Internal shock, or pressure surge, known commonly as water hammer results from abrupt change of fluid velocity within the system. Under certain conditions, these shock forces can reach magnitudes sufficient to rupture or collapse a piping system, regardless of the material of construction. The transient pressure is the rapidly moving wave that increases and decreases the pressure in the system depending on the source of the transient and direction of wave travel.

Rapid valve closure can result in the buildup of shock waves due to the conversion of kinetic energy of the moving fluid to potential energy that must be accommodated. These pressure waves will travel throughout the piping system and can cause damage far away from the wave source.
The magnitude of water hammer is a function of the fluid properties and velocity, the modulus of elasticity and wall thickness of the pipe material, the length of the line, and the speed in which the momentum of the fluid changes. The relatively high compliance (low modulus of elasticity) of fiberglass pipe contributes to a self damping effect as the pressure wave travels through the piping system. The magnitude of the pressure wave in a metallic piping system is much higher due to the higher modulus of elasticity of these materials.
In addition to rapid valve closure or opening, sudden air release and pump start-up or shut-down can create water hammer. Water hammer pressure surges do not show up readily on conventional tube pressure gauges because of the slow response of the instrument. The net result of water hammer can be excessive pressures, pipe vibration, or movement that can cause failure in pipe and fittings.

Surge Analysis

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