The valve is a control part in the fluid conveying system, which has the functions of cut-off, regulation, diversion, prevention of backflow, voltage stabilization, diversion or overflow and pressure relief. Valves used in fluid control systems, from the simplest shut-off valve to various valves used in extremely complex automatic control systems, have a wide variety and specifications. Valves can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, mud, oil, liquid metal and radioactive media. Valves are also divided into cast iron valves, cast steel valves, stainless steel valves, chrome molybdenum steel valves, chrome molybdenum vanadium steel valves, duplex steel valves, plastic valves, and non-standard customized valve materials according to their materials.

 

1. Valve specifications and categories, in line with the requirements of pipeline design documents: 1.1 The model of the valve should be marked with the requirements of the national standard number. If it is an enterprise standard, the relevant description of the model should be indicated. 1.2 The working pressure of the valve is required to be greater than the working pressure of the pipeline. On the premise of not affecting the price, the working pressure that the valve can withstand should be greater than the actual working pressure of the pipeline; any side of the valve should be able to withstand 1.1 times the working pressure of the valve when the valve is closed. pressure value without leakage; when the valve is open, the valve body should be able to withstand twice the working pressure of the valve.

 

2. Select the material of the valve: 2.1 The material of the valve, since the gray cast iron pipe is gradually not recommended, the material of the valve body should be mainly ductile iron, and the grade and the actual physical and chemical test data of the casting should be indicated. 2.2 The material of the valve stem should be made of stainless steel (2CR13). Large-diameter valves should also be stainless steel embedded valve stems. 2.3 The material of the nut is cast aluminum brass or cast aluminum bronze, and its hardness and strength are greater than that of the valve stem. 2.4 The material of the valve stem bushing, its hardness and strength should not be greater than that of the valve stem, and it should be The valve body does not form galvanic corrosion. 2.5 The material of the sealing surface ① The valve types are different, and the sealing method and material requirements are different; ② For ordinary wedge gate valves, the material, fixing method and grinding method of the copper ring should be explained; Physical chemical and hygienic testing data; ④ Butterfly valves should be marked with the material of the sealing surface on the valve body and the material of the sealing surface on the butterfly plate; their physical and chemical testing data, especially the hygienic requirements, anti-aging performance, and wear resistance of rubber; Eye rubber and EPDM rubber, etc., it is strictly forbidden to mix with reclaimed rubber. 2.6 Valve shaft packing ①Because the valves in the pipe network are usually opened and closed infrequently, the packing is required to be inactive for several years, the packing will not age, and the sealing effect will be maintained for a long time; ②The valve shaft packing should also withstand frequent opening and closing. , the good sealing effect; ③ In view of the above requirements, the valve shaft packing should not be replaced for life or more than ten years; ④ If the packing needs to be replaced, the valve design should consider measures to replace it under the condition of water pressure.

 

3. Variable speed transmission box: 3.1 The material of the box body and the requirements for internal and external anticorrosion are consistent with the principle of the valve body. 3.2 The box body should have sealing measures, and the box body can withstand the immersion of 3 meters of water column after assembly. 3.3 For the opening and closing limit device on the box, its adjusting nut should be in the box. 3.4 The design of the transmission structure is reasonable. When opening and closing, it can only drive the valve shaft to rotate, not to make it move up and down.