Valve selection of water supply and drainage pipeline and analysis of advantages and disadvantages of various valves
(1) 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, it is appropriate to use the globe valve, and when the pipe diameter is greater than 50mm, the gate valve and butterfly valve are used. 2, need to adjust the flow, water pressure when the use of regulating valve, stop valve. 3. The parts requiring small water flow resistance (such as the water pump suction pipe) should use the gate valve.
1. Selection and setting of valves:
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(1) The valves used on the water supply pipeline are generally selected according to the following principles:
1, pipe diameter is not greater than 50mm, it is appropriate to use the globe valve, pipe diameter is greater than 50mm, the use of gate valve, butterfly valve.
2, need to adjust the flow, water pressure when the use of regulating valve, stop valve.
3. The parts requiring small water flow resistance (such as the water pump suction pipe) should use the gate valve.
4. Gate valve and butterfly valve should be used on the pipe section where the water needs to flow bidirectional, and stop valve should not be used.
5. Butterfly and ball valves should be used for parts with small installation space.
6. It is appropriate to use a stop valve on the pipe section that is often opened and closed.
7. Multi-function valve should be used on the water pump outlet pipe with large caliber.
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(2) Valves shall be set in the following parts of the water supply pipeline:
1. The water supply pipeline of the residential district is from the entrance pipe section of the municipal water supply pipeline.
2. The nodes of the outdoor ring pipe network in the residential district shall be set according to the separation requirements. If the annular pipe section is too long, it is advisable to set up a segmented valve.
3. Branch pipe start or household pipe start from the water supply dry pipe in the residential district.
4. Household pipe, water meter and each branch riser (bottom of riser, upper and lower end of vertical ring pipe network riser).
5. The main pipe of the annular pipe network and the connecting pipe of the through-branch pipe network.
6. The starting point of the water distribution pipe from the indoor water supply pipe to the household and public toilet is set when there are 3 or more water distribution points on the water distribution branch pipe.
7, the water pump out of the water pipe, the suction pump of the self-filling pump.
8. Water tank inlet, outlet and discharge pipes.
9. Water filling pipe for equipment (such as heater, cooling tower, etc.).
10, sanitary appliances (such as large, urinal, wash basin, shower, etc.) water distribution pipe.
11. Some accessories, such as automatic exhaust valve, pressure relief valve, water hammer eliminator, pressure gauge, sprinkler bolt, etc., pressure reducing valve and backflow preventer before and after.
12. The lower part of the water supply network should be set up with the drain valve.
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(3) Check valves should be selected according to the installation position, the water pressure before the valve, the sealing performance requirements after closing and the size of the water hammer caused by closing and other factors:
1. Swing type, ball type and shuttle type check valves should be selected when the water pressure before the valve is small.
2. When the sealing performance is strict after closing, a check valve with a closing spring should be selected.
3. When the water hammer is required to be weakened and closed, the quick-closing silencing check valve or the slow-closing check valve with damping device should be selected.
4. The break or spool of the check valve should be able to close itself under the action of gravity or spring force.
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(4) Check valves shall be set on the following sections of the water supply pipeline:
Lead into the tube; Closed water heater or water equipment on the inlet pipe; Water pump out of the water pipe; The inlet and outlet pipes are used on the outlet pipe section of a water tank, water tower or highland pool.
Note: No check valve is required for pipe sections with pipe backflow preventers.
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(5) Exhaust devices shall be installed at the following parts of the water supply pipeline:
1. Automatic exhaust valves should be set at the end and comparative high point of the water supply network for intermittent use.
2. The pipe section of the water supply network with obvious fluctuation and accumulation of air has been equipped with automatic exhaust valve or manual valve exhaust at the peak point of the section.
3. For pneumatic water supply device, when automatic air replenishment type pneumatic water tank is used, automatic exhaust valve should be set at the comparative high point of the water distribution pipe network.
Two, the advantages and disadvantages of various valves:
1
Gate valves:
Gate valve refers to the valve whose closing parts (gate plate) move in the vertical direction along the axis of the channel. It is mainly used as a cutting medium on the pipeline, that is, it is fully opened or fully closed. Generally, gate valves cannot be used to regulate flow. It can be applied to low temperature pressure can also be applied to high temperature and high pressure, and according to the different materials of the valve. But gate valves are generally not used for conveying mud and other media in the pipeline.
Advantages: ① the fluid resistance is small; (2) Small torque required for opening and closing; (3) It can be used in the loop network where the medium flows in two directions, that is to say, the flow direction of the medium is not restricted; (4) When fully opened, the erosion of the sealing surface by the working medium is smaller than that of the stop valve; (5) The shape structure is relatively simple, and the manufacturing technology is better; ⑥ The structure length is relatively short.
Disadvantages: (1) the overall size and opening height are large, and the required installation space is also large; (2) In the process of opening and closing, the sealing surface person relative friction, friction loss is larger, even at high temperature easy to cause chafing phenomenon; (3) General gate valves have two sealing covers, which increase some difficulties for processing, grinding and maintenance; Long opening and closing time.
2
Butterfly:
The butterfly valve is a kind of valve that is used to open, close and adjust the fluid channel by rotating the disc opening and closing parts about 90°.
Advantages: (1) Simple structure, small volume, light weight, consumption, do not use in large diameter valves; (2) Fast opening and closing, small flow resistance; ③ Can be used for medium with suspended solid particles, according to the strength of the sealing surface can also be used for powder and granular medium. It can be used for bidirectional opening and closing and adjustment of ventilation and dust removal pipeline. It can be used for gas pipeline and water channel of metallurgy, light industry, electric power, petrochemical system, etc.
Disadvantages: ① The flow adjustment range is not large, when opened up to 30%, the flow will enter more than 95%. Due to the structure and sealing materials of the butterfly valve, it is not suitable for high temperature and high pressure piping system. General operating temperature below 300℃, PN40 below. ③ The sealing performance is poor compared with ball valves and globe valves, so it is used for places where the sealing requirements are not very high.
3
Ball valve:
Is evolved from the plug valve, its opening and closing part is a ball, using the ball to rotate 90 degrees around the axis of the valve stem to achieve the purpose of opening and closing. Ball valve in the pipeline is mainly used to cut off, distribute and change the direction of medium flow, designed into the V-shaped opening ball valve also has a good flow regulation function.
Advantages: (1) with relatively low flow resistance (actually 0); (2) Because it will not be stuck in the work (in the absence of lubricants), it can be reliably applied to corrosive media and low boiling point liquid; ③ In the larger pressure and temperature range, can achieve complete sealing; (4) It can realize fast opening and closing, and the opening and closing time of some structures is 0.05-0.1s, so as to ensure that it can be used in the automation system of the test bed. Quick open and close the valve, operation without impact. (5) Spherical closing parts can be automatically positioned at the boundary position; The working medium is reliable on both sides of the seal; ⑦ in fully open and fully closed, ball and seat sealing surface and medium isolation, so high speed through the valve medium will not cause sealing surface erosion; Compact structure, light weight, it can be considered to be the most reasonable valve structure for low temperature medium system; ⑨ Body symmetry, especially welded body structure, can withstand the stress from the pipe; ⑩ Closing parts can withstand the high pressure difference during closing. Completely welded valve ball valve, can be directly buried in the ground, so that the valve interior will not be corroded, relatively high service life of up to 30 years, is the ideal valve for oil and gas pipelines.
Disadvantages: (1) Because the main valve seat sealing ring material is PTFE, it is inert to almost all chemical substances, and has a small coefficient of friction, stable performance, not easy to aging, a wide range of temperature and excellent sealing performance. However, the physical properties of teflon, including high coefficient of expansion, sensitivity to cold flow, and poor thermal conductivity, require that the seat be designed around these characteristics. So, when the sealing material hardens, the reliability of the seal is compromised. Moreover, the temperature resistance of PTFE is low, and can only be used under the condition of less than 180℃. Above this temperature, the sealing material will age. In the case of long-term use, it is generally not used at 120℃. (2) Its regulating performance is worse than that of the globe valve, especially the pneumatic valve (or electric valve).
4
Globe valves:
Refers to the valve where the closing member (disc) moves along the center line of the seat. According to this form of movement of the valve disc, the change of the valve seat orifice is proportional to the valve disc stroke. Because the stem opening or closing stroke of this type of valve is relatively short, and has a very reliable cutting function, and because the change of the valve seat through the port and the stroke of the disc is directly proportional to the relationship, very suitable for flow regulation. Therefore, this type of valve is very adaptable for cutting or adjusting and throttling.
Advantages: ① In the opening and closing process, because the friction between the disc 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 1/4 of the seat channel, so it is much smaller than the gate valve; (3) Usually there is only one sealing surface on the valve body and valve disc, so the manufacturing process is better and easy to maintain. (4) Because its filler is generally a mixture of asbestos and graphite, so the temperature resistance grade is higher. General steam valves use stop valves.
Disadvantages: (1) Because the flow direction of the medium through the valve has changed, so the small flow resistance of the cut-off valve is higher than most other types of valves; ② Due to the long travel, the opening speed is slower than the ball valve.
5
Cock:
It refers to a rotary valve with the closing part as a plunger, which can be opened or closed through 90° rotation so that the port on the valve plug is communicated with or separated from the port on the valve body. The plug can be cylindrical or conical in shape. Its principle is basically similar to the ball valve, the ball valve is developed on the basis of the plug valve, it is mainly used in oil field exploitation, but also used in the petrochemical industry.
6
The relief valve:
It is used as an overpressure protection device in pressurized vessels, equipment or pipelines. When the pressure rise in the equipment, container or pipeline exceeds the allowable value, the valve will be opened automatically, and then the full discharge, to prevent the equipment, container or pipeline and pressure continue to rise; When the pressure is reduced to the specified value, the valve should be automatically closed in time, so as to protect the safe operation of equipment, containers or pipelines.
7
Steam trap:
In the transmission of steam, compressed air and other media, there will be some condensation water formation, in order to ensure the efficiency and safe operation of the device, it should be timely discharge of these useless and harmful media, to ensure the consumption and use of the device. It has the following functions: (1) can quickly eliminate the condensate produced; ② Prevent steam leakage; ③ Exclude air and other non-condensing gases.
8
Pressure reducing valve:
It is a valve that reduces the inlet pressure to a required outlet pressure by adjusting it, and relies on the energy of the medium itself to keep the outlet pressure stable automatically.
Post time: Nov-04-2022
