This invention relates generally to a fluid valve and more particularly to a switching logic element having a normally closed characteristic.
Switching logic elements utilize an unbalanced poppet which is spring loaded on a seat; however, without additional fluid pressure to bias the poppet against the seat, flow can occur between the input and output ports. These valves are called "normally open" because of the need for fluid pressure to close them. The complementary logic element--normally closed--has not previously been available. Such a normally closed logic element would require a positive or pilot pressure input to be opened and to remain open.
The need for a pilot pressure is an operating requirement for fail safe applications, i.e. if the source of fluid pressure is cut off either inadvertently or because of system shut down, the valve should close to prevent loss of load supporting pressure by flow through the logic element.