Question 151Steam Plants - 1st Asst/Chief

The correct answer is A) steam pressure acting on the enlarged area of projecting lip or ring. In a huddling chamber safety valve, once the initial lift of the valve disc occurs due to excessive static boiler pressure, the valve will continue to lift open further due to the steam pressure acting on the enlarged area of the projecting lip or ring. This increased area exposed to the steam pressure creates a reactive force that pushes the valve open further, allowing the excess pressure to be relieved. The other options are incorrect because: B) the reactive force is a result of the enlarged area, not the rapid expansion of escaping steam; C) there is no adjustable orifice ring in a huddling chamber safety valve; and D) the steam pressure is not transmitted through a pipe connected to the superheater outlet, but rather acts directly on the valve components.