You will understand after reading it!

A gate valve is a valve that can only be fully opened or fully closed. The opening and closing part of the gate valve is the valve disc. When the handwheel is turned, the valve disc will move up or down in a straight line to open or close, and to circulate or cut off the medium. It is generally composed of valve body, valve seat, valve stem, valve disc, valve bonnet, and sealing ring. The valves can be driven by handwheel or with actuators, like electrical actuator, pneumatic actuator.

The gate valve is not easy to block, so the gate valve is very suitable for the circulation of viscous materials such as mud, syrup, cement, garbage disposal, grease, etc.

Metal seated vs resilient seated gate valves

Before the resilient seated gate valve was introduced to the market, gate valves with a metal seated wedge were widely used. The conical wedge design and angular sealing devices of a metal seated wedge require a depression in the valve bottom to ensure a tight closure. Herewith, sand and pebbles are embedded in the bore. The pipe system will never be completely free from impurities regardless of how thoroughly the pipe is flushed upon installation or repair. Thus, any metal wedge will eventually lose its ability to be drop-tight. 

A resilient seated gate valve has a plain valve bottom allowing free passage for sand and pebbles in the valve. If impurities pass as the valve closes, the rubber surface will close around the impurities while the valve is closed. A high-quality rubber compound absorbs the impurities as the valve closes, and the impurities will be flushed away when the valve is opened again. The rubber surface will regain its original shape securing a drop-tight sealing.