1. Valve selection and setting location:
(1) Valves used on water supply pipelines are generally selected according to the following principles:
1. When the pipe diameter is not more than 50mm, a stop valve should be used; when the pipe diameter is more than 50mm, a gate valve or butterfly valve should be used
2, when the flow and water pressure need to be adjusted, a regulating valve and a stop valve should be used
3. For parts that require low flow resistance (such as on the suction pipe of a pump), gate valves should be used
4. Gate valves and butterfly valves should be used on pipe sections where water flow needs to flow in both directions, and stop valves should not be used
5. Butterfly valves and ball valves should be used in places where the installation space is small
6. It is advisable to use shut-off valves on pipe sections that are frequently opened and closed
7, a multi-function valve should be used on the outlet pipe of the pump with a larger diameter
(2) Valves should be installed at the following locations on the water supply pipeline:
1. The water supply pipeline of the residential quarter is from the introduction pipe section of the municipal water supply pipeline
2. The nodes of the outdoor loop pipe network of the residential quarter should be set up according to the separation requirements. When the annular pipe section is too long, a segmented valve should be installed
3. The beginning of the branch pipe connected to the main water supply pipe of the residential area or the beginning of the household pipe
4. Household pipes, water meters and branch risers (the bottom of the riser, the upper and lower ends of the riser of the vertical ring pipe network)
5. The branch pipes of the ring-shaped pipe network and the connecting pipes through the branched pipe network
6. The end of the water distribution pipe connecting the indoor water supply pipe to the households, public toilets, etc., and the water distribution point on the water distribution branch pipe is set when there are 3 or more
7. Outlet pipe of water pump, suction pump of self-filling water pump
8. The inlet and outlet pipes and drain pipes of the water tank
9. The water inlet and make-up pipes of equipment (such as heaters, cooling towers, etc.)
10. Water distribution pipes for sanitary appliances (such as urinals, washbasins, showers, etc.)
11. Some accessories, such as automatic exhaust valve, pressure relief valve, water hammer eliminator, pressure gauge, sprinkler, etc., before and after pressure reducing valve and backflow preventer, etc.
12. A drain valve should be installed at the lowest point of the water supply network
Advantages and disadvantages of valves
(3) Check valves should generally be selected according to factors such as their installation location, water pressure before the valve, sealing performance requirements after closing, and the size of the water hammer caused by closing
1. If the water pressure in front of the valve is small, it is advisable to use swing, ball and shuttle check valves
2. When the airtight performance after closing is tight, a check valve with closing spring should be selected
3. When it is required to weaken the shut-off water hammer, a quick-closing muffler check valve or a slow-closing check valve with a damping device should be selected
4. The valve break or spool of the 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 pipe sections of the water supply pipeline:
on the introduction pipe; on the inlet pipe of a closed water heater or water equipment; on the 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 are combined.
Note: The pipe section equipped with the pipe backflow preventer does not need to install a check valve.
(5) Exhaust devices should be installed in the following parts of the water supply pipeline:
1. For the water supply pipe network used intermittently, the end and highest point of the pipe network should be equipped with automatic exhaust valves
2. There are obviously undulating pipe sections in the water supply network that accumulate air, and automatic exhaust valves or manual valves have been set up at the peak of this section.
3. Air pressure water supply device. When automatic air-supply air pressure water tank is used, the highest point of the water distribution pipe network should be equipped with an automatic exhaust valve
2. Advantages and disadvantages of various valves:
1. Shanghai Chuanhu Gate Valve: Gate valve refers to a valve whose closing member (gate) moves along the vertical direction of the channel axis. It is mainly used as a cut-off medium in the pipeline, that is, fully open or fully closed. Generally, the gate valve cannot be used as an adjustment flow. It can be applied to low temperature and pressure as well as high temperature and high pressure, and can be based on different materials of the valve. But gate valves are generally not used in pipelines that transport mud and other media
advantages:
①The fluid resistance is small;
②The torque required for opening and closing is small;
③It can be used on the ring network pipeline where the medium flows in both directions, that is to say, the flow direction of the medium is not restricted;
④When fully open, the erosion of the sealing surface by the working medium is smaller than that of the stop valve;
⑤The body structure is relatively simple, and the manufacturing process is better;
⑥The structure length is relatively short.
Disadvantages:
①The overall dimensions and opening height are large, and the installation space required is also large;
②In the process of opening and closing, the sealing surface is relatively rubbed by people, and the abrasion is large, even at high temperature, it is easy to cause abrasion;
③Generally, gate valves have two sealing surfaces, which adds some difficulties to processing, grinding and maintenance;
④Long opening and closing time.
2. 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:
①Simple structure, small size, light weight, saving consumables, do not use in large-diameter valves;
②Rapid opening and closing, low flow resistance;
③It can be used for media with suspended solid particles, and it can also be used for powder and granular media depending on the strength of the sealing surface. It can be applied to the 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:
①The flow adjustment range is not large, when the opening reaches 30%, the flow will enter more than 95%;
②Due to the limitation of the structure of the butterfly valve and the sealing material, it is not suitable for use in high temperature and high pressure piping systems. The general working temperature is below 300℃ and below PN40;
③The sealing performance is worse than that of ball valves and globe valves, 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 part is a sphere, which uses the sphere to rotate 90° around the axis of the valve stem to achieve the purpose of opening and closing. The ball valve is mainly used for cutting off, distributing and changing the flow direction of the medium in the pipeline. The ball valve designed as a V-shaped opening also has a good flow adjustment function.
advantages:
①has the lowest flow resistance (actually 0);
②Because it will not get stuck when working (when there is no lubricant), it can be reliably used in corrosive media and low-boiling liquids;
③In a larger pressure and temperature range, it can achieve complete sealing;
④It can realize fast 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 opening and closing the valve quickly, the operation has no impact;
⑤The spherical closing piece can be automatically positioned on the boundary position;
⑥The working medium is reliably sealed on both sides;
⑦When fully open and fully closed, the sealing surface of the ball and valve seat is isolated from the medium, so the medium passing through the valve at high speed will not cause the erosion of the sealing surface;
⑧ compact structure and light weight, it can be considered as the most reasonable valve structure for cryogenic medium system;
⑨The valve body is symmetrical, especially the welded valve body structure, which can withstand the stress from the pipeline well;
⑩The closing piece can withstand the high pressure difference when closing. ⑾The ball valve with fully welded body can be directly buried in the ground, so that the internal parts of the valve are not corroded, and the maximum service life can reach 30 years. It is the most ideal valve for oil and natural gas pipelines. It is a professional manufacturer of Shanghai Chuanhu Valve Ball Valve.
Disadvantages:
①Because the main seat sealing ring material of the ball valve is polytetrafluoroethylene, it is inert to almost all chemical substances, and has a small friction coefficient, stable performance, not easy to age, wide temperature application range and excellent sealing performance The comprehensive characteristics. However, the physical properties of PTFE, including high expansion coefficient, sensitivity to cold flow and poor thermal conductivity, require the design of valve seat seals to focus on these characteristics. Therefore, when the sealing material becomes hard, the reliability of the seal is impaired. Moreover, PTFE has a low temperature resistance grade and can only be used at less than 180°C. Above this temperature, the sealing material will deteriorate. In the case of long-term use, it will generally only be used at 120°C.
②Its regulation performance is worse than that of globe valves, especially pneumatic valves (or electric valves).
Advantages and disadvantages of valves
4. Cut-off valve: refers to a valve whose closing part (disc) moves along the center line of the valve seat. According to this movement of the valve disc, the change of the valve seat port is proportional to the valve disc stroke. Since the opening or closing stroke of the valve stem of this type of valve is relatively short, and it has a very reliable cut-off function, and because the change of the valve seat port is in direct proportion to the stroke of the valve disc, it is very suitable for flow adjustment. Therefore, this type of valve is very suitable for cutting off or regulating and throttling.
advantages:
①During the opening and closing process, the friction between the disc and the sealing surface of the valve body is smaller than that of the gate valve, so it is wear-resistant.
②The opening height is generally only 1/4 of the valve seat passage, so it is much smaller than the gate valve;
③Usually there is only one sealing surface on the valve body and the disc, so the manufacturing process is relatively good and easy to maintain;
④Because the filler is generally a mixture of asbestos and graphite, the temperature resistance level is higher. Generally steam valves use stop valves.
Disadvantages:
①As the flow direction of the medium through the valve has changed, the minimum flow resistance of the stop valve is also higher than that of most other types of valves;
②Due to the longer stroke, the opening speed is slower than that of the ball valve.
5. Plug valve: refers to a rotary valve with a plunger-shaped closing part. The passage port on the valve plug is communicated with or separated from the passage port on the valve body through a 90° rotation to realize opening or closing. The shape of the valve plug can be cylindrical or conical. The principle is basically similar to that of the ball valve. The ball valve is developed on the basis of the plug valve. It is mainly used for oilfield exploitation, but also for petrochemical industry.
6. Safety valve: refers to the pressure vessel, equipment or pipeline, as an overpressure protection device. When the pressure in the equipment, container or pipeline rises above the allowable value, the valve automatically opens, and then the full amount is discharged to prevent the equipment, container or pipeline and the pressure from continuing to rise; when the pressure drops to the specified value, the valve should automatically Close in time to protect the safe operation of equipment, containers or pipelines.
7. Steam trap: Some condensed water will be formed in the medium of conveying steam, compressed air, etc. In order to ensure the working efficiency and safe operation of the device, these useless and harmful media should be discharged in time to ensure the consumption and consumption of the device. use. It has the following functions: ①It can quickly remove the condensed water produced; ②Prevent steam leakage; ③Exclude air and other non-condensable gases.
8. Pressure reducing valve: It is a valve that reduces the inlet pressure to a certain required 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 reverse valve, check valve, back pressure valve and one-way valve. These valves are automatically opened and closed by the force generated by the flow of the medium in the pipeline, and belong to an automatic valve. The check valve is used in the pipeline system, and its main function is to prevent the medium from flowing back, preventing the pump and the drive motor from reversing, and releasing the container medium. Check valves can also be used to supply pipelines for auxiliary systems whose pressure may rise above the system pressure. They can be divided into swing type (rotating by the center of gravity) and lifting type (moving along the axis).
