Based on the method of characteristics(MOC), the mathematical model of an integrated system including the pump, pipeline, and water hammer protective measures is established in terms of a practical water supply project, and the transient pressure variation process in the system is simulated during a pump sudden stopping period. Based on simulations a low pressure exists at the local high elevation site. To avoid a negative pressure in the pipeline if an orderinary air vessel is involved in the system, then its volumme can be as large as 530.00 m3. To solve this problem, two methods, namlely, air vessel-two-way-surge tank and air vessel-one-way-surge tank, are proposed, their protective effectiveness is analyzed and compared. The results show that the volume of air vessel can be significantly reduced by two protective methods proposed. For the air vessel-two-way-surge tank method, the volume of air vessel has been reduced to 40.27 m3, however, its height reaches as high as 27.00 m, because the tank height is controlled not only by the piezometric head but also by the pump head. For the air vessel-one-way-surge tank method, the tank height is not limited by the piezometric head, and the volume of air vessel is reduced to 43.83 m3. Unforatunantely, more tanks are needed to ensure no negative pressure in the pipeline.
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