Check Valve Test
1)Let your compressor pump up to pressure and shut off.
2)Turn off compressor.
3)Find the large supply line that leads from the pump head into the tank.
4)Slowly, start to remove the supply line from the pump head.
5a)If you hear air coming from this line, then you have a bad check valve. Go to check valve page on this page link:
http://www.mastertoolrepair.com/bcompressor-accessoriesb-check-valves-c-25_4.html5b)If you do not hear air coming from the tank, you have a leaky pressure switch. Order a pressure switch or unloader valve on this page link:
http://www.mastertoolrepair.com/bcompressor-accessoriesb-pressure-switches-c-25_2.html