What is actuator close-off pressure and why is it critical?

Close-off pressure is the maximum differential pressure against which an actuator can fully close its damper or valve and hold it sealed — exceeding this rating causes the damper to blow open or the valve to leak. For control valves, the close-off rating must exceed the maximum pump deadhead pressure at the valve location (typically 50–150 PSI for medium-rise hydronic systems), while dampers must accommodate maximum fan static pressure plus stack effect or wind pressure (up to 8–10 in. w.g. in high-rise pressurization applications). Always select an actuator providing at least 1.5× the calculated close-off requirement using manufacturer close-off tables from Belimo, Honeywell, or Siemens that map actuator torque to damper area or valve seat diameter.