For Part 2 of our glossary of terminology used in the valve industry, we’re covering the vast array of terms related to the general topic of actuators and closure controls. We hope you find this helpful!
4-20A Signal – Standard analog control signal for valve actuators and sensors.
Actuator Sizing Torque (AST) - The minimum required shaft torque (MRST) multiplied by a safety factor.
Battery Back-up – An auxiliary power system designed to provide emergency electrical power to an actuator in the event of a primary power failure.
Bevel Gear – A gear mechanism used to change the direction of drive force; often used in manual valve actuators.
Breakaway Torque – See Unseating Torque
Chain Lever - A mechanical lever or bar, attached directly to the valve stem, with a chain attached to each end of the bar, used to open and close the valve. The chain allows a person to operate the lever at large distance below the valve
Chain Wheel – A wheel operated by a hanging chain to actuate valves located at a height.
Closed Limit – The predetermined mechanical or electrical stopping point at which the actuator ceases motion when the valve reaches its fully closed position.
Cylinder Operator (Actuator) – A valve actuator powered by hydraulic or pneumatic cylinder(s).
Dampener – A device (typically a hydraulic or pneumatic cylinder) that resists the opening or closing of a valve.
Dampening Cylinder – A hydraulic or pneumatic device used to slow down or control the motion of a valve, gate, or actuator to prevent shock, vibration, or abrupt movement.
Dashpot – A device that resists the valve actuation by use of a dampener. Typically, a hydraulic cylinder used to resist the closing of a check valve.
Deadman Handle – A handle that returns the valve to a safe position when released.
Declutch – A mechanical feature that allows manual operation of the valve by disengaging (declutching) the actuator’s drive mechanism from the valve stem or gear train.
Device Net – An industrial communication protocol used to connect control devices such as sensors, actuators, and programmable logic controllers (PLCs) within a network.
De-Zincification Resistant (DZR) – Material property for brass valves in potable water systems.
Diaphragm Operator (Actuator) – An actuator that uses a diaphragm, typically driven by air pressure, to move the valve stem.
Drive Bushing – an adapter that connects the actuator output to the valve stem.
Ethernet IP – An industrial automation protocol that uses standard Ethernet technology to connect industrial devices like PLCs, sensors, actuators, and drives for real-time control and data exchange.
Electro-hydraulic Actuator - A valve actuator that combines electrical control with hydraulic power to operate valves that typically require high force.
EMO – Electric Motor Operator; an actuator powered by an electric motor.
Explosion Proof – A electrical enclosure designed to contain any internal explosion and prevent it from igniting a hazardous atmosphere outside the enclosure.
Extension Stem – The rod that connects the actuator or handwheel to the valve closure element.
Fail Close/Open/In Place – Describes the default position a valve returns to upon loss of power or signal.
Fail Safe – A valve or actuator design that moves to a predetermined safe position upon loss of power.
Foundation Fieldbus – A digital, bi-directional communication protocol used in process and manufacturing automation to replace traditional 4-20 mA analog signals.
Gearbox – a mechanical device containing gears that transfers rotating power from a source to another component, typically used to change the speed and torque of the rotating power.
Gear Reducer – a mechanical device containing gears that increases or reduces rotating speed from a source to another component.
Hand Lever - A mechanical lever or bar used to open and close a valve.
HART Protocol – A communication protocol used for digital smart valve controllers.
Hold Open Device – A device used to hold a check valve open.
HWO – Hand Wheel Operator; a valve operated manually by a wheel.
Hydraulic Operator (Actuator) – Uses pressurized fluid for actuation.
Hydraulic Power Unit (HPU) – A self-contained system that generates and supplies pressurized hydraulic fluid to power hydraulic actuators or control valves. It typically includes a reservoir, pump, motor, filters, and control elements.
Indicator Post – Displays the open/closed status of buried OS&Y gate valves.
Indicator Plate – a plate on an actuator providing indication of the actuator's position in relation to fully open or closed.
Intrinsically Safe – a design approach for electrical equipment that ensures the equipment cannot release enough electrical or thermal energy to ignite an explosive atmosphere.
IP Rating – (Ingress Protection rating) is a standardized system that classifies the degree of protection an enclosure provides against the intrusion of foreign objects and moisture. It's a two-digit code, with the first number indicating protection against solids and the second against liquids.
I/P Converter – Converts current signal (4–20 mA) to pneumatic (3–15 psi) for actuator control.
Key Stop – A device to limit valve travel or indicate fully open/closed positions.
Lever Actuator – A mechanical lever or bar, attached directly to the valve stem, used to open and close a valve.
Limit Switch – Indicates the valve's open or closed position.
Limit Torque Switch – See Torque Limit Switch
Local Controls – see Remote Hand Station
Local Hand Station – see Remote Hand Station
Locking Device – A mechanism that allows a valve to be locked in position.
Manual Gear Operator (Actuator) – A gear mechanism for manually operating a valve with reduced torque effort.
Manual Override - A mechanical feature that allows manual operation of the valve by disengaging (declutching) the actuator’s drive mechanism from the valve stem or gear train.
Maximum Allowable Stem Torque (MAST) - The greatest torque to which a valve stem can be subjected to without mechanical failure.
Mechanical Stops – A mechanism used to adjust and limit the open and closed position of a valve.
Minimum Required Shaft Torque (MRST) - The operating torque values through the entire valve opening and closing strokes.
Miter Gear – A gear set used to transmit motion at a 90° angle.
Modbus – a standard communication protocol used to establish communication between industrial electronic devices, typically over serial lines or Ethernet.
Modbus RTU (Remote Terminal Unit) – a binary-encoded version of the Modbus protocol, typically used over RS-485 or RS-232 serial communication lines.
Modbus TCP/IP (Transmission Control Protocol/Internet Protocol) – A variation of the Modbus protocol that enables communication between industrial automation devices over an Ethernet network using the TCP/IP protocol.
Modulating Service – Valve use in applications requiring precise control of flow.
Multi-Turn Valve – Requires multiple rotations to operate the valve.
NEMA – A rating system established by the National Electrical Manufacturers Association (NEMA) to classify the level of protection that an electrical enclosure provides against environmental factors like dust, water, and corrosion.
Non-Intrusive – Enclosures in industrial settings that protect sensitive equipment from harsh conditions (dust, water, chemicals, etc.) without requiring physical penetration into the protected space or device.
Nut – See Operating Nut
NRS – Non-Rising Stem; a valve stem that does not extend when the valve is operated.
Open/Close Service – Valve service limited to full open or full closed operation.
Open limit – The predetermined mechanical or electrical stopping point at which the actuator ceases motion when the valve reaches its fully open position.
Operator – A mechanical device that moves or controls a mechanism or system; in valves, it opens or closes the valve via electric, pneumatic, or hydraulic power.
Operating Nut – The drive nut that permits opening and closing valves using a wrench.
Operating Torque – The torque needed to operate the valve under pressure.
OS&Y – Outside Screw and Yoke; a valve with an externally rising stem for position indication.
Pneumatic Booster – Device that increases air pressure for faster actuator response.
Pneumatic Operator (Actuator) – Uses compressed air to operate the valve.
Positioner - A device that controls the position of a valve, by adjusting the actuators’ air pressure, in response to a signal from a controller.
Position Feedback – Sends information about valve position to a control system.
Position Indicator – A device that visually shows the position of a valve, indicating whether it's open, closed, or in an intermediate position.
Profibus – (Process Field Bus) A standardized fieldbus communication protocol used in industrial automation.
Proximity Switch – A non-contact sensor that detects the presence or absence of an object without physical contact.
Rack and Pinion – (Rack and Pinion Gearbox) A type of linear actuator that converts rotational motion (motor, handwheel, chainwheel, or nut) into linear motion which drives the valve stem.
Remote Control Station (RCS) – A duplicate actuator interface that allows users to operate an actuator remotely, either via wired or wireless connection.
Remote Hand Station – An additional actuator interface that allows users to operate an actuator remotely, typically with very limited functions and via a wired connection.
Rim Pull – The amount of force required at the handwheel rim to operate a valve.
Rising Stem – A valve stem that moves up visibly when the valve is opened.
SCADA – (Supervisory Control and Data Acquisition) - A system used to monitor and control industrial processes, equipment, and infrastructure. It encompasses hardware and software components that allow operators to gather data, visualize it, and make control decisions remotely or locally.
Scotch Yolk Operator (Actuator) – An actuator that converts rotary motion to linear using a yoke mechanism. Also known as a Traveling Nut Actuator.
Seating Torque – The torque required to seat (close) the valve fully.
Single Acting Actuator – see Spring Return Actuator
Smart Positioner – A digital device that adjusts valve position and provides diagnostics.
Speed Controls – Devices or settings used to regulate the speed of valve movement, often to prevent water hammer or to allow smooth operation in hydraulic or electric valve actuators. They may include needle valves, flow restrictors, or electronic controllers.
Spring Return Actuator – An actuator that uses a spring to automatically return a valve to a pre-set "fail-safe" position (either fully open or fully closed) when power or air pressure is lost.
Square Operating Nut – A square-shaped nut used for manual operation with a wrench.
Stem – See Extension Stem or Valve Stem
Stem Guide – A mechanical arm or ring providing support for valve extension stems.
Stroke Time – The time it takes for the valve to open or close fully.
T-Handle – Industry standard extended wrench used to open and close a valve by mating the T shaped handle’s square receptacle to the square operating nut on the input shaft of a valve.
Thermal Expansion – Stress or movement due to temperature changes in the valve or media.
Throttling – Regulating flow by partially opening or closing a valve.
Throttling Service – Application in which a valve controls flow at a partially open position, rather than a simple on/off service.
Torque – A twisting force that causes rotation.
Torque Limit Switch – Prevents damage by cutting power at end of valve travel or high torque.
Torque Rating – Maximum torque a valve or actuator is rated to withstand.
Torque Seating – Uses actuator torque to achieve valve shutoff.
Torque Tube – The rotating drive tube extending a valve stem to an elevated position, typically used with a floorstand.
Travel Stop – Prevents over-rotation in manual or automated valves.
Traveling Nut Operator (Actuator) – An actuator that converts rotary motion to linear using a yoke mechanism. Also known as a Scotch Yolk Actuator.
Unseating Torque – The torque required to start valve movement from the closed position.
Valve Box – A enclosure used to protect a valve, an actuator, or drive nut from damage or contamination. Typically, it includes a heavy-duty lid to protect the drive nut from vehicle traffic.
Valve box Extension – Stackable or telescoping tubing that extends a valve box from ground level to an underground valve actuator.
Vane Operator (Actuator) – A rotary actuator using air pressure on a vane to operate a valve.
Water Cylinder Operator (Actuator) – A type of actuator powered by water pressure, converting hydraulic energy into mechanical motion to operate valves. Common in systems where water is readily available as a motive force and pneumatic or electric actuation is not ideal.
Worm Gear – A gear mechanism used to reduce speed and increase torque for valve actuation.
Yoke – The structure that supports the valve actuator and guides the stem movement.
