Multi-Turn Electric Actuators: Selection and Configuration

ted wang
Jun 4
2 min read

Where Multi-Turn Actuators Are Used

Multi-turn electric actuators are used to operate gate valves, globe valves, rising stem ball valves, and other linear-stem or multi-turn valves where a quarter-turn actuator is not suitable. They are preferred in applications where pneumatic or hydraulic supply is unavailable, where precise positioning is required, or where remote monitoring and control via fieldbus communication is desired.

Key Performance Parameters

Thrust output (kN): for linear stem valves, the thrust required to unseat and travel the valve
Torque output (Nm): for rotary stem valves operated with multi-turn drive
Number of turns: full travel stroke in revolutions, matched to valve stem lead and travel
Operating speed: adjustable, typically 4 to 200 seconds for full stroke
Duty cycle: S2 (short-time duty) or S4 (intermittent duty) rating depending on usage frequency

Torque Limiting and Position Control

Electric actuators include torque-limiting switches that cut off power if the required torque exceeds the preset limit, protecting the valve from damage. Position switches define the full-open and full-close positions and stop actuator travel. Modulating actuators use an analog position transmitter (4-20 mA) and integral positioner for proportional control. Reversing starters or variable frequency drives control direction and speed.

Communication and Smart Features

HART protocol: superimposed digital signal on 4-20 mA loop for diagnostics and configuration
Foundation Fieldbus, PROFIBUS, or Modbus: digital communication for smart plant integration
Non-intrusive setting: configure torque and position limits without opening the actuator enclosure
Data logging: stores operating history, torque profiles, and alarm events
Partial stroke testing: built-in PST function for ESD valve testing compliance

Environmental and Installation Considerations

Electric actuators must match the installation environment: IP65 or IP67 rating for outdoor use, ATEX or IECEx certification for hazardous areas. Motor winding insulation class F or H is required for high-temperature environments. Heaters and thermostats prevent condensation inside the actuator enclosure. Cable entries must be correctly sealed for the IP rating with appropriate glands and conduit fittings.