Silent
Check Valve
Space of the valve cavity employs
streamlined design, overcoming turbulent flow of the media.
The spherical structure at the front part
of the discs and beveled sealed surface reduce impacts on media and also the
flow -resistant coefficient.
The inner guide vane adopts
a style of thin eggshell so as to ensure the flow of the media unblocked. At
the same time, the weight of the valve reduces as well.
A largest flowing sectional area is created
by reasonably lifting the height and enlarging the inner space, which also
effectively avoid the produce of an air-chamber, upgrade the valve`s Cv value
and overcome noise.
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Abstract The advantages and disadvantages of applying duckbill valve to sea-drain project are analyzed, and the application conditions of duckbill valve in the sea-facing project are proposed. Based on the Shanghai Fengpu Paihai Project, the use of duckbill valve and multi-nozzle nozzle were compared, that the use of duckbill valve in Paihai project should be based on a comprehensive analysis of specific engineering decisions. In recent years, with the development of science and technology, the emergence of new materials, foreign countries have successfully developed a new type of valve - duckbill valve. Duckbill valve made of flexible neoprene and man-made fiber by special processing, the shape is similar to duckbill. Under the condition of no internal pressure, the duckbill exit closes under its own elasticity; as the internal pressure gradually increases, the duckbill exit gradually increases and the liquid can be discharged at a high flow rate. Duckbill valve with the current engineering commonly used flap door, Gate Valve has more advantages, has been widely used in cities, factories and pumping stations pumping water projects, in part of the sea is also used in engineering, such as the British Weymouth emissions Mouth, Hong Kong SAR New Territories discharge and other drainage projects are installed duckbill valve [1]. Based on the domestic and foreign literatures and some physical model tests, this paper briefly analyzes the advantages and disadvantages of using duckbill valves in sea drainage projects and the application conditions of the duckbill valves in discharging the sea. Advantages and Disadvantages of Using a Duckbill Valve in a Paihai Project 1.1 Advantages (1) Maintains high jet velocity. In the traditional drainage project, the nozzle orifice is a fixed orifice, and the nozzle jet flow rate increases linearly with the increase of flow rate. When the discharge orifice discharge is small, the nozzle orifice flow velocity is low. The outlet area of ​​the orifice valve increases with the increase of discharge Big. Therefore, when the discharge is small, the jet flow rate increases rapidly. When the flow rate increases to a certain value, the increase of the jet velocity tends to be linear with the increase of the flow rate. Fig. 1 shows the comparison of the jet velocity changing with the increase of discharge when the fixed orifice and the duckbill valve are installed on the single-hole discharge port under the same conditions. It can be seen from Fig. 1 that the jet speed after installation of the duckbill valve is obviously higher than the jet speed of the fixed jet, and the jet with the duckbill valve can still have a higher jet velocity when the discharge volume is lower. Fig.1 Comparison of jet velocity between fixed orifice and duckbill valve for single orifice venting (2) Preventing seawater and sediment invasion. There is a certain density difference between the seawater and the discharge of sewage. When the discharge of sewage is small, the conventional discharge diffuser will decrease due to the jet velocity of the nozzle. This density difference will cause the seawater to invade the diffuser and bring the seabed sediment into diffusion Device [3]. The outlet of the duckbill valve changes with the change of outlet flow, closes when the discharge volume is zero, and maintains the high jet velocity when the discharge volume is low, thus preventing the invasion of seawater and environmental sediment. (3) is conducive to discharge pipe flushing. The diffuser is filled with seawater when it is used for a period of time after the discharge port is first operated or when it is not used for a period of time. In the case of a conventional discharge pipe, when the flushing flow is gradually increased, the sewage is generally discharged from the first riser near the shore, The ascending tube will cause seawater to flow backwards to form seawater circulation in the diffuser. Only when the amount of sewage discharged reaches a certain value, the ascending tube will gradually start to discharge all the sewage and remove the seawater in the diffuser tube [4]. When the duckbill valve is installed on the discharge pipe, the sewage can be discharged from all the riser pipes when the discharge amount is very small under the same conditions. With the increase of the discharge volume, the seawater at the bottom of the pipe is gradually sucked and discharged. (4) Under certain conditions, get a higher dilution. The model tests on the single nozzle diffuser with the same environmental conditions show that the installation of the duckbill valve achieves a higher degree of dilution of the sewage than that of the fixed nozzle when the horizontal jet flows in the same direction [1]. (5) Do not corrode. For less commonly used vents, such as emergency vents, it may be necessary to have a moving door or other backflow prevention device on the vents. However, the long-term submersion of metal components in the seawater can easily lead to rust and the multiplication of marine organisms, preventing the discharge ports from operating normally and causing inconvenience to maintenance. Duckbill valve is processed by special rubber processing, to avoid the threat of corrosion. 1.2 Disadvantages (1) increase project costs. Because duckbill valve processing technology is complex, only a small number of manufacturers in the world can produce products that meet the requirements of use, and customized according to the specific project, so the price is expensive. (2) increase the diffuser head loss. Figure 2 for the same conditions single orifice vent fixed orifice and duckbill valve head loss comparison chart. Can be seen from Figure 2, the installation of duckbill valve head loss is basically installed fixed spout 2 times, thus increasing the energy consumption of the discharge port, an increase of perennial operating costs. Fig.2 Comparison of the head loss between a fixed orifice and a duckbill valve with a single hole discharge port 1.3 Applicable Conditions of a Duckbill Valve in Paihai Project The application of the duckbill valve in discharging the sea should be determined through analysis according to the specific engineering features. Based on the domestic and international researches and the results of model tests conducted by Tongji University for many years [5-6], it is considered that the problems of seawater and environmental sediment invasion and flushing often appear under the following conditions: (1) the density difference between seawater and discharged sewage is large; (2) ) Riser height is larger; (3) Outflow density Froude number is smaller. For the density difference between sewage and seawater is relatively small and the height of riser is lower, if there is reasonable design and long-term normal operation, seawater and environmental sediment intrusion generally do not occur and there is no problem in flushing. Based on the above analysis, taking into account the project cost and long-term operating cost factors, the application conditions of the duckbill valve in the sea-drain project are as follows: (1) the deep water discharge port with larger density difference between sewage and seawater and the riser height is higher; (2) Discharge outlets that are not operated regularly, such as emergency discharge ports. 2 Fengpu Paihai project application duckbill valve 2.1 Analysis of the original design Fengpu Paihai project is the use of pipe jacking tunnel tunnel construction, the diffuser length of 200m, diameter 1.6m, set up 14 risers , Riser pipe diameter of 23.9cm, rising tube diffuser centerline height of about 7.0m ~ 8.0m between. The original design uses a duckbill valve, due to cost factors, the original design intends to install a duckbill valve on each riser; duckbill valve with an elbow bend cost about twice without the elbow, Therefore, the same cost factor, the design uses a duckbill valve without elbow, that is, the duckbill valve spout vertical upward. The discharge of Hangzhou Bay waters with low salinity, salinity of 10% to 20% in February the highest annual salinity, the lowest for the year in August, but the annual range of salinity is small, 0.3% ~ 0.4%. From the salinity value of the situation we can see that the discharge of sewage and sea water density difference is relatively small. 2.2 Application Duckbill valve and multi-nozzle nozzle comparison Duckbill valve characteristics and applicable conditions can be seen that the application of duckbill emergency discharge port valve is necessary and reasonable. The following is only the normal discharge port duckbill valve for some analysis, the analysis of the current domestic and international similar to the common row of risers to install multi-nozzle (jet angle of the basic level) nozzle discharge for comparison. Application Duckbill valve program according to the project acceptable level of consideration, that is, each riser to install a single vertical duckbill valve. (1) Dilution and diffusion of sewage. When the duckbill valve is installed upright on the ascending pipe, the water flow rate increases due to the shallow water environment. The sewage has not yet been fully diffused to reach the water surface, which is not conducive to the dilution of the sewage. According to the model test, it is found that the jet of water quickly rushes to the surface of the water, causing the instability of the vertical flow regime, resulting in a pronounced roll phenomenon (as shown in Figure 3). The mixed effluent is brought back into the circulation due to the vertical circulation Plume participation in the new blend, affecting the initial dilution. After physical model test and mathematical model calculations show that when the duckbill valve is installed vertically upward, the dilution when the sewage rises to the water surface is only about 10. In the ascending pipe, a multi-jet nozzle is installed, and the jet of water is discharged horizontally from the jet nozzle to increase the mixing of the sewage and the environmental head, which is beneficial to the dilution and diffusion of the sewage. It is the best form that the sewage is considered suitable for the drainage of shallow water in recent years. According to the physical model test and mathematical model calculation, when the project installs multi-nozzle nozzle, the dilution of the sewage up to the water surface can reach 200-250. Figure 3 Duckbill valve mounted vertically upward when the water formed in the roll phenomenon (2) to prevent the invasion of sea water and environmental sediment. The use of duckbill valve can effectively prevent sea water and environmental sediment invasion. Multi-jet diffuser in order to prevent the invasion of sea water and environmental sediment, requires the jet density Froude number greater than 1 [6]. For this project, as the density difference between seawater and sewage is small, riser height is not large, as long as the diffuser design is reasonable, the discharge volume is normal, the general jet density Froude number is far greater than 1, will not happen seawater and environmental sediment Intrusion, and discharge pipe washing is also no problem. (3) diffuser tube deposition. According to experimental studies, the use of duckbill valves makes riser pipe flow more uniform along the way, which is advantageous for deep-water outlets and more in line with the general design requirements for deepwater discharge. However, when the sediment concentration in the sewage is high and the discharge amount is small, it is easy to form serious sedimentation or clogging due to the small flow velocity in the diffuser's tail pipe. The use of multi-nozzle sprinklers in the design and operation of the management can be flexible measures, such as the riser uneven distribution nozzle (the ascent riser than the number of nearshore) or plug the offshore riser nozzle can increase Diffuser tail section of the flow rate, reducing siltation thickness to prevent sediment silting. (4) head loss. The discharge port using a duckbill valve increases the head loss due to the increased local resistance coefficient of the outlet, and the increase of the head loss does not increase by 2 times as compared with that of the discharge port using the multi-jet nozzle The head loss value is also considerable. Because of the increase of head loss, it is required to increase the height of the upper well and increase the lift of the pump, thus increasing the project cost and annual running cost. (5) repair and maintenance. According to factory data, duckbill valve due to avoid corrosion, long-term use, generally do not need maintenance and repair. Multi-nozzle nozzle discharge if the design is reasonable (consider anti-corrosion measures), and can maintain normal operation, generally do not need maintenance and repair. Such as Shanghai Chuk Yuen discharge (in December 1993 through the water), Shanghai Spark Development Zone vent (March 1993 operation), in 1998, respectively, diving inspection and remove the nozzle inspection and found normal operation of the nozzle without corrosion , There is almost no parasitic marine life at the spout [7]; foreign data also show that there is no problem of parasitic sealing of the spout by marine organisms at the discharge port that can maintain normal operation [7]. (6) project cost and operating costs. Duckbill valve itself is expensive, plus an additional head loss, then the project cost and perennial operating costs, the use of duckbill valve than the use of multi-nozzle nozzle to be higher. In summary, Fengpu Paihai project according to the original design options using the duckbill valve more harm than good, you can consider the use of multi-nozzle nozzle replaced. Even if the duckbill valve is used, the design of the duckbill valve in the original design should be further adjusted, such as increasing the number of duckbill valves and changing the direction of the duckbill valve to the horizontal so as to fully utilize the advantages of the duckbill valve. 3 Conclusion drainage project using duckbill valve, with the prevention of sea water and sediment invasion, conducive to the discharge pipe flushing, under certain conditions, improve the dilution of the sewage and corrosion resistance and strong, suitable for sea water and sewage density difference, And the riser height of the larger discharge port can also be used for less commonly used emergency discharge port. Because the duckbill valve has the advantage of increased project costs and head loss in exchange for, so the drainage of the project on the duckbill valve application should be carefully considered, should be based on a comprehensive analysis of the specific advantages and disadvantages of the project to determine the use or not. Search Keyword: More Valve Technical Articles