A gate valve is a valve that opens by lifting a round or rectangular gate out of the path of the fluid. The gate valve has sealing surfaces between the gate and seats that are planar, leading to gate valves being used when a straight-line flow of fluid and minimum restriction is desired. Generally, gate valves are used to permit or prevent the flow of liquids, for example in a pipe line system.
Liquid is able to flow when the gate of the gate valve is linearly retracted to open the flow path, whereas the liquid is prevented from flowing when the gate is linearly extended to a closed position. In the closed position liquid impinges a front side face of the gate and is prevented from passing between the gate and a body of the gate valve by rubber valve liners that surround the gate. Typically, the rubber valve liners are fixed in the body of the gate valve and rub against the gate as the gate opens and closes causing the rubber valve liners to wear away and lose their sealing ability. Furthermore, increasing compression of the rubber valve liners against the gate increases the wear rate of the rubber valve liners. Some gate valves employ spring components to maintain compression of the rubber valve liners, but compression force decreases as the rubber valve liners wear.