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INTERNAL
PILOT-ACTUATED PRESSURE-REDUCING VALVES.-The internal pilot-actuated
pressure-reducing valve, shown in figure 13-28, uses a pilot valve to control
the main valve. The pilot valve controls the flow of upstream fluid, which is
ported to the pilot valve, to the operating piston, which operates the main
valve. The main valve is opened by the operating piston and closed by the main
valve spring. The pilot valve opens when the adjusting spring pushes down-ward
on the pilot diaphragm. It closes when downstream pressure exerts a force that
ex-ceeds the force of the adjusting spring. When the pilot valve shuts off or
throttles the flow of upstream fluid to the operating piston, the main valve
then pushes the valve and stem up-ward to throttle or close the main valve.
When downstream pressure falls below the set point, the adjusting spring force
acts downward on the diaphragm. This action overcomes the force of the
downstream system pressure, which is acting upward on the diaphragm. This opens
the pilot valve, allowing upstream pressure to the top of the operating piston
to open the main valve.
Figure 13-28.-Internal pilot-actuated pressure-reducing valve. |
 
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