1、 Valve selection and setting position:

（1） The valves used in water supply pipelines are generally selected according to the following principles:
1. When the pipe diameter is not greater than 50mm, stop valves should be used, and when the pipe diameter is greater than 50mm, gate valves and butterfly valves should be used;
2. When it is necessary to adjust the flow and water pressure, regulating valves and stop valves should be used;
3. Gate valves should be used for parts requiring small water flow resistance (such as on the water pump suction pipe);
4. Gate valves and butterfly valves should be used on pipe sections where two-way flow of water is required, and stop valves should not be used;
5. Butterfly valves and ball valves should be used in places with small installation space;
6. On pipe sections that are frequently opened and closed, stop valves should be used;
7. Multifunctional valves should be used on the outlet pipes of pumps with larger diameters.
（2） The following parts of the water supply pipeline shall be equipped with valves:
1. The water supply pipeline in the residential area is led into the pipe section from the municipal water supply pipeline;
2. The nodes of the outdoor circular pipe network in residential areas should be set according to the separation requirements. When the annular pipe section is too long, segmented valves should be installed;
3. The starting end of a branch pipe or household pipe connected from the main water supply pipe of a residential area;

4. Household pipes, water meters, and branch risers (bottom of the riser, upper and lower ends of the vertical annular pipe network riser);

5. A branch pipe of a circular pipe network and a connecting pipe through a branched pipe network;
6. The starting point of the distribution pipe from the indoor water supply pipe to the household, public toilet, etc., and the water distribution branch pipe shall be set when there are three or more water distribution points;
7. An outlet pipe of a water pump and a suction pump of a self priming water pump;
8. Inlet and outlet pipes and drain pipes of the water tank;
9. Water inlet and make-up pipes for equipment (such as heaters, cooling towers, etc.);
10. Distribution pipes for sanitary appliances (such as toilets, urinals, washbasins, showers, etc.);
11. Some accessories, such as the front of automatic exhaust valve, pressure relief valve, water hammer eliminator, pressure gauge, sprinkler, pressure reducing valve, backflow preventer, etc;

12. The lowest point of the water supply network should be provided with a water release valve.

（3） Check valves should generally be selected based on factors such as their installation location, water pressure in front of the valve, sealing performance requirements after closing, and the size of water hammer caused during closing
1. When the water pressure in front of the valve is small, swing, ball, and shuttle check valves should be selected.
2. When the sealing performance after closing is required to be tight, a check valve with a closing spring should be selected.
3. When it is required to weaken the closing water hammer, it is advisable to select a quick closing silencing check valve or a slow closing check valve with a damping device.
4. The valve stem or valve core of a check valve should be able to close automatically under the action of gravity or spring force.
（4） Check valves shall be provided on the following sections of the water supply pipeline:
On the lead-in pipe; On the inlet pipe of a closed water heater or water consuming device; On the water pump outlet pipe; The water inlet and outlet pipes share the same pipe on the outlet pipe section of the water tank, water tower, and highland pool.
Note: For pipe sections equipped with pipe backflow preventers, it is not necessary to install a check valve again.
（5） The following parts of the water supply pipeline shall be equipped with exhaust devices:
1. For intermittently used water supply networks, automatic exhaust valves should be installed at the ends and highest points of the network
2. The water supply pipe network has obvious undulation and accumulation of air in the pipe section, and automatic exhaust valves or manual valves have been installed at the peak points of this section for exhaust.
3. For pneumatic water supply devices, when using automatic pneumatic water tanks, automatic exhaust valves should be installed at the highest point of the water distribution network.
2、 Advantages and disadvantages of various valves:
1. Gate valve: Gate valve refers to a valve whose closing member (gate) moves in the vertical direction of the channel axis. It is mainly used to cut off the medium on the pipeline, i.e., fully open or fully closed. Generally, gate valves cannot be used to regulate flow. It can be applied to low temperature and high pressure as well as high temperature and high pressure, and can be made of different materials according to the valve. However, gate valves are generally not used in pipelines conveying media such as mud
advantage:
① Low fluid resistance;
② The torque required for opening and closing is small;
③ It can be used in a loop network pipeline where the medium flows in two directions, which means that the flow direction of the medium is not limited;
④ When fully open, the sealing surface is less eroded by the working medium than the stop valve;
⑤ The body structure is relatively simple and the manufacturing process is good;
⑥ The structure length is relatively short.
Disadvantages:
① The overall dimension and opening height are large, and the installation space required is also large;
② During the opening and closing process, the sealing surface is subject to relative friction and large friction loss, which can easily cause scratches even at high temperatures;
③ Generally, gate valves have two sealing surfaces, which adds some difficulties to processing, grinding, and maintenance;
④ Long opening and closing time.
2. Butterfly valve: A butterfly valve is a valve that uses a disc type hoist to reciprocate by about 90 ° to open, close, and regulate fluid passages.
advantage:
① Simple structure, small size, light weight, low consumption, not suitable for use in large diameter valves;
② Quick opening and closing, small flow resistance;
③ It can be used for media with suspended solid particles, and can also be used for powdery and granular media depending on the strength of the sealing surface. It is suitable for two-way opening, closing, and adjustment of ventilation and dust removal pipelines, and is widely used in gas pipelines and waterways in metallurgical, light industry, electric power, petrochemical systems, etc.
Disadvantages:
① The flow adjustment range is not large, and when the opening reaches 30%, the flow will increase by more than 95%;
② Due to the limitations of the structure and sealing materials of butterfly valves, they are not suitable for use in high-temperature and high-pressure pipeline systems. The general working temperature is below 300 ℃ and below PN40;
③ Compared to ball valves and globe valves, the sealing performance is poor, so it is used in places where the sealing requirements are not very high.

3. Ball valve: evolved from a plug valve, its opening and closing member is a ball, which is rotated 90 ° around the axis of the valve stem to achieve the purpose of opening and closing. Ball valves are mainly used in pipelines to cut off, distribute, and change the flow direction of media. Ball valves designed with V-shaped openings also have good flow regulation functions.

advantage:
① Has the lowest flow resistance (actually 0);
② It can be reliably applied to corrosive media and low boiling point liquids because it does not get stuck during operation (when there is no lubricant);
③ Fully sealed in a wide range of pressure and temperature;
④ It can achieve rapid opening and closing, and the opening and closing time of some structures is only 0.05~0.1s to ensure that it can be used in the automation system of the test bench. When quickly opening and closing the valve, there is no impact during operation;
⑤ The spherical closure can be automatically positioned at the boundary position;
⑥ The working medium is reliably sealed on both sides;
⑦ During full opening and full closing, the sealing surfaces of the ball and valve seat are isolated from the medium, so the medium passing through the valve at high speed will not cause erosion of the sealing surface;
⑧ Due to its compact structure and light weight, it can be considered as the most reasonable valve structure for cryogenic media systems;
⑨ The valve body is symmetrical, especially the welded valve body structure, which can well withstand the stress from the pipeline;
⑩ The closing element can withstand the high pressure difference during closing The ball valve with a fully welded valve body can be directly buried underground, preventing the valve internals from being corroded, with a maximum service life of up to 30 years. It is the most ideal valve for oil and natural gas pipelines.
Disadvantages:
① "Because the main seat sealing ring material for ball valves is polytetrafluoroethylene, which is inert to almost all chemical substances, and has comprehensive characteristics such as low friction coefficient, stable performance, resistance to aging, wide range of temperature applications, and excellent sealing performance.". However, the physical characteristics 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 must revolve around these characteristics. Therefore, when the sealing material hardens, the reliability of the seal is destroyed. Moreover, the temperature resistance level of polytetrafluoroethylene is relatively low, and it can only be used at temperatures below 180 ℃. Beyond this temperature, the sealing material will age. When considering long-term use, it is generally not used at 120 ℃.
② Its regulating performance is worse than that of a shut-off valve, especially for pneumatic valves (or electric valves).
4. Stop valve: refers to a valve whose closing member (valve flap) moves along the center line of the valve seat. According to this form of movement of the valve disc, the change in the valve seat opening is in direct proportion to the valve disc stroke. Due to the relatively short opening or closing stroke of the valve stem, as well as the very reliable cutoff function, and because the change in the valve seat opening is proportional to the stroke of the valve disc, this type of valve is very suitable for regulating flow. Therefore, this type of valve is very often used for shutoff or adjustment as well as throttling.
advantage:
① During the opening and closing process, the friction force between the valve flap and the valve body sealing surface is smaller than that of the gate valve, so it is wear-resistant.
② The opening height is generally only 1/4 of the valve seat channel, so it is much smaller than the gate valve;
③ Generally, there is only one sealing surface on the valve body and valve flap, so the manufacturing process is relatively good and convenient for maintenance;
④ Due to the fact that its filler is generally a mixture of asbestos and graphite, it has a high temperature resistance rating. Generally, steam valves use globe valves.
Disadvantages:
① Due to the change in the flow direction of the medium through the valve, the minimum flow resistance of the stop valve is also higher than that of most other types of valves;
② Due to the long stroke, the opening speed is slower than the ball valve.
5. Plug valve: Refers to a rotary valve with a plunger shaped closure. Through 90 ° rotation, the passage port on the valve plug and the passage port on the valve body are connected or separated to achieve opening or closing. The shape of the valve plug can be cylindrical or conical. Its principle is basically similar to that of ball valves, which are developed on the basis of plug valves. They are mainly used for oil field exploration and also for petrochemical industry.
6. Safety valve: It refers to an overpressure protection device used on pressure vessels, equipment, or pipelines. When the pressure in the equipment, container, or pipeline increases beyond the allowable value, the valve automatically opens, and then fully discharges to prevent the equipment, container, or pipeline from continuing to increase in pressure; When the pressure drops to a specified value, the valve should automatically and timely close to protect the safe operation of equipment, containers, or pipelines.
7. Steam trap: During the transmission of steam, compressed air, and other media, some condensed water may form. In order to ensure the working efficiency and safe operation of the device, it is necessary to timely discharge these useless and harmful media to ensure the consumption and use of the device. It has the following functions: ① it can quickly remove the generated condensed water; ② Prevent steam leakage; ③ Remove air and other non condensable gases.
8. Pressure reducing valve: It is a valve that reduces the inlet pressure to a desired outlet pressure through adjustment, and relies on the energy of the medium itself to automatically maintain a stable outlet pressure.

9. Check Valve: Also known as a reverse flow valve, check valve, back pressure valve, and one-way valve. These valves are automatically opened and closed by the power generated by the flow of the medium itself in the pipeline. Check valves are used in pipeline systems to prevent media backflow, reverse rotation of pumps and drive motors, and discharge of container media. "Check valves can also be used on pipelines that provide makeup to auxiliary systems in which the pressure may rise above the system pressure. They are mainly divided into swing type (rotating according to the center of gravity) and lift type (moving along the axis).".