I picked up an old 1 hp comp (cast iron pump, twin "hotdog" tanks, a real Dayton 1725 rpm, 1hp motor) several years ago. This compressor used pneumatic actuated valves on the compressor - motor ran continiously. I changed it over to a conventional pressure regulator / check valve / pop off valve. I bought the check valve (w/ unloader port) at Grainer:After about 25 on/off cycles the valve sticks open when the compressor is not running - air escaping thru the unloader valve - so the compressor now cycles on once every min to 90 sec with a compress time of (guessing) 20-25 sec. when there is no air usage. I whacked at the valve with a 3/4 inch bar stock - no hammer close by and with each whack the air flow reduced. After about 3 or 4 whacks the air leakage was gone and the comp opperated correctly during cycling - for a while and then it started loosing air at the unloader valve.
I'm working on reroofing a house this weekend and I can't keep on running down the ladder every time the valve sticks. I also do not want to leave one of my other (better) compressors outside in the backyard of the house that I'm working on. I'm tempted to open the valve up - it looks like the check valve parts are inserted from the side that has the large hex. So, what is inside of a check valve - tiny loose parts that will spring out at me and get lost? Right now its a pain in the ass, but if I take the valve apart and can't get it to work it will be a much bigger pain to be with out a compressor.