Sounds to me that the brake pedal supply is taken off the same supply to the parking brake button. So when you push on the brake pedal, the air pressure drops enough to pop the parking brake. Look into rerouting the supply for the brake pedal, or reroute the sensing air supply for the parking brake so neither affects the other. I would not install a check valve-the parking brake has to be able to be bled off-with a check valve the pressure would remain the same even with an air pressure failure. Good Luck, TomC
Yeah, I feed air to my push-pull switch direct off both tanks (with check valves at the tanks so if there's a leak on the compressor side of one tank, it won't "back feed" and drain both tanks - at least not immediately, giving time to get off the road). Of course, there's a low-pressure sensor on both tanks so if one is going down, the buzzer will be squealing.