An electric valve actuator opens, closes or positions a valve using electrical power and a control command. It can form part of a water, irrigation or process-control system, but the actuator must match the valve and the intended operating duty.
This guide explains actuator movement, on/off and modulating control, operating effort and mechanical fit before turning those principles into a selection checklist.
On/Off and Modulating Control
An on/off actuator moves a valve between its end positions. A modulating arrangement positions the valve between those limits in response to a control demand. The distinction is about the operating task, not merely the actuator’s size.
Positioning requires a compatible command and feedback arrangement. A signal saying that an end position has been reached is different from a continuous indication of position. Establish which information the process actually needs before choosing the controller interface.
Torque Is Not Valve Size
Nominal valve size describes a connection dimension, while torque describes the turning effort required to operate it. Valve design, process conditions and the movement being assessed affect the requirement. This is why the valve manufacturer’s operating data matters more than choosing an actuator from pipe size.
The actuator also needs the correct movement and mechanical connection. A shaft that appears to fit does not establish the required travel, mounting or load suitability. Power-failure behaviour is a further requirement: the process determines the desired position, and the exact arrangement must provide it under documented conditions.
Example: Same Valve Size, Different Requirement
Two valves with the same nominal size may need different operating torque because their designs and process conditions differ. Ask for the valve manufacturer’s requirement rather than choosing an actuator from pipe size. Then check the shaft connection, travel and control arrangement against that requirement.
What Does a Valve Actuator Do?
The actuator provides the movement needed to operate the valve. Depending on the valve design, this may be part-turn rotation, multiple turns or linear movement. The required travel and mechanical connection must be established before an actuator is selected.
Check the supply scope too. An actuator listing does not necessarily include the valve, mounting bracket or coupling.
Start With the Valve Details
For a replacement, send the complete valve and actuator model numbers, along with clear photographs of their labels and mounting arrangement. For a new installation, a valve datasheet and project specification are useful starting points.
- Valve manufacturer, model, type and size.
- Required movement and travel.
- Mounting dimensions, shaft connection and any bracket or coupling.
- Fluid, operating temperature and pressure where relevant.
A similar-looking actuator or matching shaft size alone does not establish compatibility. Mechanical fit, operating requirements and controls all need to agree.
Torque and Thrust: Use the Valve Requirement
Rotary applications are commonly specified by torque, while linear applications may require a thrust specification. Obtain the requirement from the valve manufacturer or project engineer, including the applicable operating conditions.
The force needed to start moving a valve can differ from the force needed while it is moving. Do not select an actuator from valve size alone or assume that any higher torque rating is acceptable. Required margins and the valve’s mechanical limits need assessment.
Confirm the Electrical Supply and Control
Record the available supply voltage and whether it is AC or DC. Confirm the actuator’s exact supply requirements separately from its command and feedback signals.
An on/off application needs the valve to move between its end positions. A modulating application requires intermediate positioning. Do not assume that an actuator intended for on/off operation accepts a 4–20 mA signal or can provide the required positioning performance.
If the actuator connects to a PLC or another controller, share the controller details, required command signal and feedback requirements. End-position indication and continuous position feedback are different requirements; check the exact model documentation.
What Should Happen When Power Fails?
Establish the required response to loss of power or loss of the control signal. Depending on the exact actuator and arrangement, the requirement may be to close, open or remain in position. The appropriate response depends on the process.
The T.Crystal catalogue example above is listed with a KT32S fail-safe-close arrangement. That description applies to the listed model and must not be extended to every electric actuator. Confirm the operating sequence and documented conditions for the exact unit before relying on it.
A fail-safe description does not by itself establish suitability for an emergency shutdown or another safety-related function. Those requirements need qualified assessment.
Check the Environment and Operating Duty
Tell us whether the actuator will be indoors, outdoors, exposed to washdown, chemicals, salt, dust or unusual temperatures. Include the expected operating frequency and any required opening or closing time.
An IP rating addresses ingress protection; it does not establish explosion protection, chemical compatibility or hygienic suitability. If the project specifies a hazardous area, provide the classification and required equipment approvals for assessment.
A Practical Planning Checklist
- Whether this is a replacement, new installation or upgrade.
- Complete valve and existing actuator model numbers, with label photographs.
- Valve movement, travel and required torque or thrust specification.
- Mounting and shaft details, drawings or photographs.
- Available supply and required command and feedback signals.
- Required response to power or signal failure.
- Operating duty, environment and mandatory project requirements.
- Quantity, delivery destination and required date.
You can send photographs, drawings and datasheets instead of typing out every specification. If you are unsure where to start, send the existing equipment labels and explain what the valve needs to do.
Technical Note: This guide provides general selection information. Final compatibility, process safety and compliance depend on the exact valve, actuator, control arrangement and project specification. Installation, programming and commissioning are included only where expressly quoted.
Relevant Catalogue Examples
For an enquiry, email info@softcoregroup.co.za.
Technical Resources
Visit our Technical Resources & Manuals page for documents and guidance on requesting information for your exact model. Check the relevant product listing for its supplied control diagram.