Reference
Electric actuator glossary
Plain-language definitions of the terms used across FFC product, application, and flow-media pages — from torque and duty cycle to fieldbus protocols and hazardous-area certification.
Actuation & motion
- Electric actuator
- An electromechanical drive that opens, closes, or positions a valve using an electric motor and gear train instead of pneumatic or hydraulic power. It converts an electrical control signal into mechanical torque or thrust at the valve stem.
- Part-turn actuator
- An actuator that rotates the valve through a limited arc, typically 90°, to drive quarter-turn valves such as ball, butterfly, and plug valves. Output is rated in torque (N·m).
- Multi-turn actuator
- An actuator that delivers multiple output rotations to drive rising-stem valves such as gate and globe valves, or other multi-turn devices. It is rated in torque and may also be characterised by thrust and stem acceptance.
- Linear actuatorthrust
- An actuator that produces straight-line motion (thrust) rather than rotation, used for linear-stem valves and dampers. A rotary actuator can also drive a linear stem through a thrust unit or linear adaptor.
- Handwheel override
- A manual mechanism that lets an operator position the valve by hand when power is unavailable. A declutching design engages the handwheel only when needed so the motor cannot back-drive it during normal operation.
Sizing & duty
- TorqueN·m
- The rotational force an actuator applies to the valve, expressed in newton-metres (N·m). Sizing compares the actuator's rated output torque against the valve's required torque across the operating cycle, including break-to-open and seating.
- Torque safety factor
- The margin applied between the valve's required torque and the actuator's rated torque to allow for wear, friction, process variation, and voltage drop. The appropriate margin depends on the valve type, service, and project specification.
- Duty cycle
- How much of a period an actuator can run versus rest without overheating. On/off (isolating) duty is described by starts per hour and run time; modulating duty is described by class (for example S4) and a higher permitted starts-per-hour rating.
- Modulating service
- Control mode in which the actuator continuously repositions the valve to follow a setpoint (for example a 4–20 mA demand), as opposed to on/off service that only fully opens or closes. Modulating service demands higher duty class and positioning resolution.
- Isolating (on/off) service
- Control mode in which the valve is driven only fully open or fully closed. It places lower thermal and resolution demands on the actuator than modulating service.
Protection & safety
- IP ratingIEC 60529
- Ingress Protection code (IEC 60529) describing enclosure sealing against solids and water, written as two digits — for example IP67 means dust-tight and protected against temporary immersion. IP68 adds continuous immersion to a stated depth and duration.
- Explosion-proof / flameproofEx d
- A type of protection for hazardous (potentially explosive) atmospheres in which the enclosure contains any internal ignition and prevents it from propagating outside. Flameproof 'Ex d' is one of several protection concepts defined by IEC 60079.
- Emergency shutdownESD
- A safety function that drives the valve to a defined fail position on a trip signal or loss of power. It can be implemented with stored energy such as a spring return or a battery/capacitor back-up that completes the last command.
- Fail-safe position
- The predetermined state the valve assumes on loss of power or signal — fail-open, fail-closed, or fail-in-place (stay put). The required fail action is set by the process safety design, not by the actuator alone.
- Safety Integrity LevelSIL
- A measure (IEC 61508 / IEC 61511) of the risk reduction provided by a safety instrumented function, from SIL 1 to SIL 4. An actuator used in a safety function is selected to suit the target SIL of the loop it serves.
Control & communication
- ModbusRTU / TCP
- A widely used industrial communication protocol. Modbus RTU runs over serial RS-485 networks; Modbus TCP runs over Ethernet. Both let a control system read status and send commands to field devices such as actuators.
- PROFIBUSDP
- A fieldbus standard common in process and factory automation. PROFIBUS DP exchanges cyclic process data between a controller and distributed devices over an RS-485 segment.
- FOUNDATION FieldbusFF
- A digital, two-way fieldbus protocol used for process instrumentation, supporting device-level diagnostics and, in some topologies, distributed control function blocks.
- HART
- A protocol that superimposes a digital signal on the conventional 4–20 mA analogue current loop, allowing digital configuration and diagnostics while preserving the analogue control signal.
- Position feedback4–20 mA
- A signal reported back to the control system indicating actual valve position, commonly a 4–20 mA analogue output or a digital value over a fieldbus. It lets the controller confirm and trim position in modulating service.
Standards & compliance
- ATEX
- The European Union framework governing equipment for use in potentially explosive atmospheres. ATEX certification classifies equipment by zone, gas/dust group, and temperature class for safe deployment in hazardous areas.
- IECEx
- An international certification scheme for equipment used in explosive atmospheres, based on the IEC 60079 series. IECEx certificates support acceptance across many countries that recognise the scheme.
- ISO 5211
- The international standard defining the mounting interface (flange and drive coupling dimensions) between part-turn actuators and valves, enabling interchangeability between compliant actuators and valves.
- Enclosure / area classification
- The categorisation of an installation area by the likelihood of an explosive atmosphere (for example Zone 1 or Zone 2 for gases). Equipment is selected with a protection concept and certification matching the area classification.
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