Model DFS–221 is an airflow proving switch designed for duct heater, oven, and other HVAC or Energy Management applications where an open-mounted, nonadjustable switch is desirable. It is especially suitable for surface-mounting in areas where internal access is limited. It can be used to sense positive, negative, or differential air pressure.

The DFS–221 is equipped with two convenient sample line connectors (1⁄4″ OD slip-on fittings) that accept flexible tubing.

The plated housing contains a diaphragm and a snap-acting SPDT switch. The sample line connections located on each side of the diaphragm accept flexible tubing. The electrical connection consists of male 1⁄4″ quick connect terminals.

The SPDT snap action switch operates on pressure rise of 0.05″w.c., ± 0.02″ w.c.