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What do you need to know when purchasing a valve?

放大word体  缩小word体 Release date:2018-12-10  来源:China Hydraulic parts net  作者:China Hydraulic parts net  Views:25
Core Tip:What do you need to know when purchasing a valve?1. The place of use and use of the valve: In the important position of the pressure pipeline, the general high-grade pressure pipeline, from the smelting process of the material to the inspection of the fin
      What do you need to know when purchasing a valve?

      1. The place of use and use of the valve: In the important position of the pressure pipeline, the general high-grade pressure pipeline, from the smelting process of the material to the inspection of the final product, is more demanding than the low-grade pressure pipeline.

      2. Confirm the working conditions of the valve, applicable medium, working pressure, and medium temperature:

      The corrosion resistance of different materials to the same corrosive medium is not the same. The temperature change often causes a series of performance changes of the material, such as the brittleness of the material at low temperature, the graphitization and creep of the material at high temperature, many corrosion. Forms are closely related to the temperature of the medium.

      3. Confirm the nominal diameter matching the pipe: DN (mm), NPS ( " )

      Confirm the connection with the pipeline: flange type, inner (outer) thread type, welded type, clip type, clamp type, ferrule type, etc.

      Confirm the driving mode of valve operation: manual, worm gear drive, pneumatic, electric, hydraulic electromagnetic, electro-hydraulic linkage.

      4. Confirm the type of valve: gate valve, globe valve, throttle valve, plunger valve, ball valve, butterfly valve, diaphragm valve, check valve, safety valve, trap, pressure reducing valve and other special valves.

      5. Confirm the use of the valve: switch type, adjustment type, safety type, etc.

      6. Confirm the material of the valve housing and internal parts: carbon steel, alloy steel, stainless steel, ductile iron, gray cast iron, copper alloy, aluminum alloy, plastic, etc.

      7. Confirm the sealing performance requirements, sealing level or seal leakage of the valve;

      8. Confirm the protective coating requirements, packaging requirements and transportation requirements of the valve;

      9. Specially required valves should also confirm: structural length, valve height, external dimensions, flow resistance, discharge capacity, flow characteristics, protection level, explosion-proof performance and other parameters;

      When the valve is purchased, only the traditional practices of specifying specifications, categories, and pressures to meet the procurement requirements are not perfect in the current market economy environment. Because valve manufacturers have formed their own corporate standards and product personality for product competition. Therefore, the valve purchaser puts forward the technical requirements in detail when purchasing the valve, and obtains a consensus with the valve manufacturer, which is necessary as an annex to the valve procurement contract.

      First, the general requirements for purchasing valves

      1. Valve specifications and categories should meet the requirements of the pipeline design documents.

      2. The model number of the valve should be numbered. If it is an enterprise standard, the relevant description of the model number 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 of the valve should be greater than the actual working pressure of the pipeline; any side under the closed condition of the valve should be able to withstand 1.1 times the working of the valve. The pressure value does not leak; the valve body should be able to withstand twice the working pressure of the valve when the valve is open.

      4. The valve manufacturing standard number should be marked. If it is an enterprise standard, the company's documents should be attached to the procurement contract.

      Second, the valve material

      1, the valve body material, and indicate the valve body material grade and the actual physical and chemical detection data.

      2, valve stem material, and strive for stainless steel valve stem, large diameter valve should also be stainless steel embedded valve stem.

      3, nut material, 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 be no more than the valve stem, and it will not form electrochemical corrosion with the valve stem and valve body under water immersion conditions.

      Third, the material of the sealing surface

      1The valve type is different, the sealing method and material requirements are different; 2 ordinary wedge type gate valve, the material, fixing method and grinding method of the copper ring should be explained; 3 soft sealing gate valve, physical and chemical inspection of the valve plate lining material Data; 4 butterfly valve should indicate the material of the sealing surface on the valve body and the sealing surface material on the butterfly plate; their physical and chemical testing data, especially the hygienic requirements of rubber, anti-aging performance, wear resistance; usually using nitrile rubber and ternary Ethylene-propylene rubber, etc., it is forbidden to use recycled rubber.

      Fourth, valve shaft packing

      1 Due to the valve in the pipe network, the opening and closing is usually infrequent, the filler is required to be inactive for several years, the filler is not aging, 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 sealing effect Goodness; 3 In view of the above requirements, the valve shaft packing should not 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 to replace it under water pressure.

      Five, 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 should have sealing measures. After the box is assembled, it can withstand the immersion of 3 meters of water column.

      3, the opening and closing limit device on the box, the adjusting nut should be inside the box or outside the box, but special tools are required to work.

      4, the transmission structure design is reasonable, can only drive the valve shaft to rotate when opening and closing, do not make it up and down, the transmission parts bite the appropriate degree, does not produce separation and slip when the load is opened and closed.

      5. The variable speed transmission box and the valve shaft seal cannot be connected to the whole without leakage. Otherwise, there should be reliable anti-leakage measures.

      6. There is no debris in the box, and the gear bite should be protected by grease.

      Sixth, the actuator of the valve

      1. The opening and closing direction of the valve should be closed clockwise.

      2, due to the valve in the pipe network, often manual opening and closing, the number of opening and closing rotation should not be too much, that is, the large diameter valve should also be within 200-600 rpm.

      3. In order to facilitate the opening and closing operation of a person, the maximum opening and closing torque should be 240N-m under the condition of pipeline pressure.

      4, the valve opening and closing operation end should be square, and the size is standardized, and facing the ground, so that people can directly operate from the ground. Valves with discs are not suitable for underground pipe networks.

      5, the degree of opening and closing of the valve display dial 1 valve opening and closing degree of the scale line, should be cast on the gearbox cover or the direction of the display panel after the conversion of the shell, always face the ground, the scale line is brushed with phosphor to show striking 2 indicates that the material of the disc needle can be used in the case of better management. Stainless steel plate is used. Otherwise, the painted steel plate should not be made of aluminum. 3 indicates that the disc needle is conspicuous and firmly fixed. Once the opening and closing adjustment is accurate, it should be Rivets are locked.

      6. If the valve is buried deep, the operating mechanism and the display panel are ≥1.5m away from the ground, and the extension rod facilities should be provided, and the fixing is stable so that people can observe and operate from the ground, that is, the valves in the pipe network. Opening and closing operations are not suitable for downhole operations.

      Seven, the performance test of the valve

      1. When a certain specification of a valve is manufactured in batches, an authoritative organization or a third-party inspection agency shall be entrusted to carry out the following performance tests: 1 the opening and closing torque of the valve under the working pressure condition; 2 under the working pressure condition, the valve can be closed tightly. The number of consecutive opening and closing times; 3 the detection of the flow resistance coefficient of the valve under the condition of pipeline water delivery.

      2, the valve should be tested before leaving the factory: 1 valve in the open condition, the valve body should withstand the internal pressure of the valve pressure value twice; 2 valve closed condition, the two sides respectively withstand 1.1 times the valve pressure Value, no leakage; but the metal-sealed butterfly valve, the leakage value is not greater than the relevant requirements.

      Eight, valve anti-corrosion treatment

      1. Inside and outside the valve body (including the variable speed transmission box), firstly, the shot blasting should be used to remove rust, and the electrostatic spraying powder-like non-toxic epoxy resin should be used to achieve a thickness of 0.3 mm or more. When a large valve is electrostatically sprayed with a non-toxic epoxy resin, it should be brushed and sprayed with a similar non-toxic epoxy paint.

       2. The interior of the valve body and the various parts of the valve plate require comprehensive anti-corrosion. On the one hand, it will not rust 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.

       3, the hygienic requirements of anti-corrosion epoxy resin or paint in the valve body, there should be a test report from the corresponding authority. Chemical and physical properties should also meet the relevant requirements.

      Nine, valve packaging and transportation

      1. Both sides of the valve should be provided with valve cover or light blockage for solid sealing.

      2. Medium-diameter valves and small-diameter valves should be bundled with straw ropes and transported by container.

      3, large-diameter valves also have a simple wooden frame solid packaging, so as not to damage during transportation.

      X. Valve manual and factory certificate

      The valve is the equipment. The following relevant data should be indicated in the valve's manual and factory certificate: valve specification; model; working pressure; manufacturing standard; valve body material; stem material; sealing material; valve shaft packing material; stem bushing material Internal and external anti-corrosion material; operation starting direction; number of revolutions; opening and closing torque under working pressure; manufacturer name; date of manufacture; factory number; weight; aperture of the connecting flange, number of holes, center hole distance; The method indicates the overall length, width and height of the control size; valve flow resistance coefficient; effective opening and closing times; relevant data of the factory inspection of the valve and precautions for installation and maintenance.

      Readers who read here hope that this article from Xiaobian can bring you a new understanding. If you want more hydraulic information, please continue to pay attention to China Hydraulic Parts Network and China Hydraulic Parts Mall. Xiaobian also updates the relevant information of hydraulic components everyday. If you have any suggestions to us, we will make corresponding supplement and optimization to the content according to your opinions, please support us more!
 
 
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