Water Hammer

 

 

Water hammer (or, more generally, fluid hammer) is a pressure surge or wave resulting when a fluid in motion is forced
to stop or change direction suddenly (Momentum Change).
Water hammer commonly occurs when a valve is closed suddenly at an end of a pipeline system,
and a pressure wave propagates in the pipe.
The phenomenon is caused by the conversion of kinetic energy in a fluid to compressed-fluid energy,
according to the law of conservation of energy as described by Bernoulli's principle.
Compressed-fluid energy is equal to the mean-average pressure during compression times the change in volume.
(The work energy can also be expressed as

Where A and B are the initial and final states of the system.)
Liquids in particular are nearly incompressible, so when liquids are forced to store energy of compression,
the pressures that result are very high. The phenomenon is analogous to driving a vehicle without pneumatic tires.

 

For more info go to wikipedia