🔍 Key Concepts

• Pressure reducing valve operation – how spring force and downstream pressure balance on the diaphragm. • Direction of movement when downstream pressure is TOO LOW versus TOO HIGH. • Interaction between diaphragm E, pilot valve D, and main valve / spring A in this style of valve.

💭 Think About

• Picture what forces are acting on diaphragm E when the downstream pressure drops below the setpoint: does the spring above it push it up or down? • If diaphragm E moves that way, what must happen to pilot valve D and to the main valve and its spring A in order to increase downstream pressure back to the preset value? • Ask yourself: to raise low downstream pressure, should the valve open more or close more, and what does that do to the compression of spring A?

✅ Before You Answer

• Be clear on which side of diaphragm E the downstream pressure is acting in the illustration. • Trace the motion: adjusting screw and spring on top → diaphragm E → stem → valve D → main valve and spring A. • Confirm whether each statement (A, B, C) matches the motion needed to OPEN the valve further to restore downstream pressure; only select “all of the above” if each one is consistent with that motion.