Air pressure does not go over 25 psi I have taken the whole unit apart and check, relief valve,regulator,check valve. Pressure switch, Piston & Gasket. everything seem good I have taken the pressure gauge off and run the unit to check for blockage, none found. The copper line that connect to the piston Head and carry the air to the tank does get very hot within one minute of running the unit It is a Craftsman 4 gallon , 1 hp model , with very little use on it, it still look just like new Can you provide any tips. Thank a lot

replace the pressure regulator/ control unit

maybe you are reading the gauge wrong
the tank gauge and the regulator gauge will read the same but the gauge that reads when you adjust the regulator is the out line pressure to be n maintained during tool use

ASSUMING THIS IS AN ELECTRIC MOTOR DRIVEN SINGLE STAGE COMPRESSOR, IF THE COMPRESSOR USES OIL IN THE CRANKCASE, THE PRESSURE SWITCH SHOULD CUT OFF AT 125 PSI AS THE ACT OF COMPRESSION HEATS THE AIR QUITE HOT. THERE IS ALWAYS SOME OIL THAT PASSED THE PISTON RINGS IN THE COMPRESSED AIR. IF THE COMPRESSED AIR GETS HOT ENOUGH, THE OIL VAPOR CAN IGNITE AND THE FLAME CAN CARRY TO THE TANK FOR AN IMPRESSIVE EXPLOSION. THIS ORDINARILY DOES NOT HAPPEN BELOW 175PSI OR MORE.

OILLESS COMPRESSORS CAN BE SET TO 150 PSI. WITH EITHER TYPE OF COMPRESSOR, THE HOSE SHOULD BE ATTACHED TO THE REGULATOR OR THE REGULATOR STACK, NEVER TO THE COMPRESSOR, AS THE COMPRESSED AIR LOSES MUCH OF ITS HEAT WHILE IN THE RECEIVER. IF THE WHOLE TANK IS GETTING HOT ENOUGH TO MELT A PROPERLY ATTACHED HOSE, YOU HAVE A DANGEROUS SITUATION, CHECK THE OPERATION OF THE PRESSURE SWITCH, UNLOADER VALVE AND RELIEF VALVE. THE RELIEF VALVE SHOULD OPEN AT NO MORE THAN 150 PSI, THE UNLOADER VALVE OPENS WHEN THE PRESSURE SWITCH SHUTS THE MOTOR OFF, AND SHOULD ONLY HISS FOR A FEW SECONDS AS IT DUMPS THE PRESSURE ONLY IN THE COMPRESSOR AND THE LINE FROM THE COMPRESSOR TO THE TANK INLET CHECK VALVE. IF THE UNLOADER VALVE HISSES MORE THAN A FEW SECONDS, THE TANK INLET CHECK VALVE IS LEAKING AND NEEDS TO BE SERVICED, CLEANED OR REPLACED. IF THERE IS CARBON BUILD UP IN THE VALVE, THERE IS EXCESS OIL PASSING THE COMPRESSOR PISTON RINGS, REPLACING THEM MIGHT FIX THAT IF THE CYLINDER OR RING LANDS ON THE PISTON ARE NOT TOO TAPERED OR WORN.

I would guess from the info supplied that the pressure switch is shutting it down at 125. Most piston type compressor only pump a max. of 175 unless it is a special high pressure unit. Also it may be shutting down on high amps, high temp etc.However with all that said Piston units are positive displacement, meanning that it should pump until something gives. Start your unit, close the discharge air valve and see what it pumps up to. May have to adjust pressure switch to get over 125. If unit runs and runs and just will not go over 125, you probably have a valve going bad. Do you have a safety lifting. if so another indication of a bad valve.

Hi,
If the unit will only pump to 40 psi. then here are a few things I would check...

Check the air filter to make sure it is clean so air can be pulled in easily...
Check the relief valve to make sure that it has not gone bad and is releasing the air pressure or leaking at 40 psi...
Make sure the any hoses or nozzles are tight and not leaking...

If all of this checks out then the compressor has an internal problem such as bad rings or valves that will keep it from pumping to a higher pressure...
The pump will need to be torn apart to find the exact cause of the problem... and many times the correct replacement parts will not be available to rebuild those compressors..

heatman101

Here are a couple of things to check. While the compressor is running spray soapy water on all airlines, fittings, bottom of pressure switch, regulator and drain valve to make sure that they are not leaking. A small leak will prevent the unit from reaching cutout limit. Repair as needed. Next unplug compressor and remove cover to expose cylinder and piston. Move piston to top of cylinder and check for scratches or wear neer top of cylinder. If scratched, air is bypassing piston ring and will not reach cutout pressure. If cylinder looks good and no leaks then problem most likely is valve plate/ reed valves or head gasket. Problems within head will cause low pressure and air line to tank will be very hot. Bad reed valves will also cause air to blow out of intake when it reaches 75 to 80 psi. Parts are available at www.chpower.com or at www.toolpartsdirect.com. Good luck

I assume it keeps pumping, but doesn't build any more pressure. That is probably bad valves or rings. If your unit has a crankcase breather, and it is puffing alot of air, look for rings. Otherwise valves.

Replace check valve the piston is getting stuck sometimes alloying the air to leak all the way down till it comes back on

First remove the valve using probably about a 1/2" wrench but make sure there is no pressure in the tank before you do so. check the cone and seal by loosening the valve by hand and check for debris. If there is no debris then the problem is either the pressure relief valve or weak pressure regulator but may also be a bad piston seal if it is a direct drive unit.

I have worked on several of these little compressors and have found that they suffer from early failure of the cylinder and piston. However, you could check a few things for other problems that I have seen on low volume compressors. While the compressor is running spray soapy water on the airlines and drain valve to make sure that they are not leaking. A small leak will prevent the unit from reaching cutout limit. Remove the pressure regulator and attach hose directly to fitting to make sure the problem is not faulty regulator. I have not been able to find parts for this unit. Good luck, happy new year!