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My air compressor does not reach full pressure. What parts do I need to replace to fix it?

Sears Craftsman Permanently Lubricated Air Compressor; Model 919.155731; 3.5 HP 25 Gal tank; purchased 10/92; The compressor runs well but it peaks at about 50 psia.and last year it went to 100+ psia. The air filter is missing, but everything else is as it should be. I do not hear any air leaks when the motor is not running, yet it will slowly lose the 50 psia over time. I have the parts list and the exploded view. It appears that the means of compression is an 'O' ring on the head of the piston. If I replace that plus the gaskets, will it resume its function? Is there something else I should do?

Air Compressors , Craftsman
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2 Answers from these members:
Joey S
Running the compressor without a filter can cause a failure within the valve plate assembly. I can't be certain of your failure but the valve plate assembly is no longer available. Replacing just the o-ring may not resolve your problem. If you do replace the 0-ring be sure to replace the head gasket too.
by Joey S Earned 1,944 community points in Craftsman
April 28th, 2010
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