I’ve got an 80 gal upright Black Max at the shop. It has a 1/4” line going to the pressure switch from the check valve of the tank inlet where the compressor pumps to. The small valve has an air leak all the time now. Everything still works but it bleeds down the tank overnight. I’m not sure if this valve should have pressure on it after the compressor shuts off and the check valve stops the air from the top of the tank. I’m wondering if the check valve is what’s bad and it’s letting too much pressure back to the 1/4” line and the pressure switch. I’ll post a picture of the pressure switch and line. This little valve is called an unloader valve.