The intensity of pressure due to sudden closure of a valve of a pipe in which water flows with velocity v, is directly proportional to :

This phenomenon is known as water hammer or hammer blow. ∴ If p is density of fluid, then pressure of fluid due to water hammer is directly proportional to √p. Case – 2: Rapid closure and pipe is flexible. ∴ If p is density of fluid, then pressure of fluid due to water hammer is directly proportional to √p.