In a pressure reducing valve, the two upper operating chambers are sealed from each other by a

• A. Rigid metal plate
• B. Elastomeric gasket
• C. Flexible, reinforced diaphragm
• D. Piston and cylinder

Answer: (C)

The two upper operating chambers are separated by a flexible, reinforced diaphragm. This diaphragm acts as a compliant barrier that keeps the high-pressure side and the regulated side from mixing while still allowing pressure changes to be transmitted to the valve mechanism. Its flexibility lets the diaphragm bend and move as the upstream pressure tries to push it against the downstream side, which in turn modulates the valve opening to maintain the desired downstream pressure. The reinforcement helps it withstand repeated pressure cycling and tearing, improving durability. A rigid metal plate wouldn’t allow the necessary movement, an elastomeric gasket is typically a static seal, and a piston and cylinder represents a different valve design.