Methods to Protect Gravity Flow Pipeline in Hilly Area Affected by Water Hammer

Abstract

【Background and Objective】 Gravity-driven pipelines have low impact on geological environment, low leakage, simple construction and low operation cost. They have been widely used in irrigation and water supply projects. When the end valve is suddenly turn off under unpredicted circumstances, however, it could result in water hammer and pressure vibration in the pipelines, threating safe operation of the system. Considering water hammer is more likely to occur in long-distance gravity flow pipeline in hilly areas, this paper explore efficacy of different methods to ameliorate the damaging effect of water hammer on gravity flow pipeline in hilly areas. 【Method】 The study is based on the gravity pipeline project in Qianyang County, Shaanxi province. Numerical simulation combined with inclined straight pipes and fitted equivalent short straight pipe is used to simulate the protective effect of setting inlet and exhaust valve in each hump section and an overpressure relief valve in the front of the end control valve section. We analyzed the simulation results to determine the effect of these methods in alleviating water hammer at specific locations in the pipelines. 【Result】 Without the water hammer protection measure, when the control valve at the end of the pipeline is turn off quickly, there is no noticeable negative pressure along the pipeline; the maximum negative pressure head reaches - 20.06 m, and the maximum positive pressure at the section of the control valve at the end of the pipeline reaches 87.58 m. Installation of the water hammer protection measures eliminates the occurrence of negative pressure in the pipeline and reduces the maximum positive pressure head in the pipeline to 70.88 m, which is lower than the critical pressure for occurrence of water hammer in the pipelines. 【Conclusion】 For the gravity-driven water transmission pipeline in hilly areas, combination of inlet and exhaust valve and an over-pressure relief valve can effectively alleviate the occurrence of water hammer and ensure that the pressure in the pipeline is less than the critical pressure required in the design of the pipelines.

Keywords

• hilly area
• gravity flow pipeline water conveyance
• water hammer protection
• numerical simulation
• inlet and exhaust valve
• over-pressure relief valve