What is water hammer?
Water hammer is a term that has many names, such as fluid hammer, hydraulic transients, fluid transients or surge. Regardless of the name used, it is a condition that occurs in liquid piping systems when there is a transient event that causes departure from steady state, such as sudden valve closure, pump speed changes, tank pressurization, sudden power failure or other events that cause a sudden change in pressure or flow.
The transient event results in a pressure wave traveling along the piping system and reflecting back. The resulting system pressure will be above or below the steady state pressure depending on the location in the system and time from transient event. The speed of the transient wave depends on the liquid acoustic velocity, density and modulus of elasticity, pipe modulus of elasticity, wall thickness, Poisson’s ratio and the pipe restraints.
Water hammer commonly occurs in liquid piping systems but may not be noticed in cases where the transient pressure wave is less notable; however, there have been many instances where water hammer has resulted in the pressure wave exceeding pressure limits, resulting in ruptured or damaged system components due to pressure above steady conditions and vaporization of the liquid when the pressure wave results in a negative pressure.
The piping system designer should consider the potential causes and effects of water hammer in the system and implement proper mitigation techniques when required.
For more information on water hammer, refer to American National Standards Institute/Hydraulic Institute (ANSI/HI) 9.6.6 Rotodynamic Pumps for Pump Piping and HI’s suite of training covering the topic of water hammer at pumps.org.
