Electric actuators in 2026 are sized on four independent axes — peak thrust or torque in newton-metres, stroke speed in mm/s or rpm, duty class (ON-time %), and fieldbus — and a wrong call on any one axis invalidates the other three, so the engineering rule of thumb is to lock the force class first and rebuild the data sheet around it.
Buyers who skip the force-versus-speed trade-off end up over-sizing the gearbox to chase a stroke time the motor cannot actually deliver at full load; the working envelope below — force / speed / duty / bus — comes from publicly released OEM selection sheets and is the same input grid the free Electric Actuator Selection Software packages listed on 3h3.com and ZOL use to short-list candidate models [S1][S3].
Define the duty window before opening any catalog
IEC 60034-1 S1-S10 duty classes (S2 short-time, S3 intermittent, S4-S9 cyclic) bind a motor to a permitted ON-time at a given ambient, and a 2026-vintage OEM datasheet typically publishes thrust curves for S2-15 min and S4-25% / S4-50% as separate lines [S4]. A valve that cycles every 4 minutes in a HVAC heat-meter station is S4-25%; a damper that strokes on every burner trip in a power plant is S4-50% to S5 territory and demands a brake-rated gearhead.
The thermal equivalent rule: continuous current on a brushless DC actuator rated S2-15 min will trip the thermistor in roughly 6-8 minutes at full load, so cyclic duty gates the motor frame even when the peak force is well within catalogue limits [S4]. Compared with a pneumatic cylinder sized purely on bore and stroke, an electric actuator adds a thermal column that buyers must fill in first.
Force class: how to anchor a realistic peak-thrust number
Peak thrust for a linear electric actuator is anchored to the valve's required seating force — typically 1.3× to 1.5× the calculated dynamic thrust for resilient-seated butterfly or ball valves, and 1.5× to 2.0× for metal-seated globe bodies because of the higher breakaway at cold-fluid startup. A 4-inch Class 150 metal-seated ball will commonly demand 8-12 kN seating, putting it into the 10 kN class of rack-and-pinion electric actuators from major OEMs [S4].
For modulating service the same package is de-rated by roughly 20-30% because the actuator rarely reaches seating force during proportional control, which is why the same 10 kN-class frame can modulate a 6-inch resilient-seated butterfly but only switch a 3-inch metal-seated ball. Treat the crossed-roller bearing guidance assembly as a separate spare-parts line: once the thrust exceeds 5 kN continuous, the crossed-roller becomes the wear item, not the brushless motor.
Three topologies versus valve geometry
Part-turn electric actuators (0-90° or 0-180°) drive butterfly, ball, and plug valves; linear actuators drive globe, diaphragm, and slurry pinch valves; multi-turn units drive rising-stem gate and globe valves through ISO 5210 mounting flanges. The selection grid below is the working baseline for the free Electric Actuator Selection Software packages released for the SMC and MC electric-cylinder catalogues [S1][S3].
Comparison on four criteria: (1) Valve fit: part-turn wins for 0-90° bodies, multi-turn for rising-stem, linear for sliding-stem; (2) Peak force envelope: linear units reach 50 kN routinely, multi-turn 25 kN·m torque, part-turn typically 5 kN·m; (3) Stroke speed: linear 20-200 mm/s, multi-turn 12-60 rpm, part-turn 5-30 s/90°; (4) Failure-mode default: most modern frames default to fail-closed via spring-return capacitor, but the spring pack is the single biggest price adder, so specify fail-safe only where the process demands it. Most plant retrofits land on linear electrics for modulating globe duty and on part-turn for on-off ball duty.
Bus protocol and the HART-versus-digital split
Specifying HART on a PROFIBUS-PA segment is a common spec error, since the two protocols are not electrically compatible — HART is FSK modulated onto a 4-20 mA loop, while PA is a digital bus with bus-powered field devices on a single twisted pair.
For a unit that also modulates, the diagnostic register set matters more than the protocol: a 2026-spec actuator should publish torque profile, number of strokes, motor temperature, and bus-health counters on register 0x01-0x0F at minimum, so that the asset-management layer can trend valve friction without a shutdown. Buyers who can lock the asset-management tag list at RFQ save roughly one commissioning day per loop on brownfield hookups.
Who should NOT pick a standard part-turn electric
A standard part-turn electric actuator is the wrong call when the seat leakage class is higher than Class VI on a metal-to-metal valve, when the ambient exceeds 60 °C without a derating curve, when the service is dirty slurry above 5% solids by mass, or when the stroke must be faster than 3 seconds at full torque. In those duty windows the spec should drop to a hydraulic actuator baseline or a pneumatic with a positioner — an electric frame will simply not survive the cycling or the heat. [S1]
Conversely, picking an electric actuator for a once-a-day fire-test isolation is over-engineered: a manual gear with an electric actuator for emergency-trip is the correct mix, since the manual gearbox can be hand-operated if the electronics fail. The same rule applies to small HVAC heat-meter actuators at DN15-DN25 — the cheap electro-thermal heads covered in the Sogou Baike entry on 电热执行器 cover that duty for a fraction of the cost of a brushless modulating frame [S4].
2026 sourcing signals: free selectors and verification paths
The free Electric Actuator Selection Software packages indexed on 3h3.com (v2.0, 23.6 MB, Windows 7/10/All, published 2020-10-22) and on ZOL (25 MB, Win7-Win10, 8.0/10 user score, updated 2023-04-07) both present a multi-language input grid covering force, stroke, speed, and duty for MC and SMC electric-cylinder catalogues, and remain the most direct way to validate an OEM shortlist without logging into a vendor portal [S1][S3].
For buyers cross-checking a quote, three trackable signals to capture this quarter are: (1) ask the OEM for the S2-15 min and S4-25% thrust curves on the same graph — a 2026 datasheet that only shows S2 is hiding the modulation envelope; (2) confirm the bus gateway supports both HART and PROFINET, not just one, since the brownfield migration in 2026-2027 is staggered; (3) request the electric ball valve assembly's tested cycle count under the actual fluid, since catalog cycle ratings are dry-bench numbers and water-service cycles can be 30-50% lower in abrasive duty.
For related coverage, see Electric Actuator Selection: Force, Speed, Duty and Bus.