Do you know What Factors Need to be Considered in the Valve Procurement Process?(Part 1)
- KEPLER TEAM
- Dec 16, 2021
- 4 min read
The practice of only clarifying the specifications, categories, and pressures when purchasing valves to meet the procurement requirements is imperfect in the current market economy environment. Because the valve manufacturers have made different innovations under the concept of unified valve design for product competition, forming their own corporate standards and product personality. Therefore, it is necessary to make detailed technical requirements when purchasing valves, and coordinate with the manufacturers to reach a consensus, which is very necessary as an attachment to the valve procurement contract.
1. General requirements
(1) The valve specifications and categories should meet the requirements of the pipeline design documents.
(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.
(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 valve when it is closed. The working pressure value does not leak; when the valve is open, the valve body should be able to withstand twice the valve working pressure.
(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. Valve standard quality
(1) The material of the valve body should be mainly ductile iron, and the grade and actual physical and chemical test data of the cast iron should be indicated.
(2) Stem material, strive for stainless steel stem (2CR13), large diameter valves should also be stainless steel embedded stems.
(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.
(4) The material of the valve stem bushing should have a hardness and strength not greater than that of the valve stem, and it should not form electrochemical corrosion with the valve stem and valve body under water immersion.
(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 rubber Material physicochemical and hygienic testing data; ④Butterfly valves 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 Adopting nitrile rubber and EPDM rubber, etc., mixing with reclaimed rubber is strictly prohibited.
(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 does not age, 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
(1) The material of the box body and the internal and external anti-corrosion requirements are consistent with the principle of the valve body.
(2) The box body should have sealing measures, and the box body can withstand 3 meters of water column immersion after assembly.
(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.
(4) The design of the transmission structure is reasonable. It can only drive the valve shaft to rotate when opening and closing, without making it move up and down, and the transmission parts will bite properly, and there will be no separation and slippage when opening and closing with load.
(5) The variable-speed transmission box body and the valve shaft seal should not be connected as a leak-free whole, otherwise reliable leakage prevention measures should be taken.
(6) There is no debris in the box, and the gear bite part should be protected by grease.
4. Valve operating mechanism
(1) The opening and closing direction of the valve should always be closed clockwise.
(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 the large-diameter valves should also be within 200-600 revolutions.
(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) 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.
(5) Display panel of valve opening and closing degree ① The 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. Eye-catching; ②The material of the indicator disc needle can be made of stainless steel under the condition of good management, otherwise it is painted steel plate, do not use aluminum skin; ③The indicator disc needle is eye-catching and fixed firmly. Once the opening and closing adjustment is accurate, it should be Lock with rivets.
(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 should be provided, and it should 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.
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