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Hydraulic and Pneumatic Knowledge
Fluid Power Equipment
Electric motor actuators vary widely in their design and
applications. Some electric motor actuators are designed to operate in only two
positions (fully open or fully closed). Other electric motors can be positioned
between the two positions. A typical electric motor actuator is shown below. Its
major parts include an electric motor, clutch and gear box assembly, manual hand
wheel, and stem connected to a valve.
The motor moves the stem through the gear assembly. The motor
reverses its rotation to either open or close the valve. The clutch and clutch
lever disconnects the electric motor from the gear assembly and allows the valve
to be operated manually with the handwheel.
Most electric motor actuators are equipped with limit switches,
torque limiters, or both. Limit switches de-energize the electric motor when the
valve has reached a specific position. Torque
limiters de-energize the electric motor when the amount of
turning force has reached a specified value. The turning force normally is
greatest when the valve reaches the fully open or fully closed position. This
feature can also prevent damage to the actuator or valve if the valve binds in
an intermediate position.
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