Also, you may want to clean the brass Pilot/Unloader Valve. If there's debris or build-up in the Valve, the stainless steel ball inside will not seat. You may want to do this as it's possible this is why you're getting the back-feeding air to the pump.

www.mastertoolrepair.com/pilot-valve-for...e-rcb-style-p-2.html

- MTR

This is a problem that some Emglo units have experienced throughout the years, and obviously it can be very difficult to pinpoint the root cause.

The Unloader Valves in the head are operating as long as they spring back down easily after you pull the stem of the valve up. As long as the seats are clean and the o-rings lubed there's no need to replace them.

I would say that your Valves are *probably* okay. You can install a Check Valve, which will help, but my money is on the Pilot/Unloader Valve not operating correctly.

I bet the pressure that's back-feeding to your pump (and out of your breather) is coming from the small Bleeder Line that's attached to your Pilot Valve. These are notoriously difficult to repair. Again I would attempt to take it apart, clean it and make sure the stainless ball seats properly. If not, then the only option is to replace the Pilot Valve, which sell for about $39 or so.

My money is on that Pilot Valve.
Again, hopefully this gives you enough info to get this mystery solved!
- MTR

It's also a possibility that the Rings need replacing, true. This problem is difficult to diagnose. I know it's frustrating but there are just so many possible reasons why this could be happening.

Make sure the Valve Plate is not upside down, too. I know this seems it should go without saying, but I've done this before, which can cause this issue.

If you install Rings in the Pump and replace or clean the Pilot Valve, I would certainly think your problem would be solved.
- MTR