In compliance with ISO 5211, part-turn actuators transmit torque to the valve for a rotation of one revolution or less. They do not have to be capable of withstanding axial thrust. Part-turn valves - such as butterfl y valves and 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.
OPEN-CLOSE or modulating duty
Class A: OPEN-CLOSE duty. The actuator is required to drive the valve through 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 drive the valve to any position (fully open, intermediate and fully closed).
Class C:Modulation or modulating duty. The actuator is required to frequently drive the valve to any position between fully open and fully closed.