The practice of merely specifying the specifications, categories and working pressure when purchasing valves to meet the procurement requirements is not sufficient in the current market economy environment. This is because valve manufacturers, in order to compete in the market, each conduct different innovations under the unified design concept of the valves, forming their own enterprise standards and product characteristics. Therefore, it is very necessary to propose more detailed technical requirements during the valve procurement process, coordinate with the manufacturers to reach a consensus, and include them as an attachment to the valve procurement contract.
1. General Requirements
1.1 The specifications and categories of the valves should comply with the requirements of the pipeline design documents.
1.2 The model of the valve should indicate the corresponding national standard number it follows. If it is an enterprise standard, the relevant description of the model should be provided.
1.3 The working pressure of the valve should 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; at any side when the valve is closed, it should be able to withstand 1.1 times the valve's working pressure without leakage; when the valve is open, the valve body should be able to withstand twice the valve's working pressure requirement.
1.4 The manufacturing standards for valves should specify the corresponding national standard number. If it is an enterprise standard, the enterprise document should be attached to the purchase contract.
2. Valve Quality Mark
2.1 The material of the valve body should mainly be ductile iron. The brand name and the actual physical and chemical test data of the cast iron should also be specified.
2.2 Valve stem material: We aim to use stainless steel valve stems (2CR13). For large-diameter valves, stainless steel embedded stems should also be used.
2.3 The material of the nuts is cast aluminum brass or cast aluminum bronze, and both the hardness and strength are greater than those of the valve stem.
2.4 The material of the valve stem bushing should have a hardness and strength no greater than that of the valve stem. Moreover, it should not cause electrochemical corrosion with the valve stem and valve body when exposed to water immersion.
2.5 Material of the sealing surface ① The valve types vary, and the sealing methods and material requirements also vary; ② For ordinary wedge gate valves, the material of the copper ring, the fixation method, and the grinding method should all be specified; ③ For soft-sealing gate valves, the physical and chemical as well as hygiene test data of the rubber material used for the valve plate lining; ④ For butterfly valves, the material of the sealing surface on the valve body and the sealing surface on the butterfly plate should be indicated; their physical and chemical test data, especially the hygiene requirements, anti-aging performance, and wear resistance of the rubber; generally, nitrile rubber and ethylene propylene diene monomer rubber are used, and recycled rubber is strictly prohibited.
2.6 Valve Shaft Packing ① Since the valves in the pipeline network are usually not operated frequently, the packing is required to remain inactive and not age over several years, maintaining the sealing effect for a long time; ② The valve shaft packing should also ensure good sealing performance when subjected to frequent opening and closing; ③ Given these requirements, the valve shaft packing is aimed to be replaced for life or not replaced for more than ten years; ④ If the packing needs to be replaced, the valve design should consider measures for replacement under water pressure conditions.
3. Variable-speed transmission box
3.1 The material of the box body and the requirements for internal and external anti-corrosion are consistent with those of the valve body.
3. The box body should have a sealing measure. After assembly, the box can withstand immersion under a water column of 3 meters.
3.3 The opening and closing limit device on the box body should have its adjusting nut either inside the box or outside the box. However, it can only be operated with special tools.
3.4 The transmission structure is well-designed. During opening and closing, it can only cause the valve shaft to rotate without causing it to move up and down. The transmission components fit perfectly, and there is no slippage or disengagement when the valve is opened or closed under load.
3.5 The sealing area between the variable-speed transmission housing and the valve shaft must not be connected as a leak-free unit; otherwise, reliable measures to prevent leakage from occurring should be in place.
3. There should be no debris inside the box. The meshing areas of the gears should be protected by lubricating grease.
4. Operating mechanism of the valve
4.1 When operating the valve, the opening and closing directions should all be clockwise.
4.2 Due to the fact that the valves in the pipeline are often operated manually, the number of times they are opened and closed should not be excessive. Even for large-diameter valves, the opening and closing speed should be within 200 to 600 revolutions.
4.3 To facilitate the manual opening and closing operation by one person, under the working pressure condition of the pipeline, the maximum opening and closing torque should be 240 N-m.
4.4 The opening and closing operation ends of the valves should be square tenons, with standardized dimensions, and should face the ground so that people can operate them directly from the ground level. Valves with a wheel disc are not suitable for underground pipelines.
4.5 Display panel for valve opening and closing degree ① The scale lines for valve opening and closing degree should be cast on the gearbox cover or the outer shell of the display panel after the direction change, all facing the ground. The scale lines should be painted with fluorescent powder to be eye-catching; ② The material of the indicator needle can be stainless steel plate under better management conditions, otherwise it should be painted steel plate. Do not use aluminum sheet for making; ③ The indicator needle should be 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 at a deep level and the distance from the operating mechanism and display panel to the ground is ≥ 1.5m, an extension rod facility should be provided and firmly fixed to enable people to observe and operate from the ground. That is to say, the opening and closing operation of valves in the pipeline network is not suitable for underground operations.
5. Performance testing of valves
5.1 When manufacturing a certain specification of valves in batches, an authoritative institution should be entrusted to conduct the following performance tests: ① The opening and closing torque of the valve under working pressure; ② The number of consecutive opening and closing operations that can ensure the valve is tightly closed under working pressure; ③ The detection of the flow resistance coefficient of the valve under water transmission conditions in the pipeline.
5.2 Before leaving the factory, the valves should undergo the following tests: ① When the valve is in the open position, the valve body should be subjected to an internal pressure test at twice the working pressure of the valve; ② When the valve is in the closed position, each side should be subjected to 1.1 times the working pressure of the valve without any leakage; however, for metal-sealed butterfly valves, the leakage value should not exceed the relevant requirements.
6. Anti-corrosion treatment of the valve's interior and exterior
6.1 For the valve body (including the transmission box), both the inside and outside should be subjected to shot blasting to remove sand and rust. Then, apply electrostatic spraying of fine powder-free toxic epoxy resin with a thickness of more than 0.3mm. If it is difficult to conduct electrostatic spraying on extremely large valves, similar non-toxic epoxy paint should be brushed or sprayed instead.
6.2 The interior of the valve body and all parts of the valve plate must be fully protected against corrosion. Firstly, they will not rust even when immersed in water, and there will be no electrochemical corrosion between the two metals. Secondly, the smooth surface reduces the resistance of water flow.
6.3 The hygiene requirements for the epoxy resin or paint used for the anti-corrosion treatment of the valve body must be based on the test reports issued by relevant authoritative institutions. The chemical and physical properties should also comply with the specified requirements.
7. Valve packaging and transportation
7.1 Lightweight blocking plates should be installed on both sides of the valve for sealing.
7.2 For medium and small-sized valves, they should be tied with straw ropes and transported in container form.
7.3 For large-diameter valves, there is also a simple wooden frame for solid packaging to prevent damage during transportation.
8. Factory manual of the valve. As a piece of equipment, the following relevant data should be indicated in the factory manual of the valve: valve specification; model; working pressure; manufacturing standard; valve body material; valve stem material; sealing material; valve shaft packing material; valve stem sleeve material; internal and external anti-corrosion material; operation and start direction; rotation speed; opening and closing torque under working pressure conditions; manufacturer's name; date of manufacture; factory serial number; weight; diameter, number of holes, and center hole distance of the connecting flange; indicate the control dimensions of the overall length, width, and height in a graphical manner; valve flow resistance coefficient; effective opening and closing times; relevant data of valve factory inspection and installation and maintenance precautions, etc.