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Valve selection and setting: (I) Valves used in water supply pipelines are generally selected according to the following principles: 1. When the pipe diameter is not greater than 50 mm, globe valves are preferred; for diameters larger than 50 mm, gate valves or butterfly valves are used. 2. Control valves or globe valves are suitable when it is necessary to regulate flow rate or water pressure. 3. Gate valves are appropriate in areas where low water flow resistance is required (such as on the suction pipes of water pumps). 4. Gate valves or butterfly valves should be used in sections where water flow needs to occur in both directions; globe valves should not be used in such cases. 5. Butterfly valves and ball valves are suitable for areas with limited installation space. 6. Globe valves are preferable in sections that are frequently opened and closed. 7. Multi-functional valves are suitable for the outlet pipes of water pumps with large diameters. (II) Valves should be installed at the following locations in water supply pipelines: 1. At the connection point between the municipal water supply pipeline and the water supply pipelines in residential areas. 2. At the nodes of the outdoor ring network in residential areas, valves should be installed as required for separation purposes. When the length of the circular pipe section is too great, segmental valves should be installed. 3. At the starting point of the branch pipes extending from the main water supply pipe in residential areas, or at the starting point of the pipes leading to individual households. 4. At the pipes leading to households, water meters, and various branch risers (at the bottom of the risers, as well as at the upper and lower ends of vertical circular pipe networks). 5. At the branch pipes of circular pipe networks and the connecting pipes that link together branched pipe networks. 6. At the starting point of the distribution pipes that carry indoor water supply to households, public restrooms, etc.; such valves should be installed when there are 3 or more water distribution points on the branch pipes. 7. At the outlet pipe of water pumps, and at the suction pump of self-priming water pumps. 8. At the inlet, outlet, and drain pipes of water tanks. 9. At the water supply pipes for equipment such as heaters and cooling towers. 10. At the water distribution pipes for sanitary fixtures such as toilets, washbasins, and showers. 11. At certain accessories such as automatic air release valves, pressure relief valves, water hammer arrestors, pressure gauges, faucets, etc., as well as before and after pressure reducing valves and check valves. 12. A drain valve should be installed at the lowest point of the water supply network. (III) Check valves should generally be selected based on factors such as their installation location, the water pressure before the valve, the requirements for sealing performance after closure, and the magnitude of water hammer generated when the valve is closed. 1. When the water pressure before the valve is low, swing check valves, ball check valves, and plug check valves are suitable choices. 2. When strict sealing performance after closure is required, check valves equipped with closing springs are appropriate. 3. To reduce water hammer during closure, rapid-closing noise-reducing check valves or check valves with damping devices are advisable. 4. The valve disc or core of a check valve should be able to close automatically under the action of gravity or spring force. (IV) Check valves should be installed on the following sections of water supply pipes: on the inlet pipes ； On the inlet pipe of a sealed water heater or water-using device ； On the water pump outlet pipe ； On the outlet pipe section of water tanks, water towers, and elevated water reservoirs that use a single pipe for both inlet and outlet water. Note: Pipe sections equipped with pipe check valves do not require a check valve to be installed. (5) Exhaust devices shall be installed at the following locations of the water supply pipes: 1. In water supply networks that are used intermittently, automatic exhaust valves shall be installed at the end of the network and at its highest point ； 2. In sections of the water supply network where air accumulates due to significant fluctuations, automatic exhaust valves or manual valves have been installed at the peaks of these sections to release the air ； 3. For pressure water supply systems, when an automatic air-supplementing pressure tank is used, an automatic exhaust valve should be installed at the highest point of the water distribution network. Advantages and disadvantages of various valves: 1. Gate valve: A gate valve is a type of valve in which the closing element (gate) moves vertically along the axis of the passage; it is primarily used in pipelines to shut off the flow of medium, that is, to either fully open or fully close it. Generally, gate valves cannot be used to regulate flow. It can be used in low-temperature and low-pressure conditions as well as in high-temperature and high-pressure conditions, and it can be adapted to different valve materials. However, gate valves are generally not used in pipelines transporting media such as slurry. Advantages: ① Low fluid resistance ； ②The torque required to open and close is low ； ③It can be used in ring piping systems where the medium flows in both directions; in other words, the flow direction of the medium is not restricted ； ④When fully open, the sealing surface is subjected to less erosion by the working medium compared to a globe valve ； ⑤Its structural design is relatively simple, and it is easy to manufacture ； ⑥The structural length is relatively short. Disadvantages: ① It has large external dimensions and opening height, requiring a lot of space for installation ； ②During the opening and closing process, relative friction occurs between the sealing surfaces, resulting in significant wear; in addition, high temperatures can easily lead to scuffing ； ③Generally, gate valves have two sealing surfaces, which adds some difficulty to machining, grinding, and maintenance ； ④ The opening and closing time is long. 2. Butterfly valve: A butterfly valve is a type of valve that uses a disc-shaped element that rotates back and forth by about 90° to open, close, and regulate the flow of fluid. Advantages: ① Simple structure, small size, light weight, low material consumption; not suitable for large-diameter valves ； ②Fast opening and closing, low flow resistance ； ③It can be used in media containing suspended solid particles, and depending on the strength of the sealing surface, it can also be used for powdered and granular media. It can be used for two-way opening, closing, and adjustment in ventilation and dust removal pipelines, and is widely applied to gas pipes and water pipelines in metallurgy, light industry, power, and petrochemical systems. Disadvantages: ① The flow regulation range is limited; when it is set to 30%, the flow rate exceeds 95% ； ②Due to the structure of butterfly valves and the limitations of their sealing materials, they are not suitable for use in high-temperature and high-pressure pipeline systems. The normal operating temperature is below 300°C, and the pressure rating is below PN40 ； ③Its sealing performance is inferior to that of ball valves and globe valves, so it is used in applications where high sealing requirements are not necessary. 3. Ball valve: Derived from plug valves, its closing element is a sphere. The sphere rotates 90° around the axis of the valve stem to achieve the purpose of opening and closing. Ball valves are primarily used on pipelines to shut off, distribute, and change the direction of fluid flow; those designed with a V-shaped opening also possess excellent flow regulation capabilities. Advantages: ① It has the lowest flow resistance (actually 0) ； ②It does not get stuck during operation (without lubricant), allowing it to be reliably used in corrosive media and low-boiling-point liquids ； ③Complete sealing can be achieved within a wide range of pressures and temperatures ； ④Fast opening and closing can be achieved; the opening and closing time for certain structures is as low as 0.05–0.1 seconds, ensuring their suitability for use in automated systems on test benches. When the valve is opened and closed quickly, the operation is shock-free ； ⑤The spherical closure element can automatically position itself at the boundary position ； ⑥The working medium is reliably sealed on both sides ； ⑦When in the fully open and fully closed positions, the sealing surfaces of the ball and the valve seat are separated from the medium, so the medium flowing through the valve at high speed does not cause erosion of these sealing surfaces ； ⑧With its compact design and low weight, it can be considered the most suitable valve structure for low-temperature medium systems ； ⑨The valve body is symmetrical; especially in the case of welded valve bodies, it can withstand stresses from the pipelines effectively ； ⑩The closing element can withstand the high pressure difference during closure. ⑾Ball valves with fully welded valve bodies can be buried directly underground, preventing the internal components of the valve from being corroded; their maximum service life can reach 30 years, making them the ideal valves for oil and gas pipelines. Disadvantages: ① Since the main material used for the seat seal ring in ball valves is polytetrafluoroethylene, it is inert to almost all chemicals. It also boasts a low friction coefficient, stable performance, resistance to aging, a wide temperature range of operation, and excellent sealing properties. However, the physical properties of polytetrafluoroethylene, including its high coefficient of expansion, sensitivity to cold flow, and poor thermal conductivity, require that the design of the valve seat seal take these properties into account. Therefore, when the sealing material hardens, the reliability of the seal is compromised. Moreover, polytetrafluoroethylene has a low temperature resistance and can only be used at temperatures below 180°C. Above this temperature, the sealing material will age. When considering long-term use, it is generally not used at 120°C. ②Its regulating performance is somewhat inferior to that of globe valves, especially pneumatic valves (or electric valves). 4. Globe valve: It refers to a valve in which the closing element (valve disc) moves along the center line of the valve seat. Based on this manner of movement of the valve disc, the change in the valve seat opening is directly proportional to the stroke of the valve disc. Due to the relatively short opening and closing stroke of the valve stem in this type of valve, as well as its highly reliable shut-off function, and because the change in the valve seat orifice is proportional to the stroke of the valve disc, it is very suitable for regulating flow rate. Therefore, this type of valve is very suitable for use in cutting off or regulating flow, as well as for throttling. Advantages: ① During opening and closing, the frictional force between the valve disc and the sealing surface of the valve body is lower than that of gate valves, thus offering better wear resistance ； ②The opening height is generally only 1/4 of the valve seat passage, so it is much smaller than gate valves ； ③Usually, there is only one sealing surface on the valve body and the valve disc, which makes the manufacturing process simpler and facilitates maintenance ； ④Since its filler is generally a mixture of asbestos and graphite, it has a high temperature resistance rating. Gauge valves are generally used for steam valves. Disadvantages: ① Since the flow direction of the medium through the valve changes, the minimum flow resistance of a globe valve is also higher than that of most other types of valves ； ②Due to the long travel distance, its opening speed is slower than that of a ball valve. 5. Plug valve: It is a rotary valve whose closing element is in the form of a plunger; by rotating it 90°, the passage on the plunger is connected to or separated from the passage on the valve body, thereby enabling the valve to be opened or closed. The shape of the valve plug can be cylindrical or conical. Its principle is basically similar to that of a ball valve, which was developed from a plug valve. It is primarily used in oil field extraction, as well as in the petrochemical industry. 6. Safety valve: It refers to a device used as an overpressure protection mechanism in pressurized vessels, equipment, or pipelines. When the pressure inside a device, container, or pipeline exceeds the permissible limit, the valve automatically opens to allow full discharge, thereby preventing any further increase in pressure within the device, container, or pipeline ； When the pressure drops to the specified value, the valve should close automatically and promptly, thereby ensuring the safe operation of the equipment, containers, or pipelines. 7. Steam traps: When conveying media such as steam and compressed air, some condensate water is formed. To ensure the efficiency and safe operation of the equipment, it is necessary to discharge this unnecessary and harmful fluid promptly, so as to maintain proper functioning of the equipment. It has the following functions: ① It can quickly remove the condensed water that is generated ； ②Prevent steam leakage ； ③Remove air and other non-condensable gases. 8. Pressure relief valve: It is a valve that reduces the inlet pressure to a desired outlet pressure through regulation, and relies on the energy of the medium itself to maintain the outlet pressure stable automatically. 9. Check valve: Also known as a backflow valve, non-return valve, backpressure valve, and one-way valve. These valves open and close automatically due to the force generated by the flow of the medium itself within the pipeline; they are a type of automatic valve. Check valves are used in piping systems; their main functions are to prevent backflow of the medium, to stop the pump and driving motor from rotating in reverse, and to allow the release of medium from containers. Check valves can also be used in pipelines that supply auxiliary systems whose pressure may rise above the system pressure; they can mainly be divided into swing type (rotating around its center of gravity) and lift type (moving along its axis).