Air Differential Pressure Switch with a potential free changeover contact shall be used to detect the status of pressure drop across the filters. The N/O contact of the Air Differential Pressure Switch shall be connected to neon lamp to indicate the `filter dirty' status.

The Air Differential Pressure Switch shall be of silicone diaphragm type with calibrated adjustment knob to facilitate pressure setting suitable for operation over a wide range of temperature from -20° C to 85° C. The maximum operating pressure shall be 50 m bar.