Air leak when stepping on brake pedal

What you're describing would cause a problem with the park brake released and service brake NOT applied. Air leaks into the service side when none should be there. His problem only occurs when applying the service brake.

 

Yes sir no doubt. Normally. But, iI just ran into situation in a ‘94 Pete were it leaked like you said. Very slowly and quietly thru the BP-R1 valve. Very small bubbles when tested. But, with the park brakes released when you hit the foot valve or hand valve it would exhaust air thru them rapidly. Head scratcher all day. Checked all cans. Good. All lines for leaks. Good. So i started cracking fittings open and got to the QR valve and it was blowing air thru it when it shouldn’t. Totally leak free on outside. Found the diaphragm inside the compound port was 99% gone. Replaced valve and all is golden again. Strange for sure. New one in my book. $14 part after 10 hrs of troubleshooting,cussing , and head scratching.