When the gate valve is closed, the sealing surface can be sealed solely by the medium pressure, meaning it relies on the medium pressure to push the sealing surface of the gate plate against the valve seat on the other side to ensure the sealing. This is known as self-sealing. Most gate valves use forced sealing, which means when the valve is closed, external force is needed to forcibly push the gate plate against the valve seat to ensure the sealing integrity of the sealing surface.

Operation Method: The gate plate of the gate valve moves linearly along with the valve stem, also known as a through-bolt gate valve. Typically, there is a trapezoidal thread on the lifting rod, which converts the rotational motion into linear motion through the nut at the top of the valve and the guide slots on the valve body, thus changing the operating torque into thrust. When opening the valve, when the lifting height of the gate plate equals 1:1 of the valve passage diameter, the fluid passage is completely open. However, this position is not observable during operation. In actual use, the top point of the valve stem is used as a reference, i.e., the position where it cannot be opened further, as its fully open position. To prevent locking due to temperature changes, it is usually turned back 1/2 to 1 turn after reaching the top point, which serves as the fully open position of the valve. Therefore, the fully open position of the valve is determined by the position of the gate plate (i.e., stroke). Some gate valves have the nut on the gate plate, where the handwheel rotation drives the valve stem to lift the gate plate, known as a rotating stem gate valve or a blind stem gate valve.