Valve actuator selection: force, stroke and signal
An actuator can render even a correctly selected valve useless. Compatibility is checked under six headings.
Valve actuator selection rests on six values: required force (N) or torque (Nm), stroke (mm) or rotation angle, permissible close-off pressure (Δp), running time, supply voltage (AC/DC 24 V or AC 230 V) and control signal (on-off, 3-point or DC 0–10 V / 4–20 mA). Insufficient force means the valve will not close tightly at high differential pressure, causing continuous leakage; a stroke mismatch means it will not fully open.
Close-off pressure is the most overlooked value
The highest differential pressure that can appear across a valve while the pump runs and other circuits are closed is what the actuator must overcome. This can be far higher than the design Δp. Insufficient force is the most common cause of the complaint "the valve is closed but the circuit is still heating".
Signal type and controller compatibility
An on-off actuator moves between two positions; a 3-point actuator takes intermediate positions via open/close relay outputs; a modulating actuator can reach any intermediate position with a DC 0–10 V or 4–20 mA signal. If the control strategy requires modulation the actuator must be modulating too — otherwise the controller's resolution is wasted.
Running time and system response
A very fast actuator paired with a slow-responding coil leads to overcorrection and hunting. A very slow actuator cannot keep up with rapid load changes. Choosing running time for the application comes before tuning control parameters.
Frequently asked
Can a different actuator be fitted to the same valve?
Yes, if the mounting interface, stroke and required force match. However, in combinations not listed as compatible by the manufacturer the close-off pressure guarantee no longer applies.
When is a spring-return actuator required?
When the valve must move to a defined position on power failure: frost protection, safety shut-off or process-safety applications.
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