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# Water Hammer

Posted in Hydraulics |  Email This Post |

Water hammer is a change in pressure, either above or below the normal pressure, caused by a variation of the flow rate in a pipe.

The equation for the velocity of a wave in a pipe is

U=?(E/?)?[1/(1+ED/Ept)]

where
U =velocity of pressure wave along pipe, ft /s (m/s)

E =modulus of elasticity of water, 43200000 lb/ft2
(2070000 kPa)

D =diameter of pipe, ft (m)

Ep =modulus of elasticity of pipe material, lb/ft2
(kg/m2)

t =thickness of pipe wall, ft (m)

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• Andrew Timms October 30, 2009 at 4:39 pm

How does the equation for water hammer surge pressure take into account the mass of the fluid being stopped? I would think that the greater the body of water being stopped the greater the pressure. yet the formula only seems to consider the change in velocity regardless of the mass of fluid being stopped. Can someone help me understand this a litte better please.

Regards, Andrew Timms

• Ryan April 19, 2011 at 7:52 am

Bc the if you go through the derivation of the above formula the mass of the water is removed.