Question 112Motor Plants - QMED

The correct answer is B) steam pressure sensing device with linkage to the damper air vanes. In an automatically fired auxiliary boiler, the fuel oil metering valve is controlled by a steam pressure sensing device. This device monitors the steam pressure in the boiler and adjusts the damper air vanes accordingly to maintain the desired steam pressure. As the steam pressure rises, the sensing device signals the damper air vanes to restrict the air supply, which in turn reduces the fuel oil flow through the metering valve. This closed-loop control system helps maintain stable boiler operation. The other options are incorrect because they do not accurately describe the control mechanism for the fuel oil metering valve in an automatically fired auxiliary boiler. Option A refers to a pressure magnifying device in the steam coil outlet, which is not the primary control mechanism. Option C mentions a metering device in the air supply line, which is not the direct control for the fuel oil valve. Option D refers to a signal from the feedwater electrode, which is not related to the fuel oil metering valve control.