Compressor not releaving head preasure

They will run until the air pressure is at the max, then will shut off. This is normal. When you use the air & it goes below a certain level, the motor should run again. If the pressure is not reaching the max value, then the motor may be overheating.

If it were the check valve, (safety release valve), you would hear the air escaping from the safety release valve. You have an air leak somewhere. A small leak in the system will keep the compressor from building pressure. If you turn the compressor on and feel around the ends of the tube that leads from the compressor cylinder head to the tank (be careful... it will be HOT) you may feel air escaping from the tube connector at the tank or the connector at the compressor cylinder head. If that is the case, tighten the connectors at the compressor head and the tank. If the connectors still leak, you will need to remove the tube and replace the packings (gaskets) at each end of the tube. Also check all of the hose connectors for leaks, and check the hose for damage that may cause an air leak. If you remove the air hose from the compressor and run the compressor you will be able to tell if your problem is in the hose or hose connectors or the compressor-to-head air tube.

The pressure switch needs to be replaced.

Have a look at the check valve (you will find it between the pressure switch and the tank) Make sure there is no pressure in the tank before you remove it!!! There should be a spring and and rubber or plastic valve in there. Clean it up, or if necessary, replace it. Otherwise, you may need to check the valves in the head, if the are not seating properly then you will get the air passing through. It is very irregular for the air to get passed the piston rings in the pump, but try those things and post on here to let me know how you get on

Thanks
Carl

Check the pressure switch. The unloader valve is actually in the pressure switch where the small air line from the tank check valve attaches to it. When the pressure switch turns the motor off it then lets the head pressure bleed off so the motor can restart the next time pressure drops in the tank. If it's not working and bleeding off the head pressure the cold start valve (the one with the pin in it) also won't open so the motor can restart and warn up properly.

Could be leak or faulty valve plate in head. Use soapy water and spray all fittings including drain valve and pressure regulator. Repair as needed. If no leak found suspect problem with compressor. Try simple test, with compressor running and has reached max pressure (60psi) remove air filter and feel intake for suction. Be carefull could be hot. The suction should fairly strong. If no suction or actually feels like air is blowing out of intake, suspect valve plate. Parts are available at dewalt service center or www.toolpartsdirect.com. Good luck

take cover off pressure switch and you will find a hex head or a screw inside undo it to decrease pressure or do it up to increase pressure but make sure you un plug 1st

You stated that the compressor started up fine. I'll assume it reached it's max psi then cut out. Then upon reaching it's cut-in psi the motor ran slowly for a few seconds, then kicked off. I also assume you mean check valve when you refer to the non return valve.
If this sounds about right then. The first thing I would do is bleed out all the air from both the tank and the pump supply line leading from the pump head to the tank's check valve. You can do this by simply loosening the fitting that attaches the line at the head or the check valve. Once done try running the compressor again.
The purpose of this is to check the unloader valve. This valve bleeds off the pressure that remains in the compression cylinder and the supply line up to the check valve. When functioning normaly it will bleed off this pressure once the motor shuts off. If it is not working correctly then when your compressor starts back up (once it is already been filled) the piston will be working against a psi close to the max psi.

If the problem reoccurs only after the compressor has reached it's max psi, then the unloader valve is most likely the problem. If however it will not start up at all even after a complete bleed then it has to be something internal to the pump and\or motor.

Please try this and let me know (or repost) your findings.
If it's the unloader valve I should be able to explain how to repair this valve.
Good luck.

Yes,but if the max is 125 you don't want to increase it above 110 and set off the pressure relief valve.

Dont understand the question , does the engine shut off after p-max is met , or does it continue to run , if it continues to run then you have a pressure switch problem