How do I specify actuator runtime for different applications?

Actuator runtime — the time the actuator takes to travel from fully closed to fully open — should match the process dynamics: fast-acting processes need fast actuators, while slow thermal systems benefit from slower runtimes that prevent hunting. For VAV terminal unit dampers, 60–90 second runtimes are standard and allow the DDC controller's PID loop enough time to sense the result of a damper position change in the zone temperature. For large AHU mixing dampers (outdoor/return air), 90–150 second runtimes are typical because the mixed air temperature response is relatively slow. Steam valves require faster actuators (15–30 seconds) because steam systems react quickly to changes in valve position. Specifying an actuator that is too fast for the process will cause instability and hunting; too slow and the system cannot respond to disturbances — Belimo's sizing tools match runtime to application type automatically based on the thermal time constant of the controlled medium.