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What factors need to be considered when purchasing valves? When purchasing valves, the practice of only specifying specifications, categories, and working pressures to meet the procurement requirements is imperfect in the current market economic environment. In order to compete for products, valve manufacturers have each carried out different innovations under the concept of unified valve design, forming their own corporate standards and product personalities. Therefore, when purchasing valves, it is necessary to put forward technical requirements in more detail and coordinate with manufacturers to achieve consensus as an attachment to the valve purchasing contract. 1. General requirements 1.1 Valve specifications and categories should comply with the requirements of pipeline design documents. 1.2 The model of the valve should indicate the national standard numbering requirements it is based on. If it is an enterprise standard, the relevant description of the model should be indicated. 1.3 The working pressure of the valve must be ≥ the working pressure of the pipeline. Without affecting the price, the working pressure that the valve can withstand should be greater than the actual working pressure of the pipeline. ； When the valve is closed, either side should be able to withstand 1.1 times the valve working pressure without leakage. ； When the valve is open, the valve body should be able to withstand twice the valve working pressure. 1.4 The valve manufacturing standard should indicate the national standard number it is based on. If it is an enterprise standard, the enterprise document should be attached to the procurement contract. 2. Valve quality standard 2.1 The valve body material should be mainly ductile iron, and the grade and actual physical and chemical testing data of the cast iron should be indicated. 2.2 Valve stem material, strive to be stainless steel stem (2CR13), large diameter valves should also be stainless steel embedded stems. 2.3 The nut material is made of cast aluminum brass or cast aluminum bronze, and its hardness and strength are greater than the valve stem. 2.4 The hardness and strength of the valve stem bushing material should be no greater than that of the valve stem, and it should not cause electrochemical corrosion with the valve stem and valve body when immersed in water. 2.5 Material of sealing surface ① Valve types are different, sealing methods and material requirements are different ； ②For ordinary wedge gate valves, the material, fixing method and grinding method of the copper ring should be explained. ； ③Soft seal gate valve, physical, chemical and hygienic testing data of valve plate rubber lining material ； ④The butterfly valve should indicate the material of the sealing surface of the valve body and the material of the sealing surface of the butterfly plate. ； Their physical and chemical testing data, especially the hygienic requirements, anti-aging properties, and wear resistance of rubber ； Usually, nitrile rubber and EPDM rubber are used, and it is strictly prohibited to mix recycled rubber. 2.6 Valve shaft packing ① Since the valves in the pipeline network usually open and close infrequently, the packing is required to be inactive for several years, the packing does not age, and the sealing effect is maintained for a long time. ； ②The valve shaft packing should also ensure good sealing effect when it withstands frequent opening and closing. ； ③In view of the above requirements, the valve shaft packing should not be replaced for life or for more than ten years. ； ④If the packing needs to be replaced, the valve design should consider measures to enable replacement under water pressure. 3. Variable speed transmission box 3.1 The box material and internal and external anti-corrosion requirements are consistent with the valve body principles. 3.2 The box should be sealed and can withstand immersion in a water column of 3 meters after assembly. 3.3 For the opening and closing limit device on the box, the adjusting nut should be inside the box or outside the box, but special tools are required to operate it. 3.4 The transmission structure is reasonably designed. It can only drive the valve shaft to rotate when opening and closing, and does not allow it to move up and down. The transmission components are properly engaged and do not cause separation and slippage when opening and closing under load. 3.5 The transmission box body and the valve shaft seal cannot be connected to form a leak-free whole, otherwise reliable measures to prevent cross-leakage should be taken. 3.6 There should be no debris in the box, and the gear engagement parts should be protected by grease. 4. Valve operating mechanism 4.1 The opening and closing direction of the valve operation should always be clockwise. 4.2 Since the valves in the pipeline network are often opened and closed manually, the number of opening and closing revolutions should not be too many. Even large-diameter valves should be within 200-600 revolutions. 4.3 In order to facilitate one person's opening and closing operation, the maximum opening and closing torque should be 240N-m under plumber's pressure. 4.4 The opening and closing operating end of the valve should be a square tenon with standardized dimensions and face the ground so that people can operate it directly from the ground. Valves with discs are not suitable for underground pipe networks. 4.5 Display panel of valve opening and closing degree ① The scale line of valve opening and closing degree should be cast on the gearbox cover or on the shell of the display panel after the direction is changed. They should all face the ground. The scale lines should be painted with fluorescent powder to make them eye-catching. ； ②The material of the indicator dial needle can be stainless steel plate if the management is good, otherwise it will be painted steel plate. Do not use aluminum skin. ； ③The indicator needle is eye-catching and firmly fixed. Once the opening and closing adjustment is accurate, it should be locked with rivets. 4.6 If the valve is buried deep and the operating mechanism and display panel are ≥1.5m away from the ground, extension rod facilities should be provided and firmly fixed to facilitate observation and operation from the ground. In other words, the opening and closing operations of valves in the pipeline network are not suitable for downhole operations. 5. Performance testing of valves 5.1 When valves of a certain specification are manufactured in batches, an authoritative organization should be entrusted to conduct the following performance testing: ①The opening and closing torque of the valve under working pressure ； ②Under working pressure conditions, the number of continuous opening and closing times that can ensure the valve is tightly closed ； ③Detection of the flow resistance coefficient of the valve under pipeline water transmission conditions. 5.2 The valve should undergo the following tests before leaving the factory: ①When the valve is open, the valve body should withstand an internal pressure test twice the working pressure of the valve. ； ②When the valve is closed, both sides bear 1.1 times the working pressure of the valve without leakage. ； However, the leakage value of metal-sealed butterfly valves is not greater than the relevant requirements. 6. Internal and external anti-corrosion of the valve 6.1 The inside and outside of the valve body (including the transmission box) should first be shot blasted, sanded and rust removed, and strive to electrostatically spray powdery non-toxic epoxy resin with a thickness of more than 0.3mm. When it is difficult to electrostatically spray non-toxic epoxy resin on extra large valves, similar non-toxic epoxy paint should also be applied by brushing or spraying. 6.2 The interior of the valve body and all parts of the valve plate require comprehensive anti-corrosion. On the one hand, it will not rust when immersed in water, and there will be no electrochemical corrosion between the two metals. ； On the other hand, the smooth surface reduces the water resistance. 6.3 The hygienic requirements for anti-corrosion epoxy resin or paint in the valve body should be tested by the corresponding authoritative agency. Chemical and physical properties should also meet relevant requirements. 7. Valve packaging and transportation 7.1 Light blocking plates should be installed on both sides of the valve to seal it. 7.2 Medium and small diameter valves should be tied with straw ropes and transported in containers. 7.3 Large-diameter valves are also solidly packaged in simple wooden frames to avoid damage during transportation. 8. Factory instructions for valves. Valves are equipment, and the following relevant data should be marked in the factory instructions.: Valve specifications ； model ； work pressure ； manufacturing standards ； Valve body material ； Stem material ； Sealing material ； Valve shaft packing material ； Valve stem bushing material ； Internal and external anti-corrosion materials ； Operation start direction ； Number of revolutions ； Opening and closing torque under working pressure ； Manufacturer's name ； Factory date ； Factory number ； weight ； The hole diameter, number of holes, and center hole distance of the connecting flange ； Graphically indicate the overall length, width, and height control dimensions ； Valve flow resistance coefficient ； Effective opening and closing times ； Relevant data of valve factory inspection and installation and maintenance precautions, etc.