The Cleveland Controls AFS-460-121 is a versatile air flow switch designed to monitor positive, negative, or differential air pressure in HVAC systems and other air-handling applications. It operates in a range of 0.4 to 12 inches of water column (WCM), making it suitable for low to moderate pressure applications. https://www.partshnc.com/afs-460-121-cleveland-controls-412-wcmr-airswwaccessorys