The Cleveland Controls NS2-0306-00 is a factory-calibrated air pressure switch designed to monitor airflow and ensure safe HVAC system operation. Preset at 0.37 inches water column, it uses an internal silicone diaphragm to detect air pressure changes and activate an electrical switch when the required pressure is reached. Commonly used in gas furnaces, boilers, and heating equipment,... https://www.partshnc.com/ns2-0306-00-cleveland-controls-air-pressure-switch