I have a Craftsman air compressor model 919.156520. The panel knob of the regulator fell off. I screwed it back on. However, now when I turn up the outlet pressure very little air comes out the hos

SOURCE: I have \an Air Comp. Model 919.167210 Craftsman

you can go to, sear web page for parts brake down and part number. when you log in, look at the top right for parts, than type in your model number. check your tank valve, if it don't close, air well leak back.

SOURCE: Bostitch 6 gal compressor regulator knob is broken

Call Bostitch At 800-556-6696 and they will send you a free redesign part #27. It was a bad design part and I just did it a minute ago.

SOURCE: Makita MAC5200 Compressor. Leaks

There are two types of regulators used. One has a rubber diaphram sealed at perimeter with body and a piston type. Most likely you have the piston type. Remove body containing piston/ spring mech. Examine piston lip seal. Lip will face toward body of reg. and must fit snugly into cylinder. Make sure cylinder is smooth and is well lubed.
If seal/piston fits loose remove seal and wrap some teflon tape in groove and re-install lip seal /test for snug fit. Notice small metal actuator extending from center of reg. , if it is circular (about 1/8 dia) then there should be an oring of the same size mated/fit into the piston. If this oring is missing it will leak as you describe. Lastly, there should be a gasket or oring sealing outer shell to body. If you have diaphragm type look for holes, tear or shrink too small. Parts are at www.toolpartsdirect.com or Lowes in the plumbing department good place for orings and silicone lube. Good luck

SOURCE: I have a Porter Cable

Replace the regulator

SOURCE: Craftsman Air Compressor 919.156640 -- Today, when

You could give it a try you don't have anything to loose and you might be able to clean it and thats what it sounds like. But you can redo bolth of the regulators with new ones get rid of the plastic cover and they thread on a pipe that comes out of the air system. You could get two new gauges and a manifold body for 50 dollars at a place that sells auto paint supplys or spray equipment. If the compresser still works good its worth it you just have to do a little retro fitting these parts tend to be vary standard its your call good luck

Testimonial: "Thanks. If I can't get it to work by my attempt at cleaning, I'll certainly follow your advice."