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A flow control valve regulates the flow or pressure
of a fluid. Control valves normally respond to
signals generated by independent devices such as
flow meters or temperature gauges.
Globe control valve with the pneumatic actuator and
smart positioner
Control valves are normally fitted with actuators
and positioners. Pneumatically-actuated globe valves
are widely used for control purposes in many
industries, although quarter-turn types such as
(modified) ball and butterfly valves are also used.
Control valves can also work with hydraulic
actuators (also known as hydraulic pilots). These
types of valves are also known as Automatic Control
Valves. The hydraulic actuators will respond to
changes of pressure or flow and will open/close the
valve. Automatic Control Valves do not require an
external power source, meaning that the fluid
pressure is enough to open and close the valve.
Automatic control valves include: pressure reducing
valves, flow control valves, back-pressure
sustaining valves, altitude valves, and relief
valves. An altitude valve controls the level of a
tank. The altitude valve will remain open while the
tank is not full and it will close when the tanks
reaches its maximum level. The opening and closing
of the valve requires no external power source
(electric, pneumatic, or man power), it is done
automatically, hence its name.
Control valve cavitation
Cavitation damage is characterised by a rough cinder
like appearance of the eroded surface.[1] Cavitation
can be treated by several means. The first is to
eliminate the cavitation by managing the pressure
drop. Specialist control valve trims can be used for
this purpose. A second method is to minimse the
damage by isolating the cavitation away from valve
surfaces and by hardening the surfaces it does
impact, the third way is to modify the process. |
