The Potter PS120 Series Supervisory Pressure Actuated Switches are designed primarily to detect an increase and/or decrease from normal system pressure in automatic fire sprinkler systems. Typical applications are Wet pipe systems with excess pressure, pressure tanks, air supplies, and water supplies. The PS120 switch is factory set for 120 PSI (8.3 BAR) normal system pressure. The switch marked with the word LOW is set to operate at a pressure decrease of 10 PSI (0.7 BAR) at 110 PSI (7.6 BAR). The switch marked with the word HIGH is set to operate at a pressure increase of 10 PSI (0.7 BAR) at 130 PSI (9 BAR).