What is the probable cause of hydraulically operated check valve fails to open?

• A. Worn seat
• B. Damaged diaphragm
• C. Debris in valve
• D. Frozen fluid

Answer: (B)

In a hydraulically operated check valve, opening is driven by hydraulic pressure acting on a flexible diaphragm that shifts the valve element away from its seat. If the diaphragm is damaged, it can’t flex properly or may fail to transmit the hydraulic force effectively, so applying pressure won’t move the valve to the open position. That direct loss of actuation makes a damaged diaphragm the most likely cause of the valve failing to open.

Worn seats affect sealing and the ability to hold pressure, not the actuation itself; debris can jam movement but the primary failure mode for not opening is inadequate actuation from a compromised diaphragm. Frozen fluid could impede movement, but the root issue remains the damaged diaphragm preventing proper actuation.