Automatic Valves
This type of valves operate in conjunction with an automatic controller or device to control
the fluid flow. These controllers are also called as actuators. There are several types of
actuators commonly used:
a. Solenoid
b. Electric motor
c. Pneumatic
Such actuators will have gears, rack-and-pinion, cams and linkages to convert movement
and allow opening and closing of the valve stem.
a. Solenoid Valve
This type of valve only allows either a totally open or close position. It has a
magnetic coil which will lifts or drops a plunger in the valve to open and close the
flow of water. This occurs when the coil is either energized or de-energized.
Such valves are generally used for pipe sizes up to 50mm only. They are suitable
for small fan coil units which require water shut-off when the fan coil is switched
off.
solenoid coil
b. Electric Motorised Valve
The actuator has a built-in motor to produce a rotary motion. By using gears,
cams or linkages, the valve stem will be opened or closed. Usually, the motor runs
on DC power supply (24V).
Generally, the actuator has positioning controls whereby the valve can stroke to
any position between fully close to fully open. This is accomplished with a control
signal from an external feedback controller.
With this feature, it is possible to vary the water flow rate to suit any demand load
of an application.
Nevertheless, the cost of such valves is high.
Section 3 Page 45
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