Custom Actuation Solutions Since 1973

Actuation Glossary

 In a continuing effort to deliver the best customer service possible and provide you with quick turnaround times on quotes, we want to ensure that you are familiar with actuation terminology. This will enable our sales team to rapidly identify your project needs and provide you with an accurate quote for your project. The following list of valve automation terms may help us communicate and better serve your needs.


On-Off Service When the valve is being used to start or stop flow by being cycled to the full open or full closed position.

Modulating Service When the valve is being used to throttle or regulate the rate of flow by being positioned at varying positions between open and closed.

Media The material flowing through the valve.

Maximum Shut-Off Pressure The pressure of the media flowing into the valve against which the valve will have to close.

Service Temperature The maximum and minimum temperature of the media.

Supply Pressure The plant air supply pressure available to operate a pneumatic actuator.

Stem Torque The force required at the valve stem to open or close the valve against system pressure and service conditions. Torque is expressed in inch pounds or foot pounds.



Pneumatic Actuator An air-operated mechanical device used to open and close or modulate a valve. The actuator, which is mounted to the valve by a bracket and coupled to the stem, is designed to convert air pressure into mechanical force sufficient to operate the valve.

Double-Acting Pneumatic Actuator Any pneumatic actuator which uses air to drive the actuator output shaft in both the open and close direction. The air supply is piped to one side of a piston drive or a diaphragm while the air contained on the opposing side is exhausted.

Spring-Return Pneumatic Actuator Any pneumatic actuator which contains a single coil spring or group of coil springs to oppose the movement of a piston or diaphragm. As air moves the piston or diaphragm the spring is compressed. When the air supply is discontinued and exhausted, the spring extends and drives the piston or diaphragm in the opposite direction. This type of actuator is normally used for applications where it is necessary for the valve to move to the open or close position upon loss of air supply, whether by design or by system failure.

Fail-Open A spring return pneumatic actuator is applied to the valve such that the spring will drive the valve to the open position upon loss of air (may be termed "air-to-close").

Fail-Closed A spring return pneumatic actuator is applied to the valve such that the spring will drive the valve to the close position upon loss of air (may be termed "air-to-open").

Electric Actuator An electro-mechanical device used to open, close or modulate a valve. The actuator operates the valve using an electric motor driving a gear train. While the basic function of the electric actuator is similar to the pneumatic, there are distinct differences in the application and flexibility of the two types, and these differences should be considered to select the proper type.

Electric Fail Safe Actuator Electrically driven actuator that contains an internal spring to close the valve on loss of electricity.



NEMA Rating National Electrical Code Ratings for electrical component enclosures.

NEMA 4 Weather-proof enclosure suitable for indoor/outdoor applications to protect from windblown dust, rain or hose-directed water.

NEMA 4x Offers the same protection as Nema 4 with the addition of corrosion resistance.

NEMA 6 Enclosure that may be submerged up to six feet for 30 minutes.

NEMA 7 Enclosure for hazardous locations, must be capable of withstanding an internal explosion of gases so as not to ignite an external gas-air mixture.

Limit Switches Electrical switches which may be applied to manual or automated valves to signal that the valve cycle has been completed. When applied to manual or pneumatically actuated valves, it is most common to provide two switches in a Nema rated enclosure. Each switch is activated by an adjustable tripping device driven by the actuator or valve system. Normally one switch is adjusted to trip in the open position and one is adjusted to trip in the closed position. Optional additional switches are available to perform other functions (i.e., pump start-up or shut-down). All electric actuators have Open/Close limit switches.

Mechanical Limit Switch Any limit switch (usually plunger or lever type) that is mechanically activated by the tripping mechanism making physical contact with the switch, and is normally used for remote valve position indication.

Proximity Limit Switch A solid state switch that is electrically tripped without mechanical contact being made. This type of switch is generally used to interface with computer or microprocessor controls.

Solenoid Valve An electro-magnetically operated valve which enables electrical control of the air supply to a pneumatic actuator. Double-acting actuators require a four-way solenoid, while the spring-return actuators require a three-way solenoid to achieve the proper supply-exhaust air flow patterns.

Positioners Instrument attached to a pneumatic valve actuator, providing accurate, automatic modulating control of the valve between the open and closed positions by increasing, decreasing, and balancing the air supply to the actuator as determined by a varying input signal generated by an external instrument source. While the operation positioners may vary, the basic function will be either the pneumatic positioner, designed to receive a 3 to 15 PSI signal, or the electro-pneumatic, designed to receive a 4 to 20 milliamp signal.

Manual Over-ride Any mechanical device by which an automated valve may be manually operated. On smaller actuators, this may simply be wrench flats on the output shaft of the actuator. Larger actuators may require a more sophisticated system, such as declutchable handwheels, manual gears, jack screws, or hydraulic hand pump over-ride.


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