The Cleveland Controls Model DFS-221 Fixed Differential Pressure Switch is an airflow proving switch designed for duct heater, oven, and other HVAC and energy management applications. The unit senses positive, negative, or differential pressure with SPDT switch actuation on pressure rise at 0.05 WC, ±0.02 WC. The model DFS-221 is equipped with two barbed sample line connections for use with ID flexible tubing. Electrical connections are made via male quick connect terminals for easy installation.