Hydraulics and Fluid Mechanics in ME
The hammer blow in pipes occurs when

The flow of fluid through the pipe is suddenly brought to rest by closing of the valve
The flow of fluid through the pipe is gradually brought to rest by closing of the valve
There is excessive leakage in the pipe
The pipe bursts under high pressure of fluid

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Hydraulics and Fluid Mechanics in ME
For similarity, in addition to models being geometrically similar to prototype, the following in both cases should also be equal

all the four ratios of inertial force to force due to viscosity, gravitation, surface tension, and elasticity
ratio of inertial force to force due to gravitation
ratio of inertial force to force due to surface tension
ratio of inertial force to force due to viscosity

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