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Hydraulic and Pneumatic Knowledge
Fluid Power Equipment
A typical electric solenoid actuator is shown below. It consists
of a coil, armature, spring, and stem.
The coil is connected to an external current supply. The spring
rests on the armature to force it downward. The armature moves vertically inside
the coil and transmits its motion through the stem to the valve.
When current flows through the coil, a magnetic field forms
around the coil. The magnetic field attracts the armature toward the center of
the coil. As the armature moves upward, the spring collapses and the valve
opens. When the circuit is opened and current stops flowing to the coil, the
magnetic field collapses. This allows the spring to expand and shut the valve.
A major advantage of solenoid actuators is their quick
operation. Also, they are much easier to install than pneumatic or hydraulic
actuators. However, solenoid actuators have two disadvantages. First, they have
only two positions: fully open and fully closed. Second, they don’t produce
much force, so they usually only operate relatively small valves.
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