In order for the reducing valve, shown in the illustration, to properly function, a control port is utilized between __________. See illustration GS-0044.
• Pressure-reducing valve operation – the valve must sense the pressure it is trying to control • Function of diaphragm E and spring F in opening/closing the main valve • Role of the small control port/pilot passage shown at label C in the illustration
• Ask yourself: Does a reducing valve need to sense upstream (inlet) pressure or downstream (outlet) pressure in order to keep outlet pressure constant? • Look carefully at passage C in the drawing: which two spaces does this drilled passage actually connect? Follow it from one side to the other. • What is sitting directly under diaphragm E, and how does a change in that pressure move the stem connected to piston H?
• Verify which side of the valve (inlet or outlet) the pressure under diaphragm E comes from. • Confirm that the control passage shown at C is not just an external line, but a drilled port linking two internal cavities. • Make sure the space at the top of piston H is open to a spring chamber/atmosphere, not to the controlled-pressure sensing line.
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