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Pumps and Pumping
Published in Subhash Verma, Varinder S. Kanwar, Siby John, Environmental Engineering, 2022
Subhash Verma, Varinder S. Kanwar, Siby John
A centrifugal pump must be primed or filled with water when it is started. Many pumping units have self-priming units attached to them. The foot valve is designed to prevent the suction line from emptying and to keep the pump primed. If the pump is placed below the pumping water level or suction head conditions, the pump is always primed. The pump should be started with the suction valve open and the discharge valve closed. As the motor picks up speed, the discharge valve is opened slowly. In many cases, this is an automatic operation. When shutting off the pump, the discharge valve must be closed slowly to avoid water hammer. Water hammer refers to tremendous transient pressures that can damage pipes or pumps.
Improved Pump Hydraulic Selection Extends Pump Life
Published in Heinz P. Bloch, Allan R. Budris, Pump User’s Handbook, 2021
Heinz P. Bloch, Allan R. Budris
Water hammer can be controlled through proper valve closure rates (with slow-closing valves), the addition of diaphragm tanks or similar accumulators to absorb the pressure surge, and relief valves to release the pressure.
Pumbs
Published in Béla G. Lipták, Optimization of Industrial Unit Processes, 2020
The possible methods of preventing water hammer include (1) designing the system with low velocities, (2) using valves with slow closure rates, and (3) providing slow-closing bypasses around fast-closing valves, such as check valves. When water hammer is already present and the cause of it cannot be corrected, its symptoms can be treated (1) by adding air chambers, accumulators, or surge tanks; (2) by using surge suppressors, such as positively controlled relief valves; and (3) when water flows are split or combined, by using vacuum breakers to admit air and thereby cushion the shock resulting from the sudden opening or closing of the second split stream.
Development of backward transient analysis in visco-elastic pressurized pipes
Published in Journal of Hydraulic Research, 2022
Maryam Mousavifard, Fatemeh Poursmaeili, Hamid Shamloo
The water hammer phenomenon occurs in pipelines due to sudden changes in pressurized pipe flow conditions caused by rapidly closing or opening control valves, a pump starting or stopping, etc. A pressure wave is produced that travels periodically along the pipe. The classic continuity and momentum equations that describe 1D water hammer in the pressurized pipeline read as follows (Chaudhry, 1987): where H is the instantaneous piezometric head, a is the wave speed, Q is the instantaneous flow rate, A is the cross-sectional area of the pipe, f is the Darcy–Weisbach friction factor, D is the pipe internal diameter, g is the gravity acceleration, x and t are the distance along the pipeline and time respectively.
Investigation of a new shock damper system efficiency in reducing water hammer excess pressure due to the sudden closure of a control valve
Published in ISH Journal of Hydraulic Engineering, 2020
Mohammad Bostan, Ali Akbar Akhtari, Hossein Bonakdari, Bahram Gharabaghi, Omid Noori
Using the basic principles of conservation of mass, energy, and momentum, the equations governing the water hammer phenomenon as one dimensional in the circular pipe can be extracted analytically. A pair of the partial differential equation at a time – or space dependent is obtained for the analysis of unsteady flow. By solving this differential equation, the unsteady flow in the pipes can be analysed. To address these equations, initial and boundary conditions should be specified (Chaudhry 1979). The initial conditions are obtained by considering the system’s steady-state analysis using the classical equations of fluid mechanics. Boundary conditions can also be achieved by taking into account the basic principles of conservation of mass, energy, and momentum (Chaudhry 1979). The dependent variables in the equation of water hammer are the amount of discharge and the head dependent on time and space. As analytical solution of differential equations of water hammer is very complicated (Ghidaoui et al. 2005), numerical methods such as wave plan, finite volumes, implicit characteristic lines, implicit finite difference are developed as an approximate solution alternative for solving the problem (Ghidaoui et al. 2005; Saikia and Sarma 2006; Afshar and Rohani 2008). Ghidaoui et al. (2005) reviewed all historical developments and research and practice for water hammer. Among all different approaches for solving transit flow, the method of characteristics (MOC) has an appropriate accuracy with simplicity and numerical efficiency (Ghidaoui et al. (2005)).
Computation of two- and three-dimensional water hammer flows
Published in Journal of Hydraulic Research, 2019
Simindokht SaemI, Mehrdad Raisee, Michel J. Cervantes, Ahmad Nourbakhsh
The term “water hammer” is used to describe transient flow characteristics when the flow is suddenly stopped in a closed system, e.g. a pipe network. This phenomenon produces pressure waves that travel periodically along the pipe. A water hammer most commonly occurs in piping systems, such as power plants and urban water carrier systems, due to a sudden change in the flow rate during a fast opening/closure of a valve or a pump failure. A large rise in pressure, 10 times greater than the system’s normal pressure, may cause serious damage and loss of life and property. Therefore, it is necessary to control water hammer to prevent such failures.