What technical standards need to be considered when buying a valve

For this reason, this draft is drafted for discussion and whether it can be communicated within the industry after the revision, which arouses the attention of various companies in this regard and improves their work in this area.
1. The valve specifications and categories should meet the requirements of the pipeline design documents.
1.2; The valve model should be marked with the national standard number requirements. If it is a corporate standard, the relevant description of the model should be indicated. 
1.3; The working pressure of the valve is required to be ≥ the working pressure of the pipeline. Under 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 valve working pressure.
1.4; The valve manufacturing standard should state the number of the national standard on which it is based. If it is a corporate standard, the purchase contract should be accompanied by corporate documents
2. Material of valve
2.1; Valve material, as gray cast iron pipes are gradually not recommended, the valve body material should be mainly ductile iron, and the grade and actual physical and chemical testing data of the casting should be indicated. 
2.2; The material of the valve stem is to strive for a stainless steel stem (2C). 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 the hardness and strength are greater than the valve stem
2.4; The material of the valve stem bushing shall have a hardness and strength not greater than that of the valve stem, and it shall not form electrochemical corrosion with the valve stem and valve body under water immersion.
2.5; Material of sealing surface ①Valve types are different, sealing method and material requirements are different; ②Common wedge gate valve, copper ring material, fixing method, and grinding method should be explained; ③Soft sealing gate valve, valve plate lining material The physical, chemical and hygienic testing data of the butterfly valve; ④The butterfly valve should indicate the sealing surface material on the valve body and the sealing surface material of the butterfly plate; their physical and chemical testing data, especially the hygienic requirements, anti-aging performance, and wear resistance of rubber; usually used It is strictly forbidden to mix reclaimed rubber with nitrile butadiene rubber and EPDM rubber. 
2.6; Valve shaft packing ① Since the valves in the pipe network are usually opened and closed infrequently, the packing is required to be inactive for several years and the packing shall not be aged, so as to maintain the sealing effect for a long time; ② The valve shaft packing should also be subjected to frequent opening and closing. When closed, the sealing effect is good; ③In view of the above requirements, the valve shaft packing should not be replaced for life or more than ten years; ④If the packing needs to be replaced, the valve design should consider measures that can be replaced under water pressure.
3. Variable speed transmission box
3.1; The material of the box body and the internal and external anti-corrosion requirements are consistent with the valve body principles. 
3.2; The box body should have sealing measures, and the box body can withstand 3 meters of water column immersion after assembly.
3.3 The adjustment nut of the opening and closing limit device on the box body should be inside the box body. 
3.4; The design of the transmission structure is reasonable, and the valve shaft can only be driven to rotate when opening and closing, without making it move up and down, and the transmission parts will bite properly, and no separation and slippage will occur when opening and closing under load.   3.5; The variable speed transmission box and the valve shaft seal cannot be connected as a leak-free whole. 
3.6; There is no debris in the box, and the gear bite part should be protected by grease. 
4. Valve operating mechanism
4. The opening and closing direction of the valve should always be closed clockwise.  4.2 Due to the valves in the pipe network,
It is often manual opening and closing, and the number of opening and closing revolutions should not be too much. Even large-diameter valves should also be within 200-600 revolutions. 4.3; In order to facilitate one person’s opening and closing operations, the maximum opening and closing torque should be 240m-m under the pressure of the pipeline.
4.4; The opening and closing end of the valve should be a square tenon, with a standardized size, and face the ground so that people can directly operate it from the ground. The attached valve is not suitable for underground pipe network. 
4.5; Display panel of valve opening and closing degree
①The scale line of the valve opening and closing degree should be cast on the cover of the gearbox or on the shell of the display panel after changing the direction, all facing the ground, and the scale line should be painted with phosphor to show it eye-catching; ②The material of the indicator disc needle is Stainless steel plate can be used under good management, otherwise it is painted steel plate, do not use aluminum skin; ③The indicator needle is eye-catching and fixed firmly. Once the opening and closing adjustment is accurate, it should be locked with rivets.
4.6; If the valve is buried deeply, and the distance between the operating mechanism and the display panel is ≥15m from the ground, an extension rod facility shall be provided and it shall be firmly fixed so that people can observe and operate it from the ground. In other words, the opening and closing operations of valves in the pipe network are not suitable for downhole operations. 
5Performance testing of valves
5.1; When a valve is manufactured in batches of a certain specification, an authoritative organization should be entrusted to carry out the following performance testing: ①The opening and closing torque of the valve under working pressure; ②Under working pressure, the valve can be closed tightly and continuously. The number of closures; ③The detection of the flow resistance coefficient of the valve under the condition of water delivery in the pipeline.
5.2; The valve should be tested as follows before leaving the factory: ①When the valve is open, the valve body should withstand the internal pressure test that is twice the valve working pressure; ②When the valve is closed, the two sides should withstand 11 times respectively. Valve working pressure value, no leakage; but metal-sealed butterfly valve, the leakage value is not greater than the relevant requirements
6The internal and external anticorrosion of the valve
6.1; The inside and outside of the valve body (including the variable speed transmission box) should be shot blasted to clean the sand and rust, and strive to electrostatically spray the powdery non-toxic epoxy resin with a thickness of more than 03mm. When it is difficult to electrostatically spray non-toxic epoxy resin for extra-large valves, similar non-toxic epoxy paint should be brushed or sprayed.
6.2; The inside of the valve body and all parts of the valve plate require comprehensive anti-corrosion. On the one hand, it will not corrode when immersed in water, and no electrochemical corrosion will occur between the two metals; on the other hand, the smooth surface will reduce the water resistance.
6.3; The sanitary requirements for the anticorrosive epoxy resin or paint in the valve body shall have a test report from the corresponding authority. The chemical and physical properties should also meet the relevant requirements. 
7. Valve packaging and transportation
7.1; Lightweight blocking plates should be installed on both sides of the valve for solid sealing. Medium and small diameter valves should be bundled with straw ropes and transported in containers.
7.3; Large-caliber valves are also packaged with simple wooden strips and frame-retained to avoid damage during transportation
8The factory manual of the valve
Valves are equipment. The following relevant data should be indicated in the factory instructions: Valve specifications; model; working pressure; manufacturing standards; valve body material;; valve stem material; sealing material; valve shaft packing material; valve stem sleeve material; Anti-corrosion material; operating starting direction; number of revolutions; opening and closing torque under working pressure;
The name of the manufacturer; the date of manufacture; the number of the manufacture: weight; the diameter, number of holes, and center hole distance of the connecting flange
Indicates the overall length, width, and height control dimensions in the form of icons; the number of effective openings and closings
Valve flow resistance coefficient; relevant data of valve factory inspection and precautions for installation and maintenance, etc.

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