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   Butterfly valve is one of the valves commonly used in water supply pipelines. Butterfly valves have the common problems of opening and closing laborious and time-consuming, corrosion, cracking, poor sealing, and cannot quickly dispose of pipe bursts and other emergencies, encountered in these cases can only be helpless to dismantle the well to change the valve and then masonry maintenance, costly and time-consuming.so the selection of butterfly valve should pay attention to the following aspects.

   1、Choose to open and close the energy-saving materials and structures

   (1) Shaft system material. The shaft system contains the upper and lower valve shafts in the valve body part and the gear shaft and worm gear in the gearbox. Ideal shaft material is martensitic stainless steel 2Cr13, through the tempering and quenching treatment, with a certain degree of hardness, strength, stiffness, corrosion resistance, not easy to bend and deformation.

   (2) For the valve stem rust dead, can choose a smaller friction coefficient of self-lubricating bearings, multi-channel sealing ring and improve the material to solve.

   (3) The structural design of the shaft system should be reasonable. The upper sleeve and the butterfly plate are connected by pins, the lower valve shaft is fixedly connected with the valve body and the butterfly plate is in relative motion: the spacing between the butterfly plate and the axial support is greatly shortened, the deformation and displacement of the butterfly plate are controlled in the minimum state when it is pressurised, and the change of the specific pressure of the sealing surface is not too big. Therefore, the valve opens and closes with less effort.

    2、The choice of opening and closing time-saving operating mechanism

   (1) Valve manual drive device set up a two-stage deceleration mechanism, the total input torque are not more than 200N-m can open the valve, the first stage for the worm gear deceleration mechanism.

 （2）Valve actuator self-locking, in the valve plate fully open and fully closed between any position of operation and static will not produce creep and chatter. Valve operating mechanism has enough rigidity, strength, enough to withstand the opening and closing torque of the valve, to ensure the stability of the valve plate opening and closing.

    3、Select efficient valve body corrosion of the coating process

    (1) Pre-painting treatment. Valve body, valve plate and other castings using resin sand moulding process, before painting, the castings should be treated by shot blasting and painted within 6h after completion.

   (2) Spraying and Warranty. Electrostatic spraying epoxy powder process, the coating does not dissolve in water after curing, the coating thickness is ≥300μm, and there is an insulating property of 3kV voltage resistance. The coating adopts epoxy powder coating with WRAS certificate.

   4、The selection of high-strength valve body castings and structures

   (1) The butterfly valve should be a fully cast two-way sealed butterfly valve. All cast butterfly valve relative to the advantages of welded butterfly valve is: all cast valve body, valve plate itself, corrosion resistance, abrasion resistance, resistance to pressure and vibration and deformation resistance is far better than the steel plate welded valve body, valve plate.

   (2) Connection of valve shaft and valve plate. The valve stem adopts half shaft, and the length embedded in the shaft hole is not less than 1.5 times of the shaft diameter. The valve plate adopts truss structure, featuring high compressive strength, good flow conductivity, small flow resistance, large overflow area and energy saving. The connection between the valve shaft and the valve plate adopts cone pin connection and proprietary expansion pin connection. This structure can effectively eliminate the gap between the valve spindle and the butterfly plate and has strong anti-pressure, twisting and anti-loosening performance, reliable opening and closing.

    5、Select the structure with reliable sealing

  (1) It has positive and negative two-way sealing function. Installation is not limited by the direction of media flow, and is not affected by the space position, can be installed in any direction.

  (2) Adopt double eccentric structure. When closing the valve plate sealing surface with the eccentric displacement to the valve body sealing ring extrusion sealing, sealing ring pressure uniformity, sealing performance is reliable; open the valve plate only need to turn a very small angle, the valve plate sealing surface and the valve body sealing ring detached from the reduction of friction between the sealing surface, so that the valve is durable and save time and effort!

   (3) Improved sealing structure. Valve body valve plate body material for ductile cast iron, valve plate sealing parts with stainless steel 1Cr18Ni9Ti double bread welding, after processing after rolling polishing, surface organisation dense and hardness has been improved, the valve body sealing ring is fixed mechanically in the valve body, using the same kind of stainless steel machining surface for nitriding treatment, by the process measures to ensure that the sealing vice has HRC8 ~ 20 hardness difference, which will effectively extend the This will effectively extend the service life, and has a very good anti-scaling and sealing self-cleaning ability.

    (4) Each butterfly valve factory should be positive and reverse hydraulic sealing test (1.1 times the nominal pressure), sealing are up to the relevant standard requirements, and show a detailed inspection, test records and complete test reports.

     6、Select the structure with reliable sealing of open and close drive system.

   (1) The design of the valve's shaft sleeve and shaft system seal. Valve shaft sleeve using self-lubricating bearings, friction coefficient is small, the upper valve shaft sealing using two self-compensating seals, the material is NBR. lower valve shaft sealing using O-ring sealing, high reliability and easy to replace. In order to avoid the media impurities into the sleeve, in the upper and lower valve shaft sleeve end face to add an anti-sand O-ring seal.

    (2) sealing design of worm gear box: all the moving parts and fixed connection parts of the worm gear box that are connected to the outside are designed with sealing elements, and the box is filled with grease or oil, so that it can be applied to dusty, humid and other harsh environments and can be immersed in 3m of deep water for long term use, and the protection level is up to IP68, and the inspection report of the worm gear drive device should be provided.

    7、Optional electric actuator

Electric actuator as an option, should meet: the use of special sealed motor, waterproof grade up to standard, insulation class F; valve opening and closing positions are set up to limit the mechanism, and set up overload protection mechanism; set up the valve opening in situ position indication and remote dynamic display mechanism, with the opening of the feedback output (using the 4 ~ 20mA current); with the switching control, in place of the contact, the above contact wiring leads should meet the local and remote Control requirements (DCS control requirements); the use of integrated electrical equipment, electrical components are concentrated in the electrical equipment, with remote control, valve position signals (open in place, close in place more than two groups) and other contacts.

    The above selection of butterfly valves involves technologies, techniques and materials with high scientific and technological content and good comprehensive performance, so that the butterfly valve has good sealing effect in the pipeline network, long service time, flexible operation, easy replacement and simple maintenance, which can greatly ensure the complete and stable operation of the pipeline network.

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