In the illustrated huddling-chamber safety valve, what statement is true concerning the opening and closing forces acting upon the disc? Illustration SG-0018

Correct Answer: Option C — The spring force acting downward on the disc is a valve opening force, and the sensed pressure acting upward on the disc is a valve closing force.

Spring force acts downward on the disc to keep the valve closed against system pressure. Sensed pressure acts upward on the disc area. When upward force exceeds the downward spring force, the valve opens. This mechanical balance is fundamental to the operation of spring-loaded safety valves under 46 CFR requirements.