Speed of Power Actuators:

Plant safety considerations dictate valve speeds for certain safety-related valves. Whereas a system has to be extremely quickly isolated or opened, extremely fast valve actuation is needed. Whereas the opening of a valve results in injection of associative cold water to a hot system and slower opening is essential to minimize thermal shock. The engineering design selects the actuator for safetyrelated valves based upon speed and power needs and availability of energy to the actuator.

In common, fastest actuation is given through pneumatic, hydraulic, and solenoid actuators. Therefore, solenoids are not practical for huge valves since their size and power needs would be excessive. In addition, hydraulic and pneumatic actuators need a system for giving hydraulic or pneumatic energy. A speed of actuation in either case could be set through installing approx sized orifices within the hydraulic or pneumatic lines. In many cases, the valve is closed through spring pressure, that is opposed through hydraulic or pneumatic pressure to remain the valve open.

Electrical motors give associatively fast actuation. Original valve speed is set through the combination of motor speed and gear ratio. This combination could be selected to gives full valve travel inside a range from about two seconds to various seconds.