Gate valve opening and closing parts is the gate, the direction of movement of the gate and the fluid direction perpendicular to the gate valve can only be fully open and fully closed, can not be adjusted and throttling. The gate has two sealing surfaces, the two most commonly used mode gate valve sealing surface of the wedge, wedge angle with the valve parameters vary, usually 5 °, the medium temperature is not high when the 2 ° 52 '. Wedge gate valve can be made into a whole, called the rigid gate; can also be made to produce trace deformation of the gate to improve its craft, to make up the sealing surface angle in the processing of the deviation, The plate is called a flexible gate. When the valve is closed, the sealing surface can only rely on the media pressure to seal, that is, rely on the media pressure to the gate of the sealing surface to the other side of the valve seat to ensure that the sealing surface seal, which is self-sealing. Most of the gate valve is forced to seal, that is, when the valve is closed, to rely on external force forced to the gate pressure to the valve seat to ensure that the sealing surface of the seal. Gate valve with the stem with a straight line for movement, called the lift bar gate valve, also called the gate valve. Usually in the lift bar with trapezoidal thread, through the top of the valve nut and the valve body on the guide groove, the rotary motion into a linear motion, that is, the operating torque into the operating thrust. When the valve is opened, when the lift height is equal to 1: 1 times the diameter of the valve, the fluid channel is completely open, but this position can not be monitored during operation. The actual use of the stem is the vertex as a sign, that is, the location of the open, as its full open position. In order to consider the temperature changes appear locking phenomenon, usually in the open to the vertex position, and then back 1 / 2-1 circle, as the full valve position. Therefore, the valve fully open position, according to the location of the gate that is to determine the trip. Some gate valve, stem nut set on the gate, hand wheel rotation to drive the stem rotation, leaving the gate to lift, this valve is called the rotary bar gate valve, or called the dark bar gate valve.