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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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