Suppose the illustrated self-contained, internal-pilot, piston-operated temperature control valve is part of the temperature control system for a steam-heated heavy fuel oil service heater for a steam boiler. If there was an increase in demand for fuel by the boiler, what statement correctly represents how the valve would initially respond? GS-0045

Correct Answer: Option B — The fuel oil heater fuel outlet temperature would decrease, causing the remote bulb pressure to decrease and the control diaphragm to flex upward and through lever action, further open the pilot valve.

Increased fuel demand cools the oil, reducing the remote bulb pressure. This causes the diaphragm to flex upward, which, through the mechanical lever linkage, further opens the pilot valve. Increased pilot flow then opens the main valve to supply more steam, thereby raising the fuel oil temperature.