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Selection and location of valves

(I) Principles for selecting valves used on water supply pipelines

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 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 areas 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) Location of valves on water supply pipelines

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, it should be set 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 residents, public toilets, etc. from the indoor water supply pipeline, and the water distribution points on the water distribution branch pipe are 3 and more than 3

7. Water outlet pipe of water pump, water suction pump of self-priming water pump

8. Water inlet and outlet pipes and drain pipe of water tank

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

10. 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, pressure relief valves and backflow preventers before and after, etc.

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

(III) Selection of Check Valve

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 when closing:

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, a check valve with a closing spring should be selected

3. When it is required to weaken the closing water hammer, a quick-closing silencer check valve or a slow-closing check valve with a damping device 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 are installed on water supply pipelines

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

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

(V) Location of the exhaust device in the water supply pipeline

1. For the water supply network used intermittently, the end and high point of the network should be equipped with an automatic exhaust valve

2. For the pipe section of the water supply network with obvious fluctuations and accumulated air, an automatic exhaust valve or manual valve has been installed at the peak point of the section for exhaust

3. For the air pressure water supply device, when using an automatic air-filling air pressure water tank, an automatic exhaust valve should be installed at the higher point of the water distribution network

Advantages and disadvantages of various valves

1. Gate valve (flange gate valve, spring-seat gate valve, stainless steel gate valve, knife gate valve, electric gate valve, pneumatic gate valve, chrome-molybdenum steel gate valve, welded gate valve, fluorine-lined gate valve, high-pressure gate valve)

The 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, fully open or fully closed. Generally, gate valves cannot be used to adjust flow. It can be used for low temperature and pressure as well as high temperature and high pressure, and can be used according to the different materials of the valve. However, gate valves are generally not used in pipelines for conveying 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 structural length is relatively short.

Disadvantages:

① The external dimensions and opening height are large, and the space required for installation 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 Long opening and closing time.

2. Butterfly valve (wafer butterfly valve, three-eccentric butterfly valve, electric butterfly valve, pneumatic butterfly valve, hard-sealed butterfly valve, flange butterfly valve, centerline butterfly valve, signal butterfly valve, handle butterfly valve, turbine butterfly valve, soft-sealed butterfly valve, fluorine-lined butterfly valve)

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, less consumables, especially used in large-caliber valves;

②Quick opening and closing, small flow resistance;

③Can 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.

3. Ball valve (electric ball valve, pneumatic ball valve, V-type ball valve, welded ball valve, three-piece ball valve, threaded ball valve, liquid ammonia ball valve, ammonia ball valve, ammonia ball valve, gas ball valve, fluorine-lined ball valve, hard-sealed ball valve, stainless steel ball valve, high-pressure ball valve, high-temperature ball valve, low-temperature ball valve)

The ball valve evolved from the plug valve. Its opening and closing part is a sphere, which is used to rotate 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 in 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 member 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 The structure is compact and light, and it can be considered as a 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 member 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 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 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 carried out around 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).

4. Stop valve (stainless steel stop valve, ammonia stop valve, ammonia stop valve, liquid ammonia stop valve, electric stop valve, high temperature stop valve, high pressure stop valve, fluorine-lined stop valve, pneumatic stop valve, low temperature stop valve)

It refers to a valve whose closing part (valve disc) moves along the center line of the valve seat. According to this movement of the valve disc, the change of the valve seat opening is proportional to the valve disc stroke. Since the valve stem opening or closing stroke of this type of valve is relatively short and has a very reliable cut-off function, and since the change of the valve seat opening is proportional to the valve disc stroke, it is very suitable for regulating flow. Therefore, this type of valve is very suitable for cutting or regulating and throttling.

Advantages:

①During the opening and closing process, the friction between the valve disc and the sealing surface of the valve body 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 There is usually only one sealing surface on the valve body and the valve disc, so the manufacturing process is relatively good and easy to maintain;

④ Because its filler is generally a mixture of asbestos and graphite, the temperature resistance level is relatively high. Generally, steam valves use stop valves.

Disadvantages:

① Since 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 (pneumatic plug valve, electric plug valve, high-temperature plug valve, fluorine-lined plug valve, rubber-lined plug valve)

The plug valve refers to a rotary valve with a plunger-shaped closing member. The channel port on the valve plug is connected or separated from the channel port on the valve body by 90° rotation to achieve opening or closing. The shape of the valve plug can be cylindrical or conical. Its 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 oil field exploitation and is also used in petrochemical industry.

6. Safety valve (full-open safety valve, spring-loaded safety valve, micro-open safety valve, liquid ammonia safety valve, gas safety valve, steam safety valve, ammonia safety valve, ammonia safety valve, low-temperature safety valve)

Safety valve refers to an overpressure protection device on a pressure container, equipment or pipeline. When the pressure in the equipment, container or pipeline exceeds the allowable value, the valve automatically opens and then discharges in full to prevent the equipment, container or pipeline and pressure from continuing to increase; when the pressure drops to the specified value, the valve should automatically close in time to protect the safe operation of the equipment, container or pipeline.

7. Steam trap (disc trap, air trap, high temperature trap, thermodynamic trap, float trap)

When the trap is used to transport steam, compressed air and other media, some condensed water will be formed. 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 use of the device. It has the following functions: ① It can quickly remove the condensed water; ② Prevent steam leakage; ③ Remove air and other non-condensable gases.

8. Pressure reducing valve (air pressure reducing valve, steam pressure reducing valve)

The pressure reducing valve is a valve that reduces the inlet pressure to a certain required outlet pressure by adjusting, and relies on the energy of the medium itself to automatically keep the outlet pressure stable.

9. Check valve (wafer check valve, liquid ammonia check valve, lift check valve, ammonia check valve, swing check valve, vertical check valve, ammonia check valve, cryogenic check valve, fluorine-lined check valve, stainless steel check valve)

Check valves are also called reverse flow valves, non-return valves, back pressure valves and one-way valves. These valves are automatically opened and closed by the force generated by the flow of the medium in the pipeline, and are a kind of automatic valve. Check valves are used in pipeline systems. Their main function is to prevent the backflow of the medium, the reversal of the pump and the drive motor, and the discharge of the container medium. Check valves can also be used in pipelines that provide supply to auxiliary systems where the pressure may rise to exceed the system pressure. They can be mainly divided into swing type (rotation according to the center of gravity) and lift type (movement along the axis).

Shanghai Ammonia Valve Manufacturer/Shanghai Yonglong Valve Factory mainly deals in: ammonia stop valves, emergency shut-off valves, electric shut-off valves, electric ball valves, pneumatic ball valves, pneumatic emergency shut-off valves, hydraulic emergency shut-off valves, gas emergency shut-off valves, liquid ammonia emergency shut-off valves, ammonia emergency shut-off valves, ammonia emergency shut-off valves, air drain valves, flame-blocking vent caps, flame arresters, current limiting valves, fuse valves, breakaway valves, electro-hydraulic valves and other mechanical supporting valves.