A compilation of the advantages and disadvantages of various valves!

I. Valve Selection and Installation Location:

(I) Valves used on water supply pipelines should generally be selected according to the following principles:

1. For pipe diameters not exceeding 50mm, gate valves are recommended; for pipe diameters exceeding 50mm, gate valves or butterfly valves are recommended.

2. Regulating valves or gate valves are recommended when flow rate and water pressure need to be adjusted.

3. Gate valves are recommended for locations requiring low flow resistance (such as on water pump suction pipes).

4. Gate valves or butterfly valves should be used on pipe sections where bidirectional water flow is required; gate valves should not be used.

5. Butterfly valves or ball valves are recommended for locations with limited installation space.

6. Gate valves are recommended for pipe sections that are frequently opened and closed.

7. Multifunctional valves are recommended for water pump outlet pipes with larger diameters.

(II) Valves should be installed at the following locations on water supply pipelines:

1. The inlet pipe section of the water supply pipeline in residential areas from the municipal water supply pipeline.

2. At the nodes of the outdoor ring network in residential areas, valves should be installed according to the separation requirements. When the ring pipe section is too long, segmented valves should be installed.

3. The beginning of the branch pipe or the beginning of the household connection pipe from the main water supply pipe of the residential area.

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

5. Branch pipes of the ring network and connecting pipes connecting to the branch network.

6. The beginning of the water distribution pipe from the indoor water supply pipe to residents, public toilets, etc., with water distribution points on the branch pipes at point 3. For units of 1 or more:

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

8. Water tank inlet, outlet, and drain pipes

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

10. Water distribution pipes for sanitary ware (such as urinals, washbasins, showers, etc.)

11. Certain accessories, such as automatic air vents, pressure relief valves, water hammer eliminators, pressure gauges, sprinkler heads, etc., and their pre- and post-pressurization valves. Before and after the flow preventer, etc.

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

(III) Check valves should generally be selected based on factors such as their installation location, upstream water pressure, required sealing performance after closure, and the magnitude of water hammer caused during closure.

1. When the upstream water pressure is low, swing, ball, and shuttle check valves are recommended.

2. When a tight sealing performance is required after closure, a check valve with a closing spring is recommended.

3. When it is required to reduce water hammer during closure, a quick-closing silent check valve or a slow-closing check valve with a damping device is recommended.

4. The valve flap or valve core of the check valve should be able to close automatically under 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 inlet pipe of a closed water heater or water-using equipment; on the outlet pipe of a water pump; on the outlet pipe section of a water tank, water tower, or elevated water pool where the inlet and outlet pipes share a single pipeline. Note: Pipe sections equipped with backflow preventers do not require check valves.

(V) Air venting devices should be installed at the following locations in water supply pipelines:

1. For intermittently used water supply networks, automatic air vents should be installed at the ends and highest points of the network.

2. For water supply network sections with significant undulations and air accumulation, automatic or manual air vents should be installed at the peak points of those sections.

3. For pneumatic water supply systems, when using automatic air-replenishing pneumatic water tanks, automatic air vents should be installed at the highest points of the distribution network.

II. Advantages and disadvantages of various valves:

1. Gate valve: A gate valve is a valve in which the closing element (gate) moves vertically along the channel axis. It is mainly used to cut off the medium in pipelines, i.e., fully open or fully closed. Generally, gate valves cannot be used to regulate flow. It can be used at low temperatures and high pressures, and its application can vary depending on the valve material. Gate valves are generally not used in pipelines transporting media such as slurry.

Advantages:

① Low fluid resistance;

② Lower torque required for opening and closing;

③ Can be used in ring network pipelines where the medium flows in both directions, meaning the flow direction is unrestricted;

④ Less erosion of the sealing surface by the working medium when fully open compared to a globe valve;

⑤ Simpler structure and easier manufacturing;

⑥ Shorter structural length.

Disadvantages:

① Larger overall dimensions and opening height, requiring more installation space;

② Higher friction between the sealing surfaces during opening and closing, leading to greater wear and even scratches at high temperatures;

③ Gate valves generally have two sealing surfaces, increasing the difficulty of machining, grinding, and maintenance;

④ Longer opening and closing time.

2. Butterfly Valve: A butterfly valve is a type of valve that uses a disc-shaped opening and closing element that rotates approximately 90° to open, close, and regulate the fluid passage. Advantages:

① Simple structure, small size, light weight, and low material consumption, especially suitable for large-diameter valves;

② Quick opening and closing, low flow resistance;

③ Can be used for media containing suspended solid particles, and depending on the strength of the sealing surface, it can also be used for powdery and granular media. It is suitable for bidirectional opening, closing, and regulation in ventilation and dust removal pipelines, and is widely used in gas pipelines and waterways in metallurgical, light industrial, power, and petrochemical systems.

Disadvantages:

① The flow regulation range is not large; when the opening reaches 30%, the flow rate will exceed 95%;

② Due to the limitations of the butterfly valve's structure and sealing materials, it is not suitable for high-temperature and high-pressure pipeline systems. The general operating temperature is below 300℃, and the PN40 level is below 40;

③ The sealing performance is relatively poor compared to ball valves and gate valves, so it is used in applications where sealing requirements are not very high.

3. Ball Valve: Evolved from the plug valve, its opening and closing element is a ball, which rotates 90° around the valve stem axis to achieve opening and closing. Ball valves are mainly used in pipelines to cut off, distribute, and change the flow direction of media. Ball valves designed with a V-shaped opening also have good flow regulation capabilities.

Advantages:

① Lowest flow resistance (virtually zero);

② Reliable application in corrosive media and low-boiling-point liquids because they do not jam during operation (without lubricant);

③ Achieves complete sealing over a wide pressure and temperature range;

④ Enables rapid opening and closing; some designs have opening and closing times of only 0.05~0.1s, ensuring compatibility with automated testing systems. ⑤ The ball valve operates without impact during rapid opening and closing;

⑥ The ball-shaped closing element automatically positions itself at the boundary;

⑦ The working medium is reliably sealed on both sides;

⑦ When fully open and fully closed, the sealing surfaces of the ball and seat are isolated from the medium, thus preventing erosion of the sealing surfaces by high-speed medium passing through the valve;

⑧ The compact structure and light weight make it arguably the most suitable valve structure for cryogenic media systems;

⑨ The symmetrical valve body, especially the welded valve body structure, can effectively withstand stress from the pipeline;

⑩ The closing element can withstand the high pressure differential during closure;

⑪ Ball valves with fully welded bodies can be directly buried underground, protecting the valve internals from corrosion, and have a maximum service life of up to 30 years, making them ideal valves for oil and gas pipelines.

Disadvantages:

① Because the main material of the ball valve's seat sealing ring is polytetrafluoroethylene (PTFE), it is inert to almost all chemical substances and possesses comprehensive characteristics such as low coefficient of friction, stable performance, resistance to aging, wide temperature range, and excellent sealing performance. However, the physical properties of PTFE, including its high coefficient of expansion, sensitivity to cold flow, and poor thermal conductivity, necessitate that the valve seat seal design be tailored to these characteristics. Therefore, when the sealing material hardens, the reliability of the seal is compromised. Furthermore, PTFE has a low temperature resistance rating, allowing use only below 180°C. Above this temperature, the sealing material will age. Considering long-term use, it is generally only avoided at 120°C.

② Its regulating performance is somewhat inferior to that of a gate valve, especially pneumatic (or electric) valves.

4. Gate valve: This refers to a valve where the closing element (valve disc) moves along the centerline of the valve seat. Based on this movement of the valve disc, the change in the valve seat opening is directly proportional to the valve disc stroke. Because this type of valve has a relatively short opening or closing stroke and a very reliable shut-off function, and because the change in the valve seat opening is directly proportional to the valve disc stroke, it is very suitable for flow regulation. Therefore, this type of valve is very suitable for shut-off, regulation, and throttling purposes. Advantages:

① During opening and closing, the friction between the valve disc and the valve body sealing surface is less than that of a gate valve, resulting in better wear resistance.

② The opening height is generally only 1/4 of the valve seat passage, much smaller than that of a gate valve.

③ There is usually only one sealing surface on the valve body and valve disc, making it easier to manufacture and maintain.

④ Because its packing is generally a mixture of asbestos and graphite, it has a higher temperature resistance rating. Gate valves are commonly used for steam valves.

Disadvantages:

① Because the flow direction of the medium changes through the valve, the minimum flow resistance of a gate valve is higher than that of most other types of valves.

② Due to its longer stroke, the opening speed is slower than that of a ball valve.

5. Plug Valve: This is a rotary valve with a plunger-shaped closing element. A 90° rotation opens or closes the valve by connecting or separating the passage on the plug with the passage on the valve body. The plug can be cylindrical or conical. Its principle is basically similar to that of a ball valve. Ball valves were developed based on plug valves and are mainly used in oilfield extraction, but also in petrochemicals.

6. Safety Valve: This is a device used as overpressure protection in pressurized containers, equipment, or pipelines. When the pressure inside the equipment, container, or pipeline rises above the allowable value, the valve automatically opens and then fully discharges the pressure to prevent further increases. When the pressure drops to the specified value, the valve should automatically and promptly close, thus protecting the safe operation of the equipment, container, or pipeline.

7. Steam Trap: In the process of conveying media such as steam and compressed air, some condensate will form. To ensure the efficiency and safe operation of the equipment, this useless and harmful medium should be discharged in a timely manner to ensure the consumption and use of the equipment. It has the following functions: ① Quickly removes the generated condensate; ② Prevents steam leakage; ③ Removes air and other non-condensable gases.

8. Pressure Reducing Valve: This is a valve that reduces the inlet pressure to a desired outlet pressure through adjustment and automatically maintains a stable outlet pressure by relying on the energy of the medium itself.

9. Check valve: Also known as a backflow valve, non-return valve, back pressure valve, and one-way valve. These valves open and close automatically based on the force generated by the flow of the medium in the pipeline, and are a type of automatic valve. Check valves are used in pipeline systems, and their main function is to prevent backflow of the medium, prevent pumps and drive motors from reversing, and prevent the release of medium from containers. Check valves can also be used in pipelines supplying auxiliary systems where the pressure may rise above the system pressure. They are mainly divided into swing type (rotating around the center of gravity) and lift type (moving along the axis).