After ten # pressure It then blows air out intake.

by James G Rowe
(Englewood FL. USA)

Have replaced pressure reg valve and checked check valve operation ok. I have removed head to check reed valves and could find no problem. If pressure pipe removed from ck valve it produces air pressure and air intake works correctly. As soon as air pressure pipe is blocked it blows air out the air intake. This is a craftsman Model #921.153101 1.5 HP 125# PSI

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Bill says...

It is, I think, the absence of back pressure that allows your compressor to run normally when you have the line from the head to the tank removed.

When you reinstall that line, and pressure begins to grow in the tank, that will create some back pressure, either affecting a failed or failing reed valve or blowing through a gasket that withstands lower pressure, but can't handle the pressure increase due to the building pressure in the tank.

It's my opinion you've either got a valve or gasket failure.

Good luck.

Bill