Why is direct-acting action chosen for large-diameter valves?
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Why should positive-acting actuators be chosen for large-diameter valves?
Not necessarily! Selected according to the process requirements!
I’m not really sure if there’s such a requirement; I hope experts can provide an answer.
There’s a sentence in the instrument technician’s manual that I don’t quite understand either! So I’m seeking advice from experts.
Control valve actuators come in direct-acting and reverse-acting types, while the control mechanisms can be arranged with the spool in either a forward or reverse orientation. Different combinations of actuators and control mechanisms enable air-operated open and air-operated closed operation. Currently, the valve spools of control valves are generally installed in the normal orientation; therefore, to achieve air-operated open or air-operated closed operation, it is necessary to use actuators with a direct or reverse action. The choice between air-open and air-close for the control valve is determined to ensure the safety of the process and equipment.