99 Volvo cummins engine automatic

this is pressure regulator valve, this control the pressure coming out the tank and what shows on the gauges the one on the screen is from the air dyer and it shows what the compressor produces

also on those pressure regulator valves where the little plastic cap is if you pop it off with a screwdriver in the center there is a little allen key you can adjust the pressure up or down just be careful though with the little allen key though so if your gauge is reading to high or low you can adjust it this way