The air pressure switch is a general purpose airflow proving switch designed for HVAC and Energy Management applications. It may be used to sense positive, negative, or differential air pressure. The housing contains a diaphragm, a calibration knob and a snap-acting SPDT switch. The 2 sample connections located on each side of the diaphragm accept 6.35mm(0.25")OD tubing An enclosure cover guards against accidental contact with the live switch terminal screws and the set point adjusting knob.The enclosure cover will accept a 12.7 mm (0.5") conduit connection or M20 connection.An enclosure cover guards against accidental contact with the live switch terminal screws and the set point adjusting knob.