How would the illustrated valve respond to a complete loss of charge from the remote bulb-to-control diaphragm power element if the valve is used as a temperature control valve for a steam-heated heavy fuel oil service heater? Refer to Illustration GS-0045

Correct Answer: Option B — The valve would fail in the fully-open position, resulting in a high fuel oil temperature alarm.

Loss of thermal charge in the remote bulb causes the bellows to collapse, removing the downward force on the diaphragm. Without this force, the internal spring mechanism drives the valve to the fully-open position, resulting in maximum steam flow and a high fuel oil temperature alarm condition.