Question 149Steam Plants - 1st Asst/Chief

The correct answer is A) The principle by which blow down is accomplished. The primary operational difference between a nozzle reaction safety valve and a huddling chamber safety valve is the principle by which the blow down (reduction in pressure after the valve has opened) is accomplished. In a nozzle reaction valve, the blow down is achieved through the nozzle reaction, while in a huddling chamber valve, the blow down is accomplished through the pressure differential created in the huddling chamber. This fundamental difference in the blow down mechanism is the key distinction between these two types of safety valves. The other answer choices, B, C, and D, are not the primary operational difference, as they focus on other valve characteristics rather than the mechanism of blow down.