A coil spring (52) is located within the through bore (36) of the valve seat (14, 26) and biases the valve closed.

Pressurized gas stored in the reservoirs (37, 39) is utilized to shift a gate member (20) from a valve open position to a valve closed position upon actuation of the valve.

The valve utilizes a negative pressure at the outlet chamber (108) that biases the valve closed until a sufficient column of water overcomes the bias.

Operators, looking at the indicator position of the relief valve, have seen “valve closed”: this information was false.

A closed valve can also prevent water from flowing properly within the boiler.

The force released by having the spring pass its transition temperature holds the valve closed against hydrostatic pressure.

The pressure force over the pressure compensated part keeps the valve closed.