The working principle of a gate valve

The gate valve's closing member is a gate, and the gate's movement direction is perpendicular to the fluid direction. Gate valves can only be fully opened or fully closed; they cannot be used for regulation or throttling. The gate has two sealing surfaces. In the most common design, the two sealing surfaces of the gate valve form a wedge; the wedge angle varies with the valve parameters, usually 5°, or 2°52' when the medium temperature is not high. The wedge gate's gate can be made as a whole, called a rigid gate; it can also be made into a gate that can produce a small amount of deformation to improve its processability and compensate for deviations in the sealing surface angle during processing. This type of gate is called an elastic gate. When the gate valve is closed, the sealing surface can rely solely on the medium pressure for sealing; that is, the medium pressure presses the sealing surface of the gate against the valve seat on the other side to ensure the sealing of the sealing surface. This is self-sealing. Most gate valves use forced sealing; that is, when the valve is closed, external force is required to forcibly press the gate against the valve seat to ensure the sealing of the sealing surface. The gate of a gate valve moves linearly with the stem; this is called a rising stem gate valve, or an outside screw gate valve. There is usually a trapezoidal thread on the rising stem. Through the nut at the top of the valve and the guide groove on the valve body, the rotary motion is converted into linear motion, that is, the operating torque is converted into operating thrust. When opening the valve, when the gate lift height is equal to 1:1 times the valve diameter, the fluid passage is completely unobstructed; however, this position cannot be monitored during operation. In actual use, the apex of the stem is used as a mark, and the position where it cannot be opened further is used as its fully open position. To consider the phenomenon of locking due to temperature changes, it is usually necessary to turn back 1/2-1 turn at the top position to set the fully open valve position. Therefore, the fully open position of the valve is determined according to the position or stroke of the gate. In some gate valves, the valve stem nut is located on the gate. The handwheel rotates to drive the valve stem to rotate, thus lifting the gate. This type of valve is called a non-rising stem gate valve, or an inside screw gate valve.