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A few precautions when purchasing valves

by:Sino Valves     2021-11-07
The following are some points of attention summarized when purchasing valves, which are only provided to manufacturers in need for reference and reference.   1. Variable speed gearbox:   1. The material of the box and the internal and external anti-corrosion requirements are consistent with the valve body principle.  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, its adjusting nut should be inside the box body.  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 will not cause separation and slippage when opening and closing with load.  5. The seal of the variable-speed transmission box and the valve shaft cannot be connected into a leak-free whole.   6. There is no debris in the box, and the gear bite part should be protected by grease.   2. Valve material:    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. Stem material: Strive for stainless steel stem (2CR13). Large-diameter valves should also be stainless steel embedded stems.  3. Nut material: use cast aluminum brass or cast aluminum bronze, and the hardness and strength are greater than the valve stem.  4. Stem bushing material: its hardness and strength should not be greater than that of the valve stem, and it will not form electrochemical corrosion with the valve stem and valve body under water immersion. 5. Material of sealing surface:   ①Different valve types, different sealing methods and material requirements;   ②Ordinary wedge gate valve, copper ring material, fixing method, and grinding method should all be explained;   ③Soft sealing gate valve, valve plate lining rubber Physical, chemical and sanitary testing data of materials;   ④Butterfly valves should indicate 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; usually Adopting nitrile rubber and EPDM rubber, etc., mixing with reclaimed rubber is strictly prohibited. 6. Valve shaft packing:   ①Because the valves in the pipe network are usually opened and closed infrequently, the packing is required to be inactive for several years, the packing is not aging, and the sealing effect is maintained for a long time;   ②The valve shaft packing should also be subjected to frequent openings. 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. 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 requires 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 the valve is closed. Working pressure value without leakage; 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.   Fourth, the operating mechanism of the valve:    1. When the valve is operated, the opening and closing direction should be closed clockwise.  2. Because 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. 3. In order to facilitate the opening and closing operation of one person, the maximum opening and closing torque should be 240m-m.   under the pressure of the pipeline. 4. The opening and closing operation end of the valve should be a square tenon, and the size should be standardized, and it should face the ground so that people can It can be operated directly from the ground. Valves with roulette are not suitable for underground pipe networks. 5. The display panel of the valve opening and closing degree ① The scale line of the valve opening and closing degree should be cast on the gearbox cover or on the shell of the display panel after changing the direction, all facing the ground, and the scale line is brushed with phosphor to show 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 Rivet lock.  6. u200bu200bIf the valve is buried deeply, and the operating mechanism and the display panel are 15m away from the ground, they should be equipped with extension rods, and they should be firmly fixed so that people can observe and operate from the ground. In other words, the opening and closing operations of valves in the pipe network are not suitable for downhole operations. V. Valve performance testing:   1. When a valve is manufactured in batches of a certain specification, an authoritative organization should be entrusted to perform the following performance testing:   ①The opening and closing torque of the valve under working pressure;   ②Under working pressure, the valve can be guaranteed Closed tightly the number of consecutive openings and closings;   ③The detection of the flow resistance coefficient of the valve in the pipeline water condition. 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 twice the valve working pressure;   ②When the valve is closed, both sides bear 11 times the valve working pressure. Value, no leakage; but the leakage value of the metal-sealed butterfly valve is not greater than the relevant requirements.  
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