Calculation of stop water hammer and its protective measures

Abstract: This paper briefly introduces the calculation basis of stopping water hammer and uses computer software to simulate the working condition of stopping water hammer of actual project. According to a number of projects and computer simulation results, proposed pumping station and pipeline design should pay attention to the problem and stop pump water hammer protection measures. Keywords: stop pump, water hammer, calculation, protective measure, stop pump, water hammer, is a kind of water hammer phenomenon, refers to the water pump and the pipeline suddenly stopped due to sudden power failure or other reasons caused by the open valve state System, due to a sudden change in flow rate caused by a series of dramatic pressure alternating hydraulic lift phenomenon. Under normal circumstances, the most serious pump stop water hammer, which has a great threat to the safety of pumping stations and pipelines, there are several domestic pumping station water pump has occurred and lead to pump house submerged or pipeline rupture of a major accident. Pump stop water hammer size and pump room in the water pipeline and the specific circumstances. In the pump room and water pipeline design should take into account the water hammer may occur, and take appropriate precautions to prevent the occurrence of water hammer, or the impact of water hammer control within the allowable range. Based on the latest achievements in research on water hammer at home and abroad, combining with the experiences of many years of engineering practice, our hospital developed the water hammer calculation program based on the characteristic line method. This procedure can well simulate the water hammer condition of water pump and water pipe system under various working conditions and provide the design basis for high-lift long-distance water conveyance project. 1, stop pumping theory calculation of water hammer to stop the calculation of water hammer there are a variety of ways: graphic method, the number of solutions and electrical algorithms. Its basic principle is to establish the equations of motion and continuous equations of water hammer process according to the theory of elastic water column. These two equations are hyperbolic partial differential equations. The equation of motion is: Continuous equation is: Where: H - the head of a point in the tube V - the flow velocity in the tube a - the velocity of water hammer wave propagation x - the coordinates of a point in the pipeline g - the acceleration of gravity t - Time f - Pipe Friction Factor D - Pipe Diameter The most important basic equation for water hammer analysis and calculation is obtained by simplified solution: H-H0 = F (t-x / a) + F V - V0 = g / a × F t - x / a - g / a × F t + x / a where F (t- x / a) - direct wave F (t + x / a) - Reflected waves In the wave theory, the direct and reflected waves propagate in the coordinate axes (H, V) in the form of rays, ie characteristic lines. It shows the pipe at a certain point in the process of water hammer at the corresponding moment of head H and the relationship between flow velocity V. In order to facilitate the calculation of the computer, the above equation system is transformed into a head balance equation and a speed change equation, that is, two boundary condition equations of the pump when the pump is stopped: F1 = PM-BQv + Hn (β2 + v2) (A0 + A1x) -ΔH0v2 / ) = 0 (5) F2 = (β2 + v2) (B0 + B1x) + m0-C3 (β0- β) = 0 where β - N / Nn is the actual speed / rated speed v - Q / Qn Flow / Nominal Flow) Using the Newton-Raphson iterative formula, the approximate values ​​of v and β can be solved by the simultaneous formulation of the above two equations. The overall performance curve of the water pump is transformed into a comprehensive performance curve related only to the speed and the flow rate so that the computer takes values ​​when solving the equation: WH (x) = h / (β2 + v2) (7) WM (x) = m / (β2 + v2) where h - H / Hn (actual lift / nominal lift) m - M / Mn (actual torque / rated torque) The current water hammer calculation method is based on the above principle. Simulation results of waterhammer conditions under several boundary conditionsAccording to the actual situation of water pump and water pipeline in a city pumping station in South China, the computer simulation of water hammer is as follows (all based on the lowest dry water level): Basic situation :