Compressor will only build up to 40lbs tank pressure

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

Whats happening is the compressor is trying to start with pressure on the head/ compressor. The motor is not strong enough to over come the pressure so the motor tries to run ,may be hum a little and pops the breaker. When you bleed the pressure in the tank down the motor does not have to over come the pressure and starts up as it normally would. Now, your problem is the check valve between the tank and compressor. It needs to be replaced. It is allowing pressure in the tank back to the compressor. Thus the compressor tries to start and can't. Trace the line from the compressor to the tank. You should find the check valve screwed into the tank and the compressor discharge line screwed into the check valve. Remove the compressor discharge line,then remove the check valve. Assemble in reverse . also you can loosen the fitting at the compressor. if it blows air all the time it's the check valve for sure.

It sounds to me like you have a bad pressure switch. When these go bad, it takes less pressure to close or open the contacts to shut the motor down. You can get a replacement from any Ace Hardware. It will come with basic install instructions. Just follow those and you should be fine.

Check for a leak between you compressor head (pump) and your tank. Your pump output may be good but as your tank pressure gets higher the leak will not allow the tank to build up.

It could be that the input air filter is badly clogged. I might more likely be that the Non-return valve on the air tank input is not sealing properly and not allowing the tank to build up pressure. This valve is at the end of the main pipe runs between the compressor and tank. It could also mean (less likely) that the poppet valves inside the compressor cylinder head are not sealing properly. Other faults could be worn rings on the compressor pistons or a bad seal between the compressor cylinder head and block.

To check the Non return valve allow compressor to build up some pressure and then loosen union nut on Non return valve. There should be some air released at first but should stop if valve is ok. If leaking remove valve and check for dirt and clean. If valve still leaks replacement is the only fix.

Sounds like you have a stuck or broken reed valve in the compressor.

there is a box that is mounted on a direct line to the tank in the box is an adjustment you can make to build more pressure simply tighten in on the nut on top of a spring but never adjust compressor to build air past its handling capabilities.

There is a moisture release valve under the tank that may have been left open. If so, close it and the pressure will build. The reason the tubing heats up is because it is running so long.

Sirwriter

Your problem falls into one of two categories the first is the tank is leaking the second is the compressor is leaking. Try this run the compressor for a minute or two and turn it off if to hear a hiss the tapers off slowly your tank is leaking some were check the drain on the bottom of the tank, the pressure relief valve on the top or side of the tank and all other connections between the compressor and tank.

In the event there is no hiss this means the problem is the compressor you may have a bad reed valve or a bad check valve depending on the type of compressor.

hope this helps

check this blog for assistance. reed valves or piston worn

http://www.fixya.com/support/t1104466-craftsman_air_compressors