Gate Valve And Stop Valve Maintenance Regulations
1. Introduction to Gate Valve
1.1. Working principle and function of gate valve:
Gate valve belongs to the category of cut-off valves, usually installed on pipes with a diameter greater than 100mm, to cut off or connect the flow of media in the pipe. Because the valve disc is in the gate type, it is generally called a gate valve. Gate valves have the advantages of labor-saving switching and low flow resistance. However, the sealing surface is easy to wear and leak, the opening stroke is large, and maintenance is difficult. Gate valves cannot be used as regulating valves 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 downward and relies on the gate valve sealing surface and the valve seat sealing surface to be highly smooth, flat and consistent, fit each other to prevent the flow of media, and rely on the top wedge to increase the sealing effect. Its closing piece moves vertically along the center line. There are many types of gate valves, which can be divided into wedge type and parallel type according to the type. Each type is divided into single gate and double gate.
1.2 Structure:
The gate valve body adopts a self-sealing form. The connection method between the valve cover and the valve body is to use the upward pressure of the medium in the valve to compress the sealing packing to achieve the purpose of sealing. The gate valve sealing packing is sealed with high-pressure asbestos packing with copper wire.
The gate valve structure is mainly composed of valve body, valve cover, frame, valve stem, left and right valve discs, packing sealing device, etc.
The valve body material is divided into carbon steel and alloy steel according to the pressure and temperature of the pipeline medium. Generally, the valve body is made of alloy material for valves installed in superheated steam systems, t＞450℃ or above, such as boiler exhaust valves. For valves installed in water supply systems or pipelines with medium temperature t≤450℃, the valve body material can be carbon steel.
Gate valves are generally installed in steam-water pipelines with DN≥100 mm. The nominal diameters of the gate valves in the WGZ1045/17.5-1 boiler in Zhangshan Phase I are DN300, DNl25 and DNl00.
