What are the applicable occasions for various valves?

General requirements: According to the characteristics of each product's production process and various media, the general requirements for valve selection are as follows:: Article 1: The first principle of valve selection is that the sealing performance of the valve must meet the requirements of the medium. That is, internal leakage must comply with the standard GB/T13927-1992 "General Valve Pressure Test", while external leakage is not allowed at all. Article 2: Choose the correct type of valve. The correct selection of valve type is prerequisite for the user to comprehensively estimate the needs of the entire production process. When selecting the valve type, the user should first understand the structural characteristics and performance of each valve. General valve type selection: For example, for medium and low pressure steam, use a stop valve with a copper sealing surface, and for steam above DN200, use a gate valve. ； Butterfly valves are used on the main circulating water pipes, and rubber-lined gate valves are used on the branch pipes. ； Butterfly valves are used on the low-pressure air main pipes and stop valves are used on the branch pipes. ； Generally, ball valves are used for liquid materials. Article 3: Determine the end connections of the valve. Among threaded connections, flange connections, and welded end connections, the first two are the most commonly used. Among them, the price of the threaded connection form is much lower than the flange connection form. Generally, it is a smaller diameter valve and should be selected first. Article 4: Selection of materials for the main parts of the valve. When selecting the material of the main parts of the valve, you should first consider the physical properties (temperature, pressure) and chemical properties (corrosiveness) of the working medium. You should also know how clean the media is (whether there are solid particles). In addition, it is also necessary to refer to * * and the relevant regulations of the user department. Correct and reasonable selection of valve materials can achieve the most economical service life and best performance of the valve. (Appendix Table 1-1, 1-2, 1-3) The selection order of valve body materials is roughly in the order of cast iron-carbon steel-stainless steel, and the selection order of sealing ring materials: Rubber-Copper-Alloy Steel-F4. Article 5: Determine the flow rate through the valve. Article 6: Pressure levels are selected in order from low to high. The selection standards and requirements for various types of valves are as follows:: Gate valve characteristics: Good sealing performance, small fluid resistance, and certain adjustment performance ； However, it is large in size, complex in structure, difficult to process, easy to wear on the sealing surface, difficult to maintain, and takes a long time to open and close. It is suitable for making large-diameter valves. In addition to being suitable for steam, oil and other media, it is also suitable for media containing granular solids and high viscosity. It is also suitable for valves in venting and low vacuum systems. Selection criteria: Flat gate valve 1. Applicable medium range: Water, steam, oil, oxidizing corrosive media (Z42W-16Ti), acid, alkali flue gas, etc. 2. The gate valve is suitable for steam, high-temperature oil, oil and gas and other media, as well as parts with frequent opening and closing. It is not suitable for media that are prone to coking. ； 3. City gas transmission pipelines use single-gate or double-gate soft-sealed open-stem flat gate valves. ； 4. For urban water supply projects, single or double gate open-stem flat gate valves without diversion holes should be selected. ； 5. For pipelines with suspended particle media, use knife-shaped flat gate valves ； Wedge gate valve 1. Generally only suitable for fully opening or fully closing, and cannot be used for adjustment and throttling. ； 2. Generally used in situations where there are no strict requirements on the external dimensions of the valve and the use conditions are relatively harsh. For example, when working media with high temperature and high pressure require the closing parts to ensure long-term sealing, etc. ； 3. Generally, wedge gate valves are recommended when using conditions or requiring reliable sealing performance, high pressure, high pressure cut-off, low pressure cut-off, low noise, cavitation and vaporization phenomena, high temperature media, and low temperature and cryogenic temperatures. Such as petrochemical oil, water supply projects and sewage treatment projects in urban construction, chemical industry and other fields. ； 4. Use it in working conditions that require small flow resistance, strong flow capacity, good flow characteristics, and strict sealing. ； 5. Use wedge gate valves for high temperature and high pressure media ； Such as high temperature steam, high temperature and high pressure oil products. 6. Low temperature and cryogenic media such as: Liquid ammonia, liquid hydrogen, liquid oxygen, etc. use wedge gate valves ； 7. For low-pressure and large-diameter applications, such as water supply projects and sewage treatment projects, wedge gate valves are used ； 8. When the height is restricted, use the concealed stem type. When the installation height is not restricted, use the rising stem gate valve. ； 9. In situations where the frequency of opening and closing is low, wedge gate valves should be used ； 10. The wedge-type single-gate gate valve is suitable for high-temperature media that are prone to coking. The wedge-type double-gate gate valve is suitable for steam, oil, and media with greater wear on the sealing surface, or in locations with frequent switching. It is not suitable for media that is prone to coking. ； like: Z15T-10K, Z45T-10, Z45W-10, Z41T-10 : ≤100℃ circulating water and other media ； Z41H-16C, Z41H-25C: Suitable for steam, oil, etc. ； Z44H-16Q: ≤200℃ water vapor ； Z44H-25: ≤200℃ water vapor ； Z41H(Y)-40: ≤425℃ water, oil, steam ； Z44T(W)-10: ≤100℃ water vapor, oil. Globe valve features: The regulating performance is good, the sealing performance is not very good, the structure is simpler than the gate valve, the manufacturing and maintenance are more convenient than the gate valve, the fluid resistance is larger, and the price is cheaper than the gate valve. Selection criteria: 1. Stop valves should be used on pipelines or devices with high-temperature and high-pressure media. ； For example, it is appropriate to use stop valves on high-temperature and high-pressure pipelines in thermal power plants and petrochemical systems. ； 2. On pipelines where convection resistance requirements are not strict, that is, where pressure loss is not considered much ； 3. Stop valves can be used for small valves, such as needle valves, instrument valves, sampling valves, pressure gauge valves, etc. ； 4. There is flow adjustment or pressure adjustment, but the adjustment accuracy is not high, and the pipeline diameter is relatively small. For example, on pipelines with a nominal diameter ≤50mm, a stop valve or a throttle valve should be used. ； 5. In water supply and heating projects in urban construction, stop valves, balance valves or plunger valves can be used for pipelines with smaller nominal diameters, such as pipelines with nominal diameters less than 150mm. ； 6. Suitable for steam and other medium pipelines below DN200 ； 7. Not suitable for media with high viscosity ； 8. Not suitable for media containing particles that are prone to sedimentation. ； 9. It is not suitable to be used as a vent valve or a valve in a low vacuum system. For selection, please refer to Table 15-105 P3-126 in the second volume of "Chemical Process Manual". J41C-10C plunger valve features: Good sealing, compact structure, flexible door opening, long life and easy maintenance ； But the relative price is higher. Selection criteria: 1. It is required to be used in places with high sealing requirements. ； 2. Used on water, steam, oil (UJ41W-16 (25) C) nitric acid, acetic acid and other media (UJ41W-16 (25) P/R). . 3. See the second volume of "Chemical Process Manual", Table 15-177, P3-159. Ball valve features: It has a simple structure, quick opening and closing, easy operation, small size, light weight, few parts, minimal fluid resistance and good sealing performance. Selection criteria: 1. Suitable for low temperature (≤150℃), high pressure and high viscosity media ； 2. It cannot be used for flow adjustment. ； 3. Used in situations requiring quick opening and closing ； 4. Generally, ball valves are recommended for pipelines with double-position adjustment, strict sealing performance, wear, shrinkage channels, rapid opening and closing movements, high-pressure cutoff (large pressure difference), low noise, vaporization, small operating torque, and small fluid resistance. ； 5. Also suitable for light structures, low pressure cutoffs, and corrosive media ； 6. The most ideal valve for low-temperature and cryogenic media. For pipeline systems and devices with low-temperature media, cryogenic ball valves with a valve cover should be used. ； 7. Most ball valves can be used in media with suspended solid particles. Depending on the sealing material, they can also be used in powdery and granular media. ； 8. When selecting a floating ball valve, the valve seat material should withstand the full load of the ball and the working medium. Large-diameter ball valves require greater force during operation. Ball valves with a DN of 200mm or more should use worm gear transmission. ； 9. When selecting high-pressure and large-diameter ball valves (tank bottom valves with DN greater than 200mm), fixed ball valves should be used. ； 10. For corrosive media such as acid and alkali in chemical systems, it is appropriate to choose an all-stainless steel ball valve made of austenitic stainless steel and with polytetrafluoroethylene as the valve seat seal. 11. For selection, refer to Table 15-157 P3-149 in the second volume of the "Chemical Process Manual". Q1 (4) 1F-16 (25, 40) ≤ 150℃ water and oil ； Q41F-16C water and oil products ； Q41F-16P nitric acid, room temperature citric acid solution, lysine, organic acid ； Q41F-16R acetic acid, citric acid solution above 50℃. 12. General selection sequence: Q11F-16——Q41F-16PF——Q11F-16P——Q41F-16——Q41F-16PC——Q41F-16P——Q41F-16R—— Q41F46-16C (P, R) Throttle valve characteristics: It has small dimensions, light weight, good adjustment performance, but low adjustment accuracy. Due to the large flow rate, the sealing surface is easily eroded. Selection criteria: 1. Suitable for low temperature and pressure ； higher medium ； 2. Parts where flow and pressure need to be adjusted ； 3. Not suitable for media with high viscosity and solid particles. ； 4. Not suitable for use as isolation valve ； 5. Selection reference: "Chemical Process Manual" Volume 2 Table 15-106 P3-128 ； L21W (24W, 21B, 24B, 41B)-25K: Ammonia, liquid ammonia, (-40~150℃). Plug valve features: It has simple structure, quick opening and closing, easy operation, small fluid resistance, few parts and light weight. Selection criteria: 1. Generally not suitable for steam ； 2. Generally not suitable for medium with higher temperature ； 3. Used for media with lower temperature and high viscosity (water, oil, acidic media) ； 4. Used in situations requiring quick opening and closing ； 5. Mainly used for cutting off and connecting the medium, distributing the medium and changing the flow direction of the medium. ； 6. Depending on the nature of use and the erosion resistance of the sealing surface, it can sometimes be used in throttling situations. ； 7. Usually, media with suspended particles can also be used ； 8. Suitable for connecting and grounding ； 9. Suitable for multi-channel structures. One valve can obtain 2 to 4 different flow channels, which can reduce the amount of valves used. ； 10. It is used to distribute the medium and change the flow direction of the medium. Its working temperature is ≤300℃, the nominal pressure is ≤1.6Mpa, and the nominal diameter is ≤300mm. It is recommended to use a multi-channel cock. ； 11. For equipment and pipelines in milk, juice, beer and other food companies and pharmaceutical factories, it is recommended to use tight-set conical plug valves made of austenitic stainless steel. ； 12. In large chemical industries, where pipelines and equipment containing corrosive media require fast opening or closing speed, for nitric acid-based media, 1Cr18Ni9 stainless steel PTFE sleeve-sealed conical plug valves can be used ； For acetic acid-based media, a PTFE sleeve-sealed conical plug valve made of Cr18Ni12Mo2Ti stainless steel can be used ； 13. In pipelines and equipment of gas, natural gas, and HVAC systems, when the nominal pressure is ≤1.0Mpa and the nominal diameter is ≤200mm, it is advisable to use a packed conical plug valve. ； Butterfly valve characteristics: Small size, light weight, quick switch, and certain adjustment performance. Selection criteria: 1. Suitable for making valves with larger diameters (such as DN600 or above) ； 2. Butterfly valves should be used when the structural length is short. ； 3. It is not suitable to be used in high temperature and high pressure pipeline systems. It is generally used in: ≤80℃, ≤1.0Mpa crude oil, oil products, water and other media ； 4. Since the pressure loss of butterfly valves is relatively large compared to gate valves and ball valves, butterfly valves are suitable for pipeline systems with loose pressure loss requirements. ； 5. It is suitable to be used in pipelines that require flow adjustment. ； 6. Butterfly valves are suitable for applications that require fast opening and closing. ； 7. Generally, in throttling, regulating control and mud media, short structural length, fast opening and closing speed, and low pressure cutoff (small pressure difference) are required. Butterfly valves are recommended. ； 8. Butterfly valves can be used when there are double-position adjustments, narrowing channels, low noise, vaporization, a small amount of leakage to the atmosphere, and corrosive media. ； 9. When using butterfly valves under special working conditions such as throttling adjustment, strict sealing requirements, severe wear, low temperature (cryogenic), etc., a specially designed triple-eccentric or double-eccentric butterfly valve with a specially designed metal seal with an adjustment device is required. ； 10. The center line butterfly valve is suitable for fresh water, sewage, sea water, salt water, steam, natural gas, food, medicine, oil, various acid and alkali and other pipelines that require complete sealing, zero gas test leakage, high life requirements, and operating temperatures of -10 to 150°C. ； 11. The soft-sealing eccentric butterfly valve is suitable for two-way opening and closing adjustment of ventilation and dust removal pipelines. It is widely used in gas and water pipelines in metallurgy, light industry, electric power, and petrochemical systems. ； 12. Metal-to-metal wire sealed double eccentric butterfly valve is suitable for urban water supply, heating, steam supply and gas, oil, acid and alkali pipelines, etc., as a regulating and throttling device ； 13. In addition to being used as a program control valve for large-scale pressure swing adsorption (PSA) gas separation devices, the metal-to-metal wire-sealed triple eccentric butterfly valve can also be widely used in petroleum, petrochemical, chemical, metallurgy, electric power and other fields. It is a good substitute for gate valves and globe valves. ； 14. Selection reference: "Chemical Process Handbook" Volume 2 Table 15-193, P3-167. Check valve features: According to the structural form, it is divided into lifting type and swing type. Selection criteria: 1. In order to prevent medium backflow, check valves should be installed on equipment, devices and pipelines. ； 2. Check valves are generally suitable for clean media and are not suitable for media containing solid particles and high viscosity. ； 3. Generally, vertical lift check valves should be used on horizontal pipelines with a nominal diameter of 50mm. ； 4. The straight-through lift check valve can be installed on both horizontal and vertical pipelines. ； 5. For the water pump inlet pipeline, a bottom valve should be used. The bottom valve is generally only installed on the vertical pipe at the pump inlet, and the medium flows from bottom to top. ； 6. The lifting type has better sealing and greater fluid resistance than the swing type. The horizontal type should be installed on horizontal pipes, and the vertical type should be installed on vertical pipes. ； 7. The installation position of the swing check valve is not restricted. It can be installed on horizontal, vertical or inclined pipelines. If installed on a vertical pipeline, the medium flow direction must be from bottom to top. ； 8. Swing check valves should not be made into small-diameter valves. They can be made into very high working pressures, PN can reach 42MPa, and DN can also be made very large, with the maximum reaching more than 2000mm. Depending on the materials of the shell and seals, it can be applied to any working medium and any working temperature range. The medium is water, steam, gas, corrosive medium, oil, medicine, etc. The working temperature range of the medium is between -196~800℃ ； 9. The applicable occasion is low pressure and large diameter, and the installation occasion is limited. ； 10. The installation position of butterfly check valve is not restricted and can be installed on horizontal pipelines. It can also be installed on vertical or inclined pipelines. ； 11. The diaphragm check valve is suitable for pipelines prone to water hammer. The diaphragm can well eliminate the water hammer caused by the reverse flow of the medium. It is generally used on low-pressure and normal temperature pipelines, especially suitable for tap water pipelines. Generally, the working temperature of the medium is between -20 ~ 120°C, and the working pressure is <1.6MPa. However, the diaphragm check valve can be larger in diameter, and the maximum DN can reach more than 2000mm. ； 10. Ball check valve is suitable for medium and low pressure pipelines and can be made into large diameter ； 11. The shell material of the spherical check valve can be made of stainless steel, and the hollow sphere of the seal can be coated with polytetrafluoroethylene engineering plastic, so it can also be used in pipelines with general corrosive media. The operating temperature is between -101~150℃, its nominal pressure is ≤4.0MPa, and the nominal diameter range is between 200~1200 ； 12. When selecting a check valve for incompressible fluids, you must first evaluate the required closing speed. The second step is to select the type of check valve that may meet the required closing speed. ； 13. The check valve for compressible fluids can be selected in a similar way to the check valve for incompressible fluids. If the medium flow range is large, the check valve for compressible fluids can use a reduction device. If the medium flow stops and starts quickly, such as the outlet of a compressor, a lift check valve is used. ； 14. The check valve should be sized accordingly. The valve supplier must provide data on the selected size so that the valve size when the valve is fully open at a given flow rate can be found. ； 15. For high and medium pressure check valves below DN50mm, vertical lift check valves and straight-through lift check valves should be used ； 16. For low-pressure check valves below DN50mm, butterfly check valves, vertical lift check valves and diaphragm check valves should be used ； 17. For high and medium pressure check valves with DN greater than 50mm and less than 600mm, swing check valves should be used ； 18. For medium and low pressure check valves with a DN greater than 200mm and less than 1200mm, a wear-free spherical upper return valve should be used ； 19. For low-pressure check valves with DN greater than 50mm and less than 2000mm, butterfly check valves and diaphragm check valves should be used ； 20. For pipelines that require small or no water hammer when closing, slow-closing swing check valves and slow-closing butterfly check valves should be used. ； Diaphragm valve features: 1. No stuffing box required ； 2. Simple structure, good sealing performance, easy maintenance and low fluid resistance. Selection criteria: 1. Generally used on pipelines with DN≤200mm. ； 2. Suitable for media with T≤180℃ and ≤1.0Mpa ； 3. Generally used in corrosive media (acidic media, etc.) ； 4. The selection of diaphragm valve should be based on the pressure-temperature grade of the diaphragm valve. ； 6. For abrasive granular media, choose a weir-type diaphragm valve. When selecting a weir-type diaphragm valve, you must follow its flow characteristics table. ； 7. For viscous fluids, cement slurries and precipitating media, choose straight-through diaphragm valves ； 8. Except for specific varieties, diaphragm valves should not be used in vacuum pipelines and vacuum equipment. ； 9. Diaphragm valves should be used on equipment and pipelines produced in the food industry and medical and health industry. ； 10. Suitable for oil, water, acidic media and media containing suspended solids, not suitable for organic solvents and strongly oxidizing media ； 11. For various corrosive medium pipelines, the recommended lining materials and diaphragm materials for pipelines with DN ≤ 200mm and below, operating temperature ≤ 180°C, and Pn ≤ 1.6Mpa are as shown in the attached table (9-1, 9-2) ； 12. Selection reference: "Chemical Process Handbook" Volume 2 Table 15-205, P3-171. Steam trap selection standards: 1. Can accurately remove condensation water ； 2. No steam leakage ； 3. Ability to remove air ； 4. It can improve steam utilization, has good durability, wide back pressure tolerance, strong water hammer resistance, and allows maintenance. ； 5. The technical parameters of the trap, such as nominal pressure, maximum allowable temperature, maximum working pressure, minimum working pressure, maximum back pressure rate, condensate displacement, etc., should comply with the working conditions of the steam pipe network. ； 6. In the condensate recovery system, if working back pressure is used to recover condensate, a trap with a higher back pressure rate should be selected, such as a mechanical trap. ； 7. In the condensate recovery system, if the steam equipment is required to discharge both saturated condensate and non-condensable gas in a timely manner, a trap with dual functions of drainage and exhaust should be selected. ； 8. If the steam equipment is not allowed to accumulate condensate, a trap that can continuously discharge saturated condensate should be selected, such as a float-type trap. ； 9. When the working pressure of steam equipment fluctuates frequently, a trap that does not require adjustment of the working pressure should be selected. Selection and installation requirements: 1. Determine the pressure difference between the inlet and outlet of the steam trap according to the actual operating conditions. ； 2. According to the amount of condensation water that the steam heating equipment may produce during normal operation, multiply it by the selection correction coefficient K, and then select it based on the drainage volume of the steam trap. ； 3. Clean the pipeline equipment before installation to remove impurities to avoid blockage. ； 4. The steam trap should be installed under the steam equipment and in a place where drainage is easy to occur. ； 5. Steam traps should be installed in places that are easy to inspect and maintain, and arranged as centrally as possible to facilitate management. ； 6. Each steam heating equipment should be equipped with a separate steam trap. ； 7. The bypass pipe should not be installed lower than the steam trap ； 8. When installing, pay attention to the direction of the arrow on the valve body and the flow direction of the medium in the pipeline. ； 9. The medium flow direction at the inlet and outlet of the steam trap should have a downward slope of 4%, and the nominal diameter of the pipeline should not be smaller than the nominal diameter of the steam trap. ； 10. When the drainage capacity of one steam trap cannot meet the requirements, several steam traps can be installed in parallel. ； 11. When used in places where freezing may occur, anti-freeze measures must be taken ； 12. Install a cut-off valve at the outlet and inlet of the steam trap to facilitate maintenance and cleaning. ； 13. If the steam trap itself does not have an anti-reverse device, a check valve can be installed according to the specific situation. ； 14. Lead a bypass pipe at the outer end of the inlet and outlet stop valves to discharge a large amount of condensed water when the equipment is started. On equipment that must be operated, when the steam trap fails to repair, it can be slightly opened and temporarily used as a steam trap. ； 15. The flushing pipe, inspection pipe and bypass pipe should be closed tightly during normal operation and should be determined according to the specific use conditions. Try not to set them up to avoid a large amount of steam loss due to operating errors and failure to close in time. Safety valve selection standards: 1. Steam boiler safety valves generally use full-open spring safety valves. ； 2. For safety valves used for liquid media, micro-opening spring safety valves are generally used. ； 3. Safety production valves for air or other gas media generally use full-open spring-type safety valves. ； 4. Safety valves for LPG car tanks or LPG railway tank cars generally use full-open built-in safety valves. ； 5. The high-pressure bypass safety valve of steam power generation equipment generally uses a pilot-operated safety valve with dual functions of safety and control. Pressure reducing valve selection standards: 1. Within the given spring pressure level range, the outlet pressure can be continuously adjusted between the maximum value and the minimum value, and there must be no jamming or abnormal vibration. ； 2. For soft-sealed pressure reducing valves, there must be no leakage within the specified time. ； For metal-sealed pressure reducing valves, the leakage should not be greater than 0.5% of the maximum flow rate ； 3. When the outlet flow changes, the outlet pressure deviation of the direct-acting type shall not be greater than 20%, and that of the pilot-operated type shall not be greater than 10%. ； 4. When the inlet pressure changes, the outlet pressure deviation of the direct-acting type shall not be greater than 10%, and that of the pilot-operated type shall not be greater than 5%. ； 5. Generally, the pressure behind the pressure reducing valve should be less than 0.5 times the pressure in front of the valve. ； 6. Pressure reducing valves have a wide range of applications and can be used on equipment and pipelines for steam, compressed air, industrial gas, water, oil and many other liquid media. The amount of medium flowing through the outlet of the pressure reducing valve is generally expressed by mass flow or volume flow. ； 7. Bellows direct-acting pressure reducing valve is suitable for low-pressure, medium- and small-diameter steam media. ； 8. Diaphragm direct-acting pressure reducing valve is suitable for medium and low pressure, medium and small diameter air and water media. ； 9. Pilot piston type pressure reducing valve is suitable for steam, air and water media of various pressures, various calibers and various temperatures. If it is made of stainless acid-resistant steel, it can be suitable for various corrosive media. ； 10. Pilot bellows type pressure reducing valve, suitable for low pressure, medium and small diameter steam, air and other media ； 11. Pilot diaphragm pressure reducing valve, suitable for low pressure, medium pressure, medium and small diameter steam or water and other media ； 12. The fluctuation of the inlet pressure of the pressure reducing valve should be controlled between 80% and 105% of the given value of the inlet pressure. If it exceeds this range, the performance in the early stage of pressure reduction will be affected. ； 13. Usually the pressure behind the pressure reducing valve should be less than 0.5 times the pressure in front of the valve. ； 14. Each spring of the pressure reducing valve is only applicable within a certain outlet pressure range. If it exceeds the range, the spring should be replaced. ； 15. In situations where the working temperature of the medium is relatively high, pilot piston type pressure reducing valve or pilot bellows type pressure reducing valve is generally used. ； 16. When the medium is air or water (liquid), it is generally advisable to choose a direct-acting diaphragm pressure reducing valve or a pilot diaphragm pressure reducing valve. ； 17. When the medium is steam, a pilot piston type or pilot bellows type pressure reducing valve should be used. ； 18. For the convenience of operation, adjustment and maintenance, pressure reducing valves should generally be installed on horizontal pipelines.