Advantages and disadvantages of various types of valves: gate valves, butterfly valves, ball valves, globe valves, plug valves, safety valves, steam traps, pressure relief valves, check valves

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This post was last edited by foam_ZPTK on 2019-8-17 at 11:08. Selection and Installation Locations of Valves (I) Principles for Selecting Valves Used in Water Supply Pipes 1. When the pipe diameter is 50 mm or less, globe valves are preferred; for diameters larger than 50 mm, gate valves and butterfly valves are suitable. 2. Regulating valves and globe valves are appropriate when it is necessary to control flow rate or water pressure. 3. Gate valves are suitable for sections where low water flow resistance is required (such as on the suction pipes of water pumps). 4. Gate valves and butterfly valves should be used in sections where water flow needs to occur in both directions; globe valves should not be used in such cases. 5. Butterfly valves and ball valves are suitable for areas with limited installation space. 6. Globe valves are appropriate for sections that are frequently opened and closed. 7. Multi-functional valves are suitable for the outlet pipes of water pumps with larger diameters. (II) Locations for Installing Valves in Water Supply Pipes 1. In residential area water supply pipes, they are installed starting from the connection point with the municipal water supply pipes. 2. At the nodes of the outdoor ring network in residential areas, valves should be installed according to the requirements for separation. When the length of a looped pipe section is excessive, it is advisable to install sectional valves. 3. At the beginning of branch pipes extending from the main water supply pipe in residential areas, or at the start of service pipes leading to individual households. 4. On inlet pipes, water meters, and all branch risers (at the bottom of risers, as well as at the upper and lower ends of vertical pipes within looped networks). 5. On sub-main pipes within looped networks, as well as on connecting pipes linking to dendritic networks. 6. At the start of distribution pipes branching off from indoor water supply systems toward residences, public restrooms, etc.; such valves should be installed when there are three or more water outlets along a distribution branch pipe. 7. On discharge pipes of water pumps, as well as on suction pipes of self-priming pumps. 8. On inlet, outlet, and drain pipes of water tanks. 9. On make-up water inlet pipes for equipment such as heaters and cooling towers. 10. On distribution pipes supplying water to sanitary fixtures like toilets, urinals, washbasins, and showerheads. 11. Before certain accessories—such as automatic air vents, pressure relief valves, water hammer arresters, pressure gauges, fire hydrants, etc.—and on both sides of pressure reducing valves and backflow preventers. 12. A drain valve should be installed at the lowest point of the water supply network.
(III) Selection of check valves
Check valves should generally be selected based on factors such as their installation location, water pressure upstream of the valve, required level of tightness after closure, and magnitude of water hammer generated upon closure:
1. When water pressure upstream of the valve is low, swing-type, ball-type, or shuttle-type check valves are preferred.
2. When strict tightness after closure is required, check valves equipped with closing springs should be chosen.
3. To mitigate water hammer upon closure, quick-closing silent check valves or slow-closing check valves fitted with damping devices are recommended.
4. The flap or disc of a check valve must be capable of closing automatically under the influence of gravity or spring force.
(IV) Installation of check valves on water supply pipes
On service inlet pipes ； On the inlet pipe of a sealed water heater or water-related equipment ； On the water pump outlet pipe ； On the outlet pipe section of water tanks, water towers, and elevated water reservoirs that use a single pipe for both inlet and outlet water. Note: Pipe sections equipped with pipe check valves do not require a check valve to be installed. (5) Locations for installing exhaust devices in water supply pipes: 1. In water supply networks that are used intermittently, automatic exhaust valves should be installed at the ends of the network as well as at its highest points. 2. In sections of the water supply network where air tends to accumulate due to fluctuations in pressure, automatic exhaust valves or manual valves should be installed at the peak points of those sections. 3. In pressure-driven water supply systems, when automatic air replenishment tanks are used, automatic exhaust valves should be installed at the highest points of the distribution network. Advantages and disadvantages of various valves: 1. Gate valves are valves in which the closing element (gate) moves vertically along the axis of the pipe. They are primarily used in pipelines to shut off the flow of fluid, either by fully opening or fully closing them. Generally, gate valves cannot be used to regulate flow. It can be used in low-temperature and low-pressure conditions as well as in high-temperature and high-pressure conditions, and it can be adapted to different valve materials. However, gate valves are generally not used in pipelines for transporting media such as slurry. Advantages: ① Low fluid resistance ； ②The torque required to open and close is low ； ③It can be used in ring piping systems where the medium flows in both directions; in other words, the flow direction of the medium is not restricted ； ④When fully open, the sealing surface is subject to less erosion by the working medium compared to a globe valve ； ⑤The structural form is relatively simple, and it has good manufacturability ； ⑥The structural length is relatively short. Disadvantages: ① It has large external dimensions and opening height, requiring a substantial amount of space for installation ； ②During the opening and closing process, relative friction occurs between the sealing surfaces, resulting in significant wear; in addition, high temperatures can easily lead to scuffing ； ③Generally, gate valves have two sealing surfaces, which adds some difficulties to processing, grinding, and maintenance ； ④The opening/closing time is long. 2. Butterfly valve: A butterfly valve is a type of valve that uses a disc-shaped valve element to rotate back and forth by about 90° in order to open, close, or regulate the flow of fluid. Advantages: ① Simple structure, small size, light weight, low material consumption; not suitable for large-diameter valves ； ②Rapid opening and closing, low flow resistance ； ③It can be used in media containing suspended solid particles, and depending on the strength of the sealing surface, it can also be used for powdered and granular media. It can be used for two-way opening, closing, and adjustment in ventilation and dust removal pipelines, and is widely applied to gas pipes and water pipelines in metallurgy, light industry, power, and petrochemical systems. Disadvantages: ① The flow regulation range is limited; when it is set at 30%, the flow rate exceeds 95% ； ②Due to the structure of butterfly valves and the limitations of their sealing materials, they are not suitable for use in high-temperature and high-pressure piping systems. The normal operating temperature is below 300°C, and the pressure rating is below PN40 ； ③Its sealing performance is inferior to that of ball valves and globe valves, so it is used in applications where high sealing requirements are not necessary. 3. Ball valve: The ball valve evolved from the plug valve; its closing element is a sphere, and opening and closing are achieved by rotating this sphere 90° around the axis of the valve stem. Ball valves are primarily used on pipelines to shut off, distribute, and change the direction of fluid flow; those designed with a V-shaped opening also possess excellent flow regulation capabilities. Advantages: ① It has the lowest flow resistance (actually 0) ； ②It does not get stuck during operation (without lubricant), allowing it to be reliably used in corrosive media and low-boiling-point liquids ； ③Complete sealing can be achieved over a wide range of pressures and temperatures ； ④Fast opening and closing can be achieved; the opening and closing time for certain structures is as low as 0.05–0.1 seconds, ensuring their suitability for use in automated systems on test benches. When the valve is opened and closed quickly, the operation is shock-free ； ⑤The spherical closure element can automatically position itself at the boundary position ； ⑥The working medium is reliably sealed on both sides ； ⑦When in the fully open and fully closed positions, the sealing surfaces of the ball and the valve seat are separated from the medium, so the medium flowing through the valve at high speeds does not cause erosion of these sealing surfaces ； ⑧With its compact design and low weight, it can be considered a suitable valve structure for low-temperature medium systems ； ⑨The valve body is symmetrical; especially in the case of welded valve bodies, it can effectively withstand the stresses exerted by the pipes ； ⑩The closing element can withstand the high pressure difference during closure. ⑾Ball valves with fully welded valve bodies can be buried directly underground, preventing the internal components of the valve from being corroded; their service life can reach 30 years, making them the ideal valves for oil and gas pipelines. Disadvantages: ① Since the main sealing material for ball valves is polytetrafluoroethylene, it is inert to almost all chemicals. It also possesses a number of advantages, including a low friction coefficient, stable performance, resistance to aging, a wide temperature range of operation, and excellent sealing properties. However, the physical properties of polytetrafluoroethylene, including its high coefficient of expansion, sensitivity to cold flow, and poor thermal conductivity, require that the design of the valve seat seal take these properties into account. Therefore, when the sealing material hardens, the reliability of the seal is compromised. Moreover, polytetrafluoroethylene has a low temperature resistance and can only be used at temperatures below 180°C. Above this temperature, the sealing material will age. When considering long-term use, it is generally not used at 120°C. ②Its regulating performance is somewhat inferior to that of globe valves, especially pneumatic valves (or electric valves). 4. A globe valve is a type of valve in which the closing element (valve disc) moves along the center line of the valve seat. Based on this manner of movement of the valve disc, the change in the valve seat opening is directly proportional to the stroke of the valve disc. Due to the relatively short opening and closing stroke of the valve stem in this type of valve, as well as its highly reliable shut-off function, and because the change in the valve seat orifice is proportional to the stroke of the valve disc, it is very suitable for regulating flow rate. Therefore, this type of valve is very suitable for use in cutting off or regulating flow, as well as for throttling. Advantages: ① During opening and closing, the frictional force between the valve disc and the sealing surface of the valve body is lower than that of gate valves, thus it is more wear-resistant. ②The opening height is generally only 1/4 of the valve seat passage, so it is much smaller than gate valves ； ③Typically, there is only one sealing surface on both the valve body and the valve disc; therefore, the manufacturability is relatively good, and maintenance is easy ； ④Due to its filler, which is generally a mixture of asbestos and graphite, it has a high temperature resistance rating. Gauge valves are generally used for steam valves. Disadvantages: ① Due to the change in the flow direction of the medium as it passes through the valve, the minimum flow resistance of globe valves is also higher than that of most other types of valves ； ②Due to the long travel distance, its opening speed is slower than that of a ball valve. 5. Plug Valve: A plug valve is a rotary valve whose closing element is in the form of a plunger; it operates by rotating 90° to connect or separate the passage in the plunger from the passage in the valve body, thereby enabling opening or closing. The shape of the valve plug can be cylindrical or conical. Its principle is basically similar to that of a ball valve, which was developed from a plug valve. It is primarily used in oil field extraction, as well as in the petrochemical industry. 6. Safety valve: A safety valve is a device used as an overpressure protection mechanism in pressurized containers, equipment, or pipelines. When the pressure inside a device, container, or pipeline rises above the allowable level, the valve opens automatically, allowing for complete discharge in order to prevent further increases in pressure within that device, container, or pipeline ； When the pressure drops to the specified value, the valve should close automatically and promptly, thereby ensuring the safe operation of the equipment, containers, or pipelines. 7. Steam traps: When transporting media such as steam and compressed air, some condensate water is formed. To ensure the efficiency and safe operation of the equipment, it is necessary to remove this unnecessary and harmful material promptly, so as to maintain optimal performance of the equipment. It has the following functions: ① It can quickly remove the condensed water that is generated ； ②Prevent steam leakage ； ③Remove air and other non-condensable gases. 8. Pressure reducing valve: A pressure reducing valve is a valve that reduces the inlet pressure to a desired outlet pressure through regulation, and relies on the energy of the medium itself to maintain the outlet pressure stable automatically. 9. Check valve A check valve is also known as a backflow valve, non-return valve, backpressure valve, and one-way valve. These valves open and close automatically due to the force generated by the flow of the medium itself within the pipeline; they are a type of automatic valve. Check valves are used in piping systems; their main functions are to prevent backflow of the medium, to stop the pump and driving motor from rotating in reverse, and to allow the release of medium from containers. Check valves can also be used in pipelines that supply auxiliary systems whose pressure may rise above the system pressure; they can mainly be divided into swing type (rotating around its center of gravity) and lift type (moving along its axis).