Valve actuator motors: torque to unseat, not power to run

12.5 Nmneeded at the motor to unseat

19 Nmmotor starting torque

0.75 kWmotor selected

The duty

A valve needs 300 Nm at the actuator output to unseat and 150 Nm while travelling. The actuator uses a 60:1 worm gear with about 40 % efficiency at start and 55 % running. Output speed is 24 rpm.

Torque at motor to unseat 300 ÷ (60 × 0.40) = 12.5 Nm Torque at motor running 150 ÷ (60 × 0.55) = 4.5 Nm Running power 4.5 × 1,440 ÷ 9,550 = 0.69 kW

The motor

EM2-80-4-0.75: M_N 5.0 Nm, starting torque 3.8 × M_N = 19 Nm, breakdown 3.8 × M_N. It unseats the valve with a 1.5 × margin and runs at about 90 % of rated torque.

Short-time duty

Valve strokes last seconds to minutes, so actuator motors are rated for S2 (short-time) or S3 (intermittent) duty rather than continuous S1. EMPD designs actuator motors for this duty with high starting torque, in compact special-mounting frames from 63 to 100, delivering 2 to 70 Nm.

Protection

Thermostats in the winding protect against repeated strokes in quick succession.
The actuator's torque switches, not the motor, limit the seating force.

Application study: an engineering example worked by EMPD with catalogue data. Your application is confirmed by our engineers before quotation. Send us your duty.

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