The Potter PS25 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; air/nitrogen supervision in dry pipe and pre-action systems, pressure tanks, air supplies, and water supplies. The PS25-2 has two switches. The Low switch is factory set to activate at approximately 18 psi (1,2 bar) on a decrease in pressure. The High switch is factory set to activate at approximately 28 psi (1,9 bar) on an increase in pressure.NFPA 72 requires a supervisory signal for both high and low-pressure conditions. The PS25 is factory-set for a normal air pressure of 23 psi.