Gate valves are cut-off valves and are usually installed on pipes with a diameter greater than 100mm to cut off or connect the flow of medium in the pipe. Because the disc is a gate type, it is commonly called a gate valve. The gate valve has the advantages of low switching effort and low flow resistance. But the sealing surface is easy to wear and leak, the opening stroke is large, and the maintenance is difficult. The gate valve cannot be used as a regulating valve and must be in the fully open or fully closed position. The working principle is: when the gate valve is closed, the valve stem moves downwards, relying on the sealing surface of the gate valve and the seat of the valve to be highly smooth, flat and consistent. They can prevent the medium from flowing through, and rely on the top wedge to increase the sealing effect. The closing part moves along the vertical direction of the center line. There are many types of gate valves, which can be divided into wedge type and parallel type according to their types. Each type is divided into single gate and double gate.
The valve body of the gate valve adopts a self-sealing form. The connection between the bonnet and the valve body is to use the upward pressure of the medium in the valve to force the sealing packing to be compressed to achieve the purpose of sealing. The gate valve packing is sealed with high-pressure asbestos packing with copper wire.
The gate valve structure is mainly composed of the valve body, the valve cover, the frame, the valve stem, the left and right discs, and the packing seal device.
The valve body material is divided into two types: carbon steel and alloy steel according to the pressure and temperature of the pipeline medium. Generally installed in the valve of superheated steam system, t>450鈩, the valve body is made of alloy material, such as boiler exhaust valve. For valves installed in water supply systems or pipelines with medium temperature t鈮450鈩, the valve body material can be carbon steel.
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