Question 283Steam Plants - 1st Asst/Chief

The correct answer is C) high steam pressure. In an automatically fired auxiliary boiler, the solenoid valves in the fuel oil supply line are automatically closed in response to high steam pressure to prevent overpressurization of the boiler system. This is a safety feature to shut off the fuel supply when the boiler reaches its maximum designed steam pressure, preventing a potentially dangerous situation. The other answer choices are incorrect because they do not directly relate to the automatic closure of the fuel oil solenoid valves. A decrease in feed temperature, high furnace air pressure, or low steam pressure would not directly trigger the closure of the fuel oil supply valves in the same way that high steam pressure would.