Question 161Steam Plants - Assistant Engineer

The correct answer is C) To ensure that the valve will not be seized shut when hot. When an auxiliary boiler is lit off, the main steam stop valve is eased off its seat and then gently closed to ensure that the valve will not become seized shut when the boiler heats up. As the boiler warms up, the metal components will expand, and if the valve is left tightly closed, it may become stuck and unable to open when needed. Easing the valve off its seat and then closing it gently allows for this thermal expansion to occur without binding the valve. The other answer choices are incorrect because they do not address the primary reason for this procedure, which is to prevent the valve from seizing due to thermal expansion. Examining the valve stem, checking the bonnet seal, or inspecting the valve packing are not the main reasons for this practice.