how do gate valves work
Gate valve refers to the valve whose closure (gate) moves vertically along the central line of the passage. Gate valves in the pipeline can only be used for full opening and closing, not for regulation and throttling. Gate valve is a kind of valve with a wide range of applications. It is usually used for blocking devices with diameters of DN (> 50mm), and sometimes for blocking devices with very small diameters. Gate valve is used as a cut-off medium. When it is fully open, the whole is smooth and longitudinal, and the pressure loss of medium operation is the smallest. Gate valves are usually used in situations where they do not need to be opened or closed frequently and keep the gate fully open or closed. It is not used for regulating or throttling. For high-speed moving medium, the vibration of the gate can be caused by the partial opening of the gate, and the vibration may damage the sealing surface of the gate and the seat, and the throttling will cause the gate to be eroded by the medium. From the structural form, the main difference is the form of sealing elements used. According to the form of sealing elements, gate valves are often divided into several different types, such as wedge gate valves, parallel gate valves, parallel double gate valves, wedge double gate valves and so on.
The most commonly used forms are wedge gate valves and parallel gate valves.
1. The gate has two sealing surfaces. The two sealing surfaces of the most commonly used mode gate valves form wedges. The wedge angle varies with the valve parameters, usually 50, when the medium temperature is not high. Wedge gate valve can be made into a whole, called rigid gate; it can also be made into a gate that can produce slight deformation to improve its workability and make up for the deviation of sealing surface angle in the process of processing. This kind of gate is called elastic gate.
2. When the gate valve is closed, the sealing surface can be sealed only by medium pressure, that is to say, the sealing surface of the gate can be pressed to the seat on the other side to ensure the sealing surface, which is self-sealing. Most gate valves are forced to seal, that is, when the valve is closed, the gate must be forced to the seat by external force to ensure the sealing surface.
3. The gate of the gate valve moves in a straight line with the stem, which is called the lift bar gate valve (also known as the open bar gate valve). Usually there are trapezoidal threads on the lifting rod. Through the real nut on the top of the valve and the guide groove on the valve body, the rotary motion is changed into linear motion, that is to say, the control torque is changed into the control thrust.
4. When opening the valve, when the gate elevation is 1:1 times of the valve diameter, the fluid passage is completely open, but in operation, this position can not be supervised. In practical use, the vertex of the valve stem is used as the sign, that is, the position of the valve stem that is not moving is used as its full open position. In order to consider the lock phenomenon caused by temperature change, the valve is usually opened to the vertex position and reversed to 1/2-1 turn as the position of the fully open valve. Therefore, the full open position of the valve is determined by the position of the gate (i.e. stroke).