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First, the introduction In the heating air conditioning water system, the valve is widely used to control water pressure, flow and flow. Second, the type of heating air-conditioning water system valves, structures and features Heating air-conditioning water system valves commonly used by the body structure and function can be divided into the interpretation of the valve, butterfly valve, globe valve, ball valve, plug valve, check valve, Pressure reducing valve, safety valve, steam trap, balance valve and so on. In accordance with the driving method is divided into manual, electric, hydraulic, pneumatic and other four ways. In accordance with the nominal pressure points high pressure, medium pressure, low pressure three categories. The working principle and characteristics of valves commonly used in heating and air conditioning water system are as follows: 1. Elucidation valve: Elucidation valve refers to the closing piece (elucidation) moves along the vertical axis of the media channel. The advantage is that the flow resistance coefficient is small, the torque required for opening and closing is small, and the medium flow direction is not limited. The disadvantage is the size of the structure, opening and closing a long time, sealing surface easily damaged, complex structure. Interpretation of the valve is divided into different types, the most common form of parallel and wedge-type valve, according to the structure of the valve stem can also be divided into Ming rod elucidation valve. (1) parallel-style interpretation of the valve refers to the two sealing surface parallel to the interpretation of the valve. For low pressure, medium and small diameter (DN50-400mm) of the pipeline. (2) Wedge-type interpretation valve refers to the two sealing surface into a wedge-shaped valve. Divided into two sets of board, a single board and elastic board. (3) Ming rod as the valve can be more intuitive display of the degree of opening and closing, so many years of small and medium diameter is widely used, usually less than or equal to 80mm DN Ming rod clarification valve. (4) dark rod elucidation of its stem nut in the valve body and the media in direct contact. For large-diameter valves and installation space is limited by the pipeline, such as underground pipelines. 2 butterfly valve its name comes from the wings of the butterfly structure. In the pipeline it is mainly used for cutting and throttling, when the butterfly valve is used to cut off, the use of flexible seal, the material selected rubber, plastic, etc., when used for throttling, the use of metal seal. Butterfly valve has the advantages of small size, light weight, simple structure, quick opening and closing, regulation and sealing performance is good, fluid resistance and operating torque smaller. According to the structure of the butterfly valve can be divided into lever (double rocker), center symmetry gate, offset plate and inclined plate. On the nominal diameter of DN <800mm butterfly valve should choose to bias plate. 3. Cut-off valve means the valve closing body (valve flap) moves along the centerline of the valve seat. It is generally only used in the pipeline cut off, but not for throttling, usually nominal diameter are limited to DN250mm below. The disadvantage is the pressure loss. Many kinds of globe valves, according to the structure is generally divided into straight-through, and DC-type. Angle valve in the refrigeration system is more used, the inlet channel was 90 degrees at right angles, will produce pressure drop, the biggest advantage is installed in the corner of the piping system, both 90-degree bend, but also easy to operate. 4. Ball Valve Ball valve is evolved from the plug valve, which is mainly used in the pipeline to cut off, distribute and change the media flow. It is characterized by the smallest fluid resistance, the same coefficient of resistance with the same length of the pipe, opening and closing fast, reliable sealing, compact structure, easy operation and maintenance, which are widely used in many occasions. Ball valve according to the structure of the ball can be divided into the following three types: (1) floating ball valve its simple structure, good sealing performance, due to the ball bearing the working medium load all transmitted to the outlet valve seat ring, so this structure Only suitable for medium and low voltage occasions, the disadvantage is the assembly difficulties, high precision requirements, while operating torque is also large. (2) Fixed ball valve Ball valve ball fixed by the two fixed together with the ball shaft support, under the media pressure, the ball will not produce displacement. It is suitable for high pressure and large diameter pipe. (3) flexible ball valve for high temperature, high pressure medium. There is an elastic groove on the ball body, this structure can reduce the friction between the two sealing surfaces when opening and closing, and also reduce the operating torque. 5. Plug Valve An important feature of the plug valve is that it is easy to adapt to a multi-channel structure so that one valve can obtain two, three or even four different flow paths. Many types of cocks, generally can be divided into: (1) tight set is generally used for PN less than or equal 0.6MPa occasions. (2) a large number of packing for the nominal pressure PN> 1.0MPa occasions. (3) self-styled mainly by the media itself to achieve the pressure, used for air media. Spring below the self-sealing structure can play the role of pre-tensioning and compression. In addition there are three links, four-way plug valves, and more for distribution, commutation and so on. 6. Check valve, also known as counter-flow valve, check valve, back pressure valve and check valve. Is a valve used to prevent backflow of media in pipes and equipment that automatically opens and closes by the force generated by the flow of the medium itself in the pipe. Swing type valve back to the valve seat around the valve seat rotation, but also sub-single and multi-valve, the former generally used for nominal diameter DN50-500mm, which is generally used for nominal diameter DN greater than or equal to 600mm. There are empty row check valve is used for boiler feed pump outlet to prevent media backflow and emptying from the role of the new slow closing check valve, eliminating the role of water hammer; diaphragm check valve to prevent water hammer performance is good; Ball check valve, is to prevent the reverse flow of the ideal product. 7. Reducing valve is through the throttling valve throttling and regulation, the media pressure is reduced, and through the valve after the direct effect of media pressure, the pressure after the valve automatically meet the predetermined requirements. Pressure P2 after the valve is usually less than the pressure before the valve P1 0.5 times, that is P2> 0.5P1. Pressure relief valve according to the structure is divided into piston, film, bellows, spring film type, lever spring type. 8. Safety valve It acts as a safety device on equipment, fittings and piping to prevent the pressure of the medium from exceeding the specified value. The main structure of the safety valve lever, spring and pilot (pulse) three. The advantage is small size, light weight. Sensitivity, the installation position is not limited; the disadvantage is that the force acting on the stem changes with the spring deformation. Spring-loaded safety valve is divided into micro-and full-Kai, with a wrench and without a wrench, closed and open different types. 9. Traps Traps for steam heating equipment and pipes to automatically exclude condensate, air and other non-condensable gases, and to prevent the loss of steam, which play a role in blocking the drainage of water vapor. Selection, the first according to the maximum displacement of condensate and import and export of pressure differential selection, but also be amended, the correction factor of 1.5-4; followed by a reasonable installation. Steam trap by opening and closing the form can be divided into the following categories: (1) mechanical steam traps: from the condensate level change public drive opening and closing pieces. (2) Thermostatic steam traps: Driven by changes in condensate temperature. (3) Thermodynamic steam traps: change from the dynamic properties of condensate into the public drive valve. 10. Balancing valve Balancing valve is used in hydraulic network to measure and adjust to the design flow, and has the necessary measurement accuracy of the valve. Third, the heating air conditioning water system valve selection reference points 1. Gate valve, globe valve and butterfly valve characteristics and selection (1) Gate valve body length is moderate, dial-style adjustment lever, adjust the performance, in the larger diameter pipe Is widely used. (2) Cut-off valve body length, dial-type adjustment lever, adjust the performance of good, suitable for spacious venues, small diameter of the occasion (usually DN less than or equal to 150mm). (3) butterfly valve body is short, handle-type lever, adjust the performance of slightly worse, higher prices, but the adjustment is easy, suitable for small venues, large diameter of the occasion (usually DN> 150mm). 2. Chiller, Heat Exchanger import and export, main pipeline regulation, can be selected according to the situation gate valve, globe valve or butterfly valve. 3. points, catchment, as the main function is to adjust, the general election stop valve or gate valve. 4. Pump inlet valve installed, the outlet installed two valves. The outlet side of the valve near the pump side check valve, the other two valves can choose gate valve, globe valve or butterfly valve. 5. Heating and air conditioning end of the device exit and exit of small-diameter pipe can choose the globe valve or ball valve. 6. Multi-storey, high-rise buildings on all levels of pipe can be semi-balanced valve installed to balance the flow of all levels. 7. Tanks and pipes, the lowest point of the device installed sewage valve, because it is not used for regulation, should be able to choose close the valve, such as gate valves, globe valves and so on. 8. Steam-condensate piping systems, such as steam heating systems, boiler water systems, steam lithium bromide chillers, steam-water heat exchanger systems, are typically equipped with pressure relief valves at the steam inlets; Set safety valve; condensate condensate at the installation of trap. 9. Heating air conditioning water system on the exhaust valve generally plug valves.