Valve is a fluid conveying system control components, with cut-off, regulation, diversion, to prevent countercurrent, voltage, shunt or overflow pressure relief functions. Valves for fluid control systems, ranging from the simplest cut-off valves to the most 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 mediums, mud, oil, liquid metals and radioactive media.

Valve According to the material is also divided into cast iron valves, cast steel valves, stainless steel valves, chromium-molybdenum steel valves, chromium-molybdenum vanadium steel valves, duplex steel valves, plastic valves, non-standard custom-made valve materials.

Valve purchase should pay attention to what technical requirements

1 Valve specifications and categories, should conform to the requirements of piping design documents 1.1 The type of valve should be indicated according to the national standard number requirements.

If the enterprise standard, should indicate the model of the relevant instructions.

1.2 Valve work pressure, requirements ≥ pipe work pressure, without affecting the price of the premise, the valve can withstand the pressure should be greater than the actual pipe pressure, the valve closed on either side should be able to withstand 1.1 times times the valve pressure value, but not leakage; valve opening condition, the valve body should be able to withstand twice times the requirements of valve pressure.

1.3 Valve manufacturing standards, should indicate the basis of the national standard number, if the enterprise standards, procurement contracts should be accompanied by enterprise documents

2 Choice valve Material 2.1 valve material, because the gray iron pipe is not recommended gradually, the valve body material should take the ductile iron as the main, and indicate the grade and the actual physical and chemical examination data of the casting.

2.2 Stem material, to stainless steel stem (2CR13), large diameter valves should also be stainless steel inlay the stem.

2.3 Nut material, using cast aluminum brass or cast aluminum bronze, and hardness and strength are greater than the stem

2.4 Stem bushing material, its hardness and strength should not be greater than the stem, and in the water immersion condition and valve stem, valve body does not form electrochemical corrosion. 2.5 Sealing surface Material ① valve category, sealing method and material requirements are different; ② ordinary wedge gate valve, copper ring material, fixed mode, grinding mode should be explained; ③ Soft sealed gate valve, valve plate lining material physical and chemical and sanitary testing data; ④ butterfly valve should be marked with the sealing surface material on the valve body and the sealing surface material on the butterfly board.

, their physical and chemical testing data, especially the hygienic requirements of rubber, anti-aging properties, wear-resistant properties, usually use of ding-eye rubber and EPDM rubber, etc., is strictly prohibited with recycled plastic. 2.6 Valve SHAFT FILLER ① because of the valve in the pipe net, it is usually not open and close frequently, requirements of fillers in a few years inactive, fillers are not aging, long-term to maintain the sealing effect; ② valve shaft fillers should also withstand frequent opening and closing, the sealing effect of good; ③ in view of the above requirements, valve shaft filler strive for a lifetime not to change or more than 10 years not to replace

 If the ④ filler needs to be replaced, the valve design should consider the measures of replacing under the condition of hydraulic pressure.