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8 main technical factors that need to be considered when purchasing valves

by:Sino Valves     2021-02-26
The practice of only clarifying specifications, categories, and pressures when purchasing valves to meet the procurement requirements is imperfect in the current market economy environment. For the purpose of product competition, valve manufacturers have carried out different innovations under the concept of unified valve design, forming their own corporate standards and product personality. Therefore, it is necessary to make detailed technical requirements when purchasing valves, and coordinate with manufacturers to reach a consensus, which is very necessary as an attachment to the valve procurement contract. 1. General requirements 1.1 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 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 national standard number on which it is based. If it is a corporate standard, the purchase contract should be accompanied by corporate documents. 2. Standard quality of the valve 2.1 The material of the valve body shall be mainly ductile iron, and the grade and actual physical and chemical test data of the cast iron shall be indicated. 2.2 Stem material, strive for 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 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 will 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 methods and material requirements are different; ②Common wedge gate valves, copper ring materials, fixing methods, and grinding methods should all be explained; ③Soft sealing gate valves, valve plate lining materials Physicochemical and hygienic testing data; ④Butterfly valves should be marked with the sealing surface material on the valve body and the sealing surface material on the butterfly plate; their physical and chemical testing data, especially the hygienic requirements, anti-aging performance, and wear resistance of rubber; It is strictly forbidden to mix reclaimed rubber with clear 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, the packing does not age, and the sealing effect is maintained for a long time; ② The valve shaft packing should also be subjected to frequent opening and closing , The goodness of the sealing effect; 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 the 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 principle. 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 For the opening and closing limit device on the box body, the adjusting nut should be inside or outside the box, but special tools are required for operation. 3.4 The design of the transmission structure is reasonable. It can only drive the valve shaft to rotate when opening and closing, without causing it to move up and down, and the transmission parts will bite properly and will not cause separation and slippage when opening and closing with load. 3.5 The variable-speed transmission box body and the valve shaft seal cannot be connected into a leak-free whole, otherwise there should be reliable leakage prevention measures. 3.6 There is no debris in the box, and the gear bite part should be protected by grease. 4. The operating mechanism of the valve 4.1 The opening and closing direction of the valve should always be closed clockwise. 4.2 Since the valves in the pipe network are often opened and closed manually, the number of opening and closing revolutions should not be too much, even for large-diameter valves, it should be within 200-600 revolutions. 4.3 In order to facilitate the opening and closing operation of one person, the maximum opening and closing torque should be 240N-m under the pipeline pressure condition. 4.4 The opening and closing end of the valve should be a square tenon, with standardized dimensions, and face the ground so that people can directly operate it from the ground. Valves with roulette are not suitable for underground pipe networks. 4.5 Display panel of valve opening and closing degree ①The scale line of 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 face to the ground, and the scale line should be painted with phosphor to show eye-catching; ②The material of the indicator dial needle can be made of stainless steel plate under the condition of good management, otherwise it is painted steel plate, do not use aluminum skin; ③The indicator dial needle is eye-catching and fixed firmly. Once the opening and closing adjustment is accurate, rivets should be used locking. 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, it should be equipped with an extension rod facility, and it should be firmly fixed so that people can observe and operate from the ground. In other words, the opening and closing of valves in the pipe network is not suitable for downhole operations. 5. Valve performance testing 5.1 When a valve of a certain specification is 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, the valve can be closed tightly The number of continuous opening and closing times; ③The detection of the flow resistance coefficient of the valve under the condition of pipeline water delivery. 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 of twice the valve working pressure; ②When the valve is closed, both sides bear 1.1 times the valve working pressure. , No leakage; but the leakage value of the metal-sealed butterfly valve is not greater than the relevant requirements.
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