Kleinn Air Horns 2121 120 PSI, Sealed Pressure Switch with Lead Wires is a heavy duty tank-mount pressure switch with 12-gauge lead wires. It determines the on and off pressure of your air compressor. The pressure switch is wired by relay to the compressor and turns the air compressor on and off automatically. The pressure switch is 90 PSI on, 120 PSI off and is sealed and potted for resistance. Too Loud? Too Bad.