The On/Off Pressure switch is set to trip (close) at 27.5 +/- 0.5 PSI as the pressure descends. The Low pressure limit switch is set to trip (close) at 24.0 +/- 0.5 PSI as the pressure descends. When the pressure drops to the set level, the On/Off pressure switch turns on the compressor. When the pressure reaches the level that matches up with the switch hysteresis, it turns the pump off. If the pressure drops below the set level for the Low Limit Pressure Switch, it sends a signal (active low) out to alert the CTA.