🔍 Key Concepts

• Force = Pressure × Area (F = P × A) and how changing the area affects the force available to move the main valve disc • How a pressure‑reducing / regulating valve uses an operating piston or diaphragm to control a larger main valve • Which side’s pressure (upstream high pressure vs downstream reduced pressure) is acting on piston "H" in the illustration

💭 Think About

• Trace the small passageways in the drawing: does piston "H" appear to be sensing upstream (inlet) or downstream (outlet) pressure? How can you tell? • If the piston surface area is larger than the main valve disc, what does that do to the force produced by a lower pressure acting on it compared with a higher pressure acting on a smaller area? • In normal operation of a pressure‑reducing valve, is the main valve motion controlled by the high‑pressure inlet side or the reduced‑pressure outlet side?

✅ Before You Answer

• Identify which pressure (inlet or outlet) actually acts on piston "H" by following the porting marked near "J" and the outlet arrow. • Apply F = P × A: with a larger area piston and a smaller area valve disc, which pressure can still develop enough force to move the main valve? • Make sure the option you choose matches the idea that a relatively small pressure is able to control a larger flow/pressure through the main valve.