Basic Assumptions

A considerable number of assumptions were made in the derivation of the fundamental water-hammer equations and in the solution of the various hydraulic transients in pumping systems. These assumptions are often overlooked and involve the physical properties of the fluid and pipeline, the kinematics of the flow, and the transient response of the pump as follows:

1. The fluid in the pipe system is elastic, of homogeneous density, and always in the liquid state.

2. The pipe wall material or conduit is homogeneous, isotropic, and elastic.

3. The velocities and pressures in the pipeline, which is always flowing full, are uniformly distributed over any transverse cross-section of the pipe.

4. The velocity head in the pipeline is negligible relative to the pressure changes.

5. At any time during the pump transient, when operation is in the zones of pump operation, energy dissipation, and turbine operation, there is an instantaneous agreement at the pump, as defined by the steady-state complete pump characteristics of the pump speed and torque corresponding to the transient head and flow that exist at that moment at the pump.

6. The length between the inlet and outlet of the pump is so short that waterhammer waves propagate between these two points instantly.

7. Windage effects of the rotating elements of the pump and motor during the transients are negligible.

8. Water levels at the intake and discharge reservoirs do not change during the transient period.

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Survival Treasure

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