the o'ring that is between them. There are three little pancake looking flappers under the valve plate and chances are one of those or more are broken off, causing it to bleed by and not pressure up to the normal 125 psi. If it's not that and not the little rubber isolator that hooks on the end of the feed line that goes into the head, I can't imagine what else it could be. Either one of these things can make it bleed by, causing it not to pressure up correctly. You might have to replace the head gasket when you do this. The valve plate is about $14.00, and the head gasket is $8.00 and the isolator gasket is somewhere around $2.50. I really hope this helps, and I have a feeling that it will if you haven't already gotten it fixed. Let me know if this does the trick.
On the air intake is located the air filter Unfortunately it sounds like your valves or regulator is weak not allowing it to build pressure
Based on these posts I decided that my reed valves were bad so I took off the cylinder head. Turns out the seal on the piston had folded over on one side and scored the cylinder badly. The whole cylinder was badly scored. My guess is that I didn't clean the air filter enough? That may have led to scoring and the subsequent breakdown of the teflon coating which eventually destroyed the piston ring? I frequently used it in very dusty conditions, doing bodywork and such.
The good new is that the reed valves are fine. :)
Maby more infomation about your question in Denair air compressor
I don't think its the filter,
first make sure the drain valve is closed, although the hot air coming
out may indicate you have a ruptured seal.
You can order replacement parts by going to Sears.com and clicking
on the parts link.
You can also order by phone a 1-800-4my-home 1800-469-4663
I have the same problem with a 921153101 craftsman compressor, when I opened the head everything looked fine untill I took the small brass plate off the top and noticed that the gasket had blown out inbetween the air intake side and the tank fill side. I bought all the parts gasket kit piston 2 sets of reeds etc from melco on ebay for $52 including shipping. Havent put the gasket in yet so I can check but I am pretty sure thats what was wrong.
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I have same problem and it's not the filter? Drained the water. Still nothing above 40PSI
I have the same problem on mine (15gal 3hp). After replacing the regulator and that didn't work. I took apart the plastic housing and found that the copper tubing coming from the pump to the tank has a rubber piece at the head has failed. This tubing just rests in it. Doesn't look like it would be too much. But you would possibly also need to replace the head gasket also minimal in cost.
craftsman Model# 921.153101, 3 gallon 1.5 hp
It pumps up to 40psi and then just keeps running. I checked oil level it was ok. I checked air filter it was ok. The tank holds pressure fine while running and when turned off. It is not overly hot only warm.
I checked for air leaks all around unit could not find any.
I purchased this in 2005 and have only used it a handfull of times to pump up tires and blow dust off stuff. It still looks like it came out of the box. The filter had now dirt or dust present.
Does anybody have an answer?
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Craftsman 3 gal Air Compressor, 1.5 hp, Horizontal Model #921153101
It won't pressure up. It use to pressure up to about 40lbs but now it won't pressure up at all. I have checked for leaks and found none. I have taken the head off and inspected the reeds and they are fine (not broken just some oil on them, very minor). You turn it on and it just runs with no air pressure movement. I check the check valve it was ok.
I turned the machine on with check valve out and it is blowing air into the tank. It pressures up a very small amount because I can pull the ring on the relief valve and air blows out.
What do I do next. I went to sears service center and they told me no techs on site. Have to send in and it cost $30 and then plus repairs with no guarantees it will be fixed. They offered me a reconditioned on at $80. A brand new one cost $99. Should I just throw it away and go to walmart. Or is there someone that can help.
Thank you
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