In compliance with ISO 5210, a multi-turn actuator is capable of withstanding thrust applied to the valve and transmits torque to the valve for at least one revolution. In general, multi-turn actuators are required to perform more than one revolution. Consequently, gate valves are often equipped with rising valve stems. They are operated on the basis of several revolutions performed by the multi-turn actuator. Therefore, the multi-turn actuator is equipped with a hollow shaft housing the gate valve stem for these applications.
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.