Actuators
According to ISO 22153, a part-turn actuators is an actuator which transmits torque to the valve for less than one revolution, and does not need to be capable of withstanding operational thrust.
Part-turn valves – butterfly valves or ball valves – are often designed in multi-turn version. SQ part-turn actuators are equipped with internal end stops to allow precise approaching of end positions during handwheel operation.
Class A: OPEN-CLOSE duty. The actuator is required to operate the valve across its entire travel from the fully open position to the fully closed position or vice versa.
Class B: Inching, positioning or positioning duty. The actuator is required to occasionally operate the valve to any position (fully open, intermediate and fully closed).
Class C: Modulation or modulating duty. The actuator is required to frequently operate the valve to any position between fully open and fully closed.
Class D: Continuous modulating. The actuator is required to continuously operate the valve to any position between fully open and fully closed.
