Thanks for the post!

Your tank Check Valve is probably the cause of the leak. This is the one way valve that is in the manifold, which the Pressure Switch threads into, as well as your Regulator and Pressure Gauges.

You can view the full breakdown of this compressor on our website by clicking on the below link:

www.mastertoolrepair.com/portable-oil-fr...602710-p-747239.html

Also, you can view a video on how to test your Check Valve by clicking on the below link:

www.mastertoolrepair.com/how-to-test-check-valve-p-22524.html

If the ball and spring valve isn't closing when the unit shuts off, you will get back pressure from the tank and it will typically leak out of the small Unloader Valve weep hole which is on the side of the pressure switch.

Try this test and reply to let me know what you find.

- MTR

That's what I figured, good deal.

You can take this Check Valve (#6 in the diagram) apart and clean it, this may rectify the problem. At the bottom of the Manifold #11 on the diagram) you'll see the brass adapter which is the Check Valve; there is a ball and spring inside. The Discharge Tube from the Pump Head threads into the bottom of the Check Valve. There may simply be debris or rust which is not allowing the valve to close all the way after the unit reaches pressure and shuts off. Try cleaning it up first, but it may simply be that either the ball and/or spring are missing, which would obviously mean replacing it with a new Check Valve.

Hope this helps.

- MTR

Thanks for the post!

Actually the Piston/Cylinder Kit is still available through us. The part# is 048-0074M and it's $89 + shipping.

You can view it and order it by clicking on the below link:

www.mastertoolrepair.com/piston-cylinder...048-0074m-p-323.html

- MTR