Selection principle and installation position of valves used in water supply pipeline
When laying the water supply pipeline, it is often necessary to install valves. There are many types of valves. In what occasions, what type of valves are selected, some of which are not fully understood, and even where the selected valves should be installed. The performance of the valves is different, and the installation location is certainly different, which will give common users headache.
The following introduces the valves in the water supply pipeline according to these situations installation position and type selection of the door shall be made into specific items:
- 1. When the pipe diameter is not more than 50 mm, stop valve should be used. When the pipe diameter is more than 50 mm, gate valve and butterfly valve should be used.
- 2. When the flow and water pressure need to be adjusted, the regulating valve and stop valve should be used.
- 3. The gate valve should be used for the parts with small flow resistance (such as water pump suction pipe).
- 4. Gate valve and butterfly valve shall be used for the pipe section with two-way flow, and stop valve shall not be used.
- 5. Butterfly valve and ball valve should be used in small installation space.
- 6. The stop valve should be used on the pipe section which is often opened and closed.
- 7. Multi function valve should be used on the outlet pipe of large diameter water pump.
Setting position of valves on water supply pipeline
- 1. The water supply pipe of residential quarter is from the leading pipe section of municipal water supply pipe
- 2. The nodes of outdoor circular pipe network in residential quarter shall be set according to the separation requirements. When the annular pipe section is too long, sectional valve should be set.
- 3. The branch pipe or household pipe from the water supply main of residential quarter.
- 4. Household pipe, water meter and branch riser (bottom of riser, upper and lower ends of vertical annular pipe network riser).
- 5. Branch pipe of ring pipe network and connecting pipe through branch pipe network.
- 6. The starting point of the water distribution pipe from the indoor water supply pipe to the household, public toilet, etc. shall be set when there are 3 or more water distribution points on the water distribution branch pipe.
- 7. The water outlet pipe of the water pump and the water suction pump of the self filling water pump.
- 8. Water inlet and outlet pipes and drain pipes of water tank.
- 9. Water supply pipe for equipment (such as heater, cooling tower, 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., pressure relief valve and backflow preventer, etc.
- 12. Drain valve should be set at the lowest part of water supply network.
Generally, the check valve shall be selected according to its installation position, water pressure in front of the valve, sealing performance requirements after closing and water hammer size caused by 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, the check valve with closing spring should be selected.
- 3. When it is required to weaken the closing water hammer, quick closing silencing check valve or slow closing check valve with damping device should be selected.
- 4. The valve break or core of check valve shall be able to close automatically under the action of gravity or spring force
- Check valve for water supply pipeline.
On the inlet pipe; on the inlet pipe of the 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 that the inlet and outlet pipes share one pipe. Note: it is not necessary to install check valve in the pipe section with pipeline backflow preventer.
Location of exhaust device in water supply pipeline
- 1. For intermittent water supply network, automatic exhaust valve shall be set at the end and the highest point of the network.
- 2. For the pipe section with obvious fluctuation and air accumulation in water supply network, automatic exhaust valve or manual valve has been set at the peak point of the section.
- 3. When the air pressure water supply device adopts the automatic air supply type air pressure water tank, the highest point of its water distribution network shall be equipped with an automatic exhaust valve.
Advantages and disadvantages of various valves
1. Gate valve
Gate valve refers to the valve that the closing part (gate) moves along the vertical direction of the channel axis. It is mainly used for cutting off medium on the pipeline, i.e. fully open or fully closed. Generally, gate valve can not be used as regulating flow. It can be applied to low temperature pressure or high temperature and pressure, and can be made of different materials according to the valve. However, the gate valve is generally not used in the pipeline conveying mud and other media:
- ① Low fluid resistance;
- ② The torque required for opening and closing is small;
- ③ Can be used in two-way flow of media on the ring network pipeline, that is to say, the flow direction of media is not limited;
- ④ When fully open, the erosion of sealing surface by working medium is smaller than that of stop valve;
- ⑤ The body structure is simple and the manufacturing process is good;
- ⑥ The structural length is relatively short.
- ① The overall dimension and opening height are large, and the installation space is also large;
- ② In the process of opening and closing, the sealing surface is relatively rubbed, and the friction loss is large, even it is easy to cause scratch at high temperature;
- ③ Generally, gate valves have two sealing surfaces, which makes it difficult to process, grind and maintain;
- ④ The opening and closing time is long.
Butterfly valve is a kind of valve which uses the disc type opening and closing parts to rotate about 90 ° to open, close and adjust the fluid channel.
- ① The utility model has the advantages of simple structure, small volume, light weight and low consumption, which can not be used in large caliber valves;
- ② Quick opening and closing, small flow resistance;
- ③ It can be used for medium with suspended solid particles, and also for powder and granular medium according to the strength of sealing surface. It can be applied to the two-way opening and closing and adjustment of the ventilation and dust removal pipeline. It is widely used in the gas pipeline and water channel of metallurgy, light industry, electric power, petrochemical system, etc.
- ① The flow regulation range is not large, when the opening reaches 30%, the flow will be more than 95%;
- ② Due to the limitation of butterfly valve structure and sealing material, it is not suitable for high temperature and high pressure pipeline system. The general working temperature is below 300 ℃ and PN40;
- ③ The sealing performance is worse than that of ball valve and globe valve, so the sealing requirements are not very high.
3. Ball valve
The ball valve is evolved from the plug valve. Its opening and closing part is a ball. The ball is rotated 90 ° around the axis of the stem to open and close. The ball valve is mainly used to cut off, distribute and change the direction of medium flow on the pipeline. The ball valve with V-shaped opening also has good flow regulation function.
- ① It has the lowest flow resistance (actually 0);
- ② It can be used in corrosive medium and low boiling point liquid reliably because it will not stick when working (when there is no lubricant);
- ③ In a large range of pressure and temperature, it can achieve complete sealing;
- ④ It can realize fast opening and closing, and the opening and closing time of some structures is only 0.05 ~ 0.1s, so as to ensure that it can be used in the automation system of the test bench. When the valve is opened and closed quickly, there is no impact during operation;
- ⑤ The spherical closure can be positioned automatically at the boundary position;
- ⑥ The working medium is sealed reliably on both sides;
- ⑦ When the valve is fully open and 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 the erosion of the sealing surface;
- ⑧ Because of its compact structure and light weight, it can be considered as the most reasonable valve structure for low temperature medium system;
- ⑨ The valve body is symmetrical, especially the welded valve body structure, which can well bear the stress from the pipeline;
- ⑩ The closing piece can withstand the high pressure difference during closing.
- ⑪ The ball valve with fully welded valve body can be directly buried in the ground, so that the internal parts of the valve are not eroded, and the maximum service life can reach 30 years. It is the most ideal valve for oil and gas pipelines.
- ① Because the most important sealing ring material of the valve seat is polytetrafluoroethylene, it is inert to almost all chemical substances, and has the comprehensive characteristics of small friction coefficient, stable performance, not easy to aging, wide range of temperature application and excellent sealing performance. But the physical characteristics of PTFE, including high expansion coefficient, sensitivity to cold flow and poor thermal conductivity, require that the design of valve seat seal must be based on these characteristics. Therefore, when the sealing material becomes hard, the reliability of the seal will be damaged. Moreover, the temperature resistance grade of polytetrafluoroethylene is low, and it can only be used under the condition of less than 180 ℃. Beyond this temperature, the sealing material will age. In consideration of long-term use, it is generally not used at 120 ℃.
- ② Its regulating performance is worse than that of stop valve, especially pneumatic valve (or electric valve).
4. Stop valve
It refers to the valve where the closing piece (disc) moves along the center line of the valve seat. According to this movement of the disc, the change of the valve seat port is in direct proportion to the disc stroke. Because of the relatively short opening or closing stroke of the valve stem, and the very reliable cut-off function, and because the change of the valve seat port is proportional to the stroke of the valve disc, it is very suitable for the flow regulation. Therefore, this type of valve can be used for shut-off or regulation and throttling.
- ① In the process of opening and closing, 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.
- ② Generally, the opening height is 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 disc, so the manufacturing process is relatively good and easy to maintain;
- ④ As the filler is generally a mixture of asbestos and graphite, the temperature resistance grade is higher. Generally, stop valves are used for steam valves.
- ① Because 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;
- ② Due to the long stroke, the opening speed is slower than the ball valve.
5. Plug valve
It refers to a kind of rotary valve with a plunger shaped closure member, through 90 ° rotation, the passage port on the valve plug is connected or separated from the passage port on the valve body, so as to open or close the valve. The shape of the plug can be cylindrical or conical. The principle of the ball valve is similar to that of the ball valve. The ball valve is developed on the basis of the plug valve. It is mainly used in oil field exploitation and petrochemical industry.
6. Safety valve
It refers to the overpressure protection device on the pressure vessel, equipment or pipeline. When the pressure rise in the equipment, container or pipeline exceeds the allowable value, the valve will open automatically, and then discharge in full amount to prevent the equipment, container or pipeline and pressure from rising continuously; when the pressure drops to the specified value, the valve shall close automatically and timely to protect the safe operation of the equipment, container or pipeline.
7. Steam trap
There will be some condensed water 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 medium should be discharged in time to ensure the consumption and use of the device. It has the following functions:
- ① It can quickly remove the condensate produced;
- 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 certain required outlet pressure through regulation, and makes the outlet pressure automatically keep stable depending on the energy of the medium itself.
9. Check valve
Also known as counter flow valve, check valve, back pressure valve and check valve. These valves are automatically opened and closed by the force generated by the flow of the pipeline medium itself, belonging to an automatic valve. Check valve is used in pipeline system, its main function is to prevent medium backflow, pump and drive motor reverse rotation, as well as container medium discharge. The check valve can also be used to supply the auxiliary system whose pressure may rise above the system pressure. It can be divided into swing type (rotating according to the center of gravity) and lift type (moving along the axis).
Source: China Valve Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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