I. The valves used on the water supply pipeline are generally selected according to the following principles:

1. When the pipe diameter is not greater than 50mm, a stop valve should be used. When the pipe diameter is greater than 50mm, a gate valve or butterfly valve should be used. 2. When the flow rate and water pressure need to be adjusted, a regulating valve or a stop valve should be used.

3. Where the water flow resistance is small (such as on the water pump suction pipe), a gate valve should be used.

4. Gate valves and butterfly valves should be used on pipe sections where water needs to flow in both directions, and stop valves should not be used.

5. Butterfly valves and ball valves should be used in parts with small installation space.

6. Stop valves should be used on pipe sections that are frequently opened and closed.

7. Multifunctional valves should be used on the outlet pipes of water pumps with larger diameters.

II. Valves should be installed at the following locations on the water supply pipeline:

1. On the inlet pipe section of the residential area water supply pipeline from the municipal water supply pipeline.

2. At the nodes of the outdoor ring pipe network of the residential area, valves should be installed according to the separation requirements. When the ring pipe section is too long, it is advisable to install a segmented valve

3. The starting point of the branch pipe or the household pipe connected to the water supply main pipe in the residential area

4. Household pipe, water meter and each branch riser (the bottom of the riser, the upper and lower ends of the vertical ring pipe network riser)

5. The branch pipe of the ring pipe network and the connecting pipe that runs through the branch pipe network

6. The starting point of the water distribution pipe connected to the indoor water supply pipeline to the residents, public toilets, etc., when there are 3 or more water distribution points on the water distribution branch pipe

7. Water pump The outlet pipe of the self-priming water pump

8. The inlet and outlet pipes and drain pipes of the water tank

9. The water inlet and water supply pipes of the equipment (such as heaters, cooling towers, etc.)

10. The water distribution pipes of sanitary appliances (such as urinals, washbasins, showers, etc.)

11. Certain accessories, such as automatic exhaust valves, pressure relief valves, water hammer eliminators, pressure gauges, sprinkler plugs, etc., before and after the pressure reducing valve and backflow preventer, etc.

12. The drain valve should be installed at the lowest point of the water supply network

III. Check valves should generally be selected according to factors such as their installation location.

1. When the water pressure before the valve is small, swing, ball and shuttle check valves should be selected.

2. When the sealing performance after closing is strictly required, check valves with closing springs should be selected.

3. When it is required to weaken the closing water hammer, quick-closing silencer check valves or slow-closing check valves with damping devices should be selected.

4. The valve bend or valve core of the 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 the water supply pipeline:

On the inlet pipe; on the water inlet pipe of the closed water heater or water-using equipment; on the water outlet pipe of the water pump; on the outlet pipe section of the water tank, water tower, and highland pool where the inlet and outlet pipes share a pipe.

Note: The pipe section equipped with a pipeline backflow preventer does not need to be equipped with a check valve.

V. Exhaust devices should be installed at the following parts of the water supply pipeline:

1. For water supply networks used intermittently, automatic exhaust valves should be installed at the end and the highest point of the network

2. For pipe sections with obvious fluctuations and accumulated air in the water supply network, automatic exhaust valves or manual valves should be installed at the peak points of the sections for exhaust

3. For air pressure water supply devices, when using automatic air-filling air pressure water tanks, automatic exhaust valves should be installed at the highest point of the water distribution network

Advantages and disadvantages of different valves

Gate valve: Gate valve refers to a valve whose closing part (gate) moves in the vertical direction along the axis of the channel. It is mainly used to cut off the medium on the pipeline, that is, it is used fully open or fully closed. Generally, gate valves cannot be used to adjust flow. It can be used for low temperature and pressure, high temperature and high pressure, and can be used according to different valve materials. However, gate valves are generally not used in pipelines that transport media such as mud.
Advantages:

① Small fluid resistance;

② Small torque required for opening and closing;

③ Can be used on ring network pipelines where the medium flows in two directions, that is, the flow direction of the medium is not restricted;

④ When fully open, the sealing surface is less eroded by the working medium than the stop valve;

⑤ The shape and structure are relatively simple, and the manufacturing process is better;

⑥ The structure length is relatively short.

Disadvantages:

① The overall dimensions and opening height are large, and the required installation space is also large;

② During the opening and closing process, the sealing surface is relatively rubbed, the wear is large, and it is easy to cause abrasions at high temperatures;

③ Generally, gate valves have two sealing surfaces, which adds some difficulties to processing, grinding and maintenance;

④ The opening and closing time is long.

Butterfly valve: A butterfly valve is a valve that uses a disc-type opening and closing member to reciprocate about 90° to open, close and adjust the fluid channel.

Advantages:

① Simple structure, small size, light weight, and consumables. It is not used in large-diameter valves;

② Rapid opening and closing, small flow resistance;

③ It can be used for media with suspended solid particles, and can also be used for powdered and granular media according to the strength of the sealing surface. It can be used for two-way opening and closing and adjustment of ventilation and dust removal pipelines, and is widely used in gas pipelines and waterways in metallurgy, light industry, electric power, and petrochemical systems.
Disadvantages:

① The flow adjustment range is not large. When the opening reaches 30%, the flow will be more than 95%;

② Due to the limitations of the structure and sealing materials of the butterfly valve, it is not suitable for high-temperature and high-pressure pipeline systems. The general working temperature is below 300℃ and PN40;

③ The sealing performance is poorer than that of ball valves and stop valves, so it is used in places where the sealing requirements are not very high.

Ball valve: It evolved from the plug valve. Its opening and closing part is a sphere. The sphere is rotated 90° around the axis of the valve stem to achieve the purpose of opening and closing. The ball valve is mainly used to cut off, distribute and change the flow direction of the medium on the pipeline. The ball valve designed with a V-shaped opening also has a good flow regulation function.
Advantages:

① It has the lowest flow resistance (actually 0);

② Because it will not get stuck during operation (when there is no lubricant), it can be reliably used in corrosive media and low-boiling liquids;

③ It can achieve complete sealing within a large pressure and temperature range;

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 the valve is opened and closed quickly, the operation is impact-free;

⑤ The spherical closing piece can automatically position at the boundary position;

⑥ The working medium is reliably sealed on both sides;

⑦ When fully open and fully closed, the sealing surface of the ball and the valve seat is isolated from the medium, so the medium passing through the valve at high speed will not cause erosion of the sealing surface;

⑧ It has a compact structure and light weight, and it can be considered as the most reasonable valve structure for low-temperature medium 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 piece can withstand the high pressure difference when closed. ⑾ The ball valve with a fully welded valve body can be buried directly underground, so that the valve internals are not corroded, and the maximum service life can reach 30 years. It is the most ideal valve for oil and natural gas pipelines.
Disadvantages:
① Because the main valve seat sealing ring material of the ball valve is polytetrafluoroethylene, it is inert to almost all chemical substances, and has the comprehensive characteristics of low friction coefficient, stable performance, not easy to age, wide temperature application range and excellent sealing performance. However, the physical properties of polytetrafluoroethylene, including high expansion coefficient, sensitivity to cold flow and poor thermal conductivity, require that the design of the valve seat seal must be based on these characteristics. Therefore, when the sealing material hardens, the reliability of the seal is damaged. Moreover, the temperature resistance level of polytetrafluoroethylene is low and can only be used at less than 180℃. Exceeding this temperature, the sealing material will age. Considering long-term use, it is generally not used at 120℃.
② Its adjustment performance is worse than that of the stop valve, especially the pneumatic valve (or electric valve).