| Special geographical location and climatic conditions of Xinjiang, which make it more obvious for the problems about evaporation and leakage of the open channel transportation water and frost, but they also have unique advantages of developing pipes transportation water. To develop pipes transportation water, water hammer is an important safety issue, water hammer of pipe network is different from the single-tube water hammer, but more complex. From the point of view for the characteristics and advantages about Xinjiang region water-saving agriculture, this article took PVC-U as experiment pipes, studied the water hammer of transportation and distribution water for pipe network system and did numerical simulation, mainly including superposition and distribution pressure experiments of water hammer with different water distribution angles and its distance layout types, and influence of velocity and slope parameters on water hammer negative pressure.The main conclusions and findings are as follows:(1) Water distribution angles of branch have direct effect on water hammer pressure in the pipe network. With the decrease of water distribution angles, superimposed pressure values of water hammer for trunk is on the rise, which are consistent with exponential function distribution. Maximum value of superposition pressure for water hammer along the trunk are at water distribution outlet of trunk, two branch pipes water hammer are in the trunk of the collision, superimposed pressure values of trunk water hammer show decreasing distribution from maximum values to first, end of trunk pipes, and decreasing rate of upstream is larger than downstream. Water hammer pressure head of two trunk pipes show decreasing distribution from the end of branch pipe with Transient operation before valve to water distribution outlet of the first side for branch pipe. Therefore, during the pipe network design, water distribution angles of branch pipes should be larger.(2) With the increase of water distribution space, superimposed pressure values of water hammer for trunk gradually decrease, which are consistent with exponential function distribution. Maximum values of superposition pressure for water hammer along the trunk are midpoint distance of two water distribution space (in the middle points of trunk), and gradually decrease from it to first, end side of the trunk, and decreasing rate of upstream is larger than downstream. But water hammer pressure values of two branch pipes decrease from the end of branch before valve to water distribution outlet of trunk, water hammer pressure values of upstream branch is a little larger than downstream branch. Negative pressure values of water hammer gradually increase, with the increase of water distribution space. Therefore water distribution space of branch pipe should be designed opposed layout; the distance is designed as long as possible according to actual abilities of pipes restriction negative pressure.(3) With the decrease of water distribution angles, distribution pressure values of water hammer for branch gradually increase, which are consistent with exponential function distribution. Water hammer distribution pressure head of two branch pipes decrease from water distribution outlet of branch pipe to the end of branch pipe near the valve, but maximum values of water hammer pressure head along the trunk are at the end of before valve, and gradually decrease to the first side of trunk pipe with the increase of Propagation distance. Negative values of water hammer have instantaneous effect and decay quickly. Based the above theory, water distribution layout of branch pipes should be smaller; it is an optimal choice for water distribution angle as 45 degree.(4) With the increase of opposed distances for water distribution outlet, distribution pressure values of water hammer for branch gradually decrease, which are consistent with exponential function distribution.. As far as pressure distribution is concerned, water hammer pressure distribution values of the two branch pipes show decreasing distribution from branch first side to the end of branch near valve, its values of downstream for branch is a little larger than upstream. Maximum values of water hammer pressure for trunk are still at the end of trunk with Transient operation before valve, gradually decreasing from it to the first side of trunk. With the increase of opposed distances, negative values of water hammer for both trunk and branch gradually decrease. Therefore, during the pipe network design, water distribution distances should be arranged as far as possible according to the actual condition.(5) The influence of velocity parameters for pipes on negative pressure. Negative pressure of water hammer emerges periodically; its duration time also decreases periodically. With the increase of velocity, the resulting negative values of water hammer are larger, which are consistent with exponential function distribution.The longer the limit negative pressure values are, the more the number of impact for limit negative pressure is. Concerning the distribution principle along negative pressure, maximum value of negative pressure head for trunk are after valve FCV-1 of trunk first side, gradually decreasing to the end of trunk, Moreover, the decreasing rate for upstream negative pressure value of water distribution outlet with trunk is comparatively fast, but downstream is relatively slow. As for branch, maximum value of negative pressure head for branch are on the first side of branch J-8, gradually decreasing to the end of branch, decreasing rate of negative pressure for branch is obviously smaller than trunk. Taking the above conclusions into account, in order to prevent negative pressure damage, velocity in the pipes of PVC-U should be controlled within 2m/s.(6) The influence of pipes slope parameters on negative pressure of water hammer. Negative pressure of water hammer emerges periodically; its duration time also decreases periodically. Negative pressure of water hammer for both trunk and branch with different slopes have reached a limit, the steeper the slope of trunk is, the longer the duration time of limit negative pressure for water hammer with both trunk and branch is, the more the times on the pipe wall is. As far as the negative pressure friction distribution is concerned, negative pressure values of water hammer for both trunk and branch have achieved limit negative pressure value.(7) The further the distance transient source is, the smaller the water hammer pressure head is. The location of before and after the valve, elbow, raised, pipes bump and convergence superposition of water hammer, which are easy to produce water hammer pressure maximum value, but the location of negative pressure damaged is often after valve. During designing pipe network, the above areas should be designed water hammer protection devices.(8) The ability of PVC-U pipes against negative pressure shocks is very limited, pipes of nominal pressure which is 0.32～0.4Mpa are under the effect of negative pressure, it shows serious damage phenomenon while the deformation velocity is up to 10%, at the same time, which makes pipes of nominal pressure as 0.63Mpa deform, deformation degree is up to 2.5%, positive pressure value is up to 70.8m head, but it does not damage pipes. Therefore, the ability of PVC-U pipes against negative pressure shocks is relatively weak, through improving the shape of pipe sections to improve the ability of pipes resisting pipes negative pressure. |
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