On Tuesday when I was putting my compressor back together the check valve leaked noticeably. After several attempts to clean and polish the faces to mate I gave up and dropped an O-ring into the valve to seal it up until I get a replacement valve.
It got to bothering me though. In all the time I have owned the compressor I don't think that check valve ever really closed up perfectly. If I happen to be working outside on a day when I had the shop shutdown and the air valve turned off I would notice the compressor would cycle on at least once in a day's time. I just lived with it, and if I was going to be out of the shop for more than a couple days I would turn the compressor off entirely.
When I turned off the air and closed the ball valve Tuesday night the compressor gage read 145. Wednesday morning it had dropped maybe 2 lbs. It was still above 140. I think that's an order of magnitude better than it ever was before. It was about the same today. It got me to thinking.
You might recall I mentioned the plastic valve looked like it was made of PEEK. PEEK is a pretty hard plastic. In 3000 PSI air guns Acetal is often used for the valve against a brass or aluminum seat. PEEK is sometimes used in higher pressure airguns because above around 3500-3800 PSI Acetal may start to "flow." Those valves are typically a tapered plug that fits into a different angle or even edge radius tapered hole. The has a minimal contact area for sealing but because its a plug in a hole pressure causes it to center and seal pretty well. I've got a 3000 PSI Marauder in my back shop I haven't had to refill in nearly a year. I use it for pests in my garden.
Anyway, I was thinking it might be useful to design my own compressor check valve using acetal instead of PEEK using proven valave tech like that in an air gun. PEEK might just be to hard to form a good seal easily at the low pressure of shop air. Sure a plug in a hole design might stick a little more than the "flat ring" design the compressor manufacturer used, but the pressure differential should quickly over come that. Peak pressure might show a smidgeon high until the vale opened, but not for very long. As soon as the valve opened up it would equalize pressure and flow fine until the compressor motor turned off.
Since there is an unloader the compressor would never sit with excessive back pressure.
Heck at the relatively low pressure of shop air even HDPE might work as the valve against a smooth metal seat.
I don't mind buying a check valve. I actually already ordered 2. They are $10 each and some change. I just don't want to install one to have it be just the same as the old one.