Replaceable dwyer air flow switch Description The duct air flow switch provides feedback of air flow in HVAC duct work. It can be directly connected to the control system as a feedback point or interlocked to prevent operation of heating and cooling equipment when there is no air flow. The stainless steel paddle resists corrosion. An adjustable spring tension screw allows setting the air flow trip point from 200 to 1800 FPM (1 to 9.2 m/sec). The paddle can be trimmed down for