Model DFS-221-112 Air Pressure Sensing Switch is a 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. Model DFS-221-112 can be used to sense positive, negative, or differential air pressure. The plated housing contains a diaphragm and a snap-acting SPDT switch. The DFS- 221-112 is equipped with convenient dual- barbed sample line connectors located on each side of the diaphragm. The dual-barbed connectors accept 3⁄16″ or 1⁄4″ ID flexible tubing. The electrical connection consists of 1⁄4″ 90o quick connect spade terminals. The SPDT snap action switch operates on pressure rise of 0.05 ± 0.02″ w.c. For additional application and technical information, please contact the sales office.