Valve jamming and excessive operating torque are important considerations in chemical process automation. Ball valves, butterfly valves, and other quarter-turn valves may experience changes in operating resistance due to impurities, mechanical conditions, pressure variation, or changes inside the valve after extended service.
If an electric actuator is selected without considering the actual valve torque, abnormal mechanical loads may affect both the valve and the drive mechanism. For this reason, electric actuator torque sizing and over-torque protection should be evaluated together when selecting actuators for chemical processing systems.
Why Valve Size Alone Is Not Enough for Actuator Selection
Nominal valve diameter is useful as an initial reference, but it does not directly determine the required actuator torque.
According to the DCL product documentation, valves with the same type and nominal size may still have different operating torque because of manufacturing technology, valve material, process medium, site conditions, and pressure fluctuation. The documentation therefore recommends selecting the actuator according to actual torque data supplied by the valve manufacturer and applying an approximate 1.1–1.3 torque allowance factor.
For chemical-industry ball valves and butterfly valves, this torque-based sizing method provides a more useful engineering basis than selecting an actuator only by DN size.
Which Torque Parameters Should Be Checked?
A practical selection process should consider:
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normal valve operating torque;
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breakaway or starting torque;
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process pressure and medium;
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actuator rated output torque and maximum torque;
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the need for over-torque protection.
The DCL explosion-proof electric actuator range covers models from DCL-Ex05 to DCL-Ex300, with standard output torque from approximately 50 Nm to 3000 Nm. The DCL-Ex300 provides 3000 Nm standard output torque and a specified maximum torque of 3900 Nm.
This range allows actuator selection to be based on actual valve torque requirements rather than a single standard size.
How Does Over-Torque Protection Address Valve Jamming?
Chemical pipelines may carry media containing impurities or foreign material. Under certain operating conditions, this can increase valve resistance or cause a valve to become stuck.
The DCL documentation describes an optional Over-Torque Protection Function. If valve resistance causes actuator output torque to rise to a preset critical value, the torque switch can disconnect the drive circuit to reduce the risk of continued abnormal loading on the valve and actuator.
This function may therefore be considered for applications where valve jamming or unexpected torque increases are part of the operating risk assessment.
However, over-torque protection should not replace correct actuator sizing. An undersized actuator may repeatedly reach its protection threshold, while an actuator with unnecessarily high torque may impose excessive mechanical load on the valve under abnormal conditions.
Hazardous-Area Requirements Must Be Checked at the Same Time
Torque is only one part of actuator selection in a chemical plant. Hazardous-area classification can be equally important.
The DCL Explosion-Proof Electric Actuator documentation lists ATEX/IECEx protection including Ex db h IIC T4 Gb. Under the CSA system, classifications include Class I, Division 1, Groups C and D T5/T6 and Class I, Zone 1, AEx db IIC T5/T6 Gb. The explosion-proof series is specified with an IP68 enclosure and an ambient temperature range of -25°C to +55°C.
Engineers should therefore verify hazardous-area classification, certification scope, torque, enclosure protection, and ambient conditions together.
Modulating Applications Also Require Control Performance
Chemical processes that regulate flow, pressure, temperature, or liquid level may require proportional valve positioning rather than simple open/close control.
DCL Type E/GEY modulating explosion-proof actuators accept 4–20mA DC, 1–5V DC, or 2–10V DC input signals and provide 4–20mA DC position feedback. The documented basic error is no more than ±1%, while repeating error is no more than 1%.
These values provide measurable criteria when evaluating an actuator for a process-control loop.
Select the Actuator by Complete Operating Conditions
Electric actuator selection for chemical valves should move beyond the simple question of “How much torque is required?"
A more complete sequence is: actual valve torque → torque allowance → jamming risk → over-torque protection → hazardous-area classification → power and control signals → environmental conditions.
The DCL explosion-proof range combines 50–3000 Nm standard output torque, IP68 protection, optional over-torque protection, and 4–20mA modulating control options. These specifications allow selection to be based on measurable operating requirements rather than broad claims about performance or reliability.