Process Controls VALVE ACTUATORSA major advantage of solenoid actuators is their quick operation. Also, they are much easier toinstall than pneumatic or hydraulic actuators. However, solenoid actuators have twodisadvantages. First, they have only two positions: fully open and fully closed. Second, theydon’t produce much force, so they usually only operate relatively small valves.ElectricMotorActuatorsElectric motor actuators vary widely in their design and applications. Some electric motoractuators are designed to operate in only two positions (fully open or fully closed). Other electricmotors can be positioned between the two positions. A typical electric motor actuator is shownin Figure 39. Its major parts include an electric motor, clutch and gear box assembly, manualhandwheel, and stem connected to a valve.Figure 39 Electric Motor ActuatorThe motor moves the stem through the gear assembly. The motor reverses its rotation to eitheropen or close the valve. The clutch and clutch lever disconnects the electric motor from the gearassembly and allows the valve to be operated manually with the handwheel.Most electric motor actuators are equipped with limit switches, torque limiters, or both. Limitswitches de-energize the electric motor when the valve has reached a specific position. TorqueRev. 0 Page 59 IC-07
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