Water hammer phenomena – or hydraulic transients – occur when there is a sudden change in water flow, such as by starting or stopping pumps, or opening or closing valves in a pipeline system.

These flow changes can cause rapid pressure drops or spikes through the pipeline. Pressure spikes can easily exceed 5–10 times the working pressure of the system, placing potentially damaging stresses on the infrastructure.

Pressure drops (down to full vacuum in some cases) can cause pipelines to collapse, or surrounding groundwater to be drawn ‘back’ into the system through leaks and fittings, resulting in contamination. Repeated pressure shock cycles can damage pipes over time through material fatigue.

It is therefore critical to understand how and where hydraulic transients can form in a pipeline system, and to be able to accurately assess the maximum and minimum transient pressures that can occur. A water hammer analysis contributes to good pipeline design and optimisation (link) in mitigating this potentially dangerous occurrence.

A water hammer analysis is typically required when:

• designing liquid piping systems, to evaluate pipeline structural integrity under transient pressure conditions
• predicting pressure transients in pipelines and pumping systems under both regular operating conditions (including slamming of check valves, sudden valve closures, new streams coming online or other operating variables) and failure scenarios (such as a loss of power)
• stress testing systems with a high consequence of failure, such as those containing hazardous liquids, or causing personal safety or environmental concerns through accidental exposure
• upgrading any pumping system to change the flow capacity (such as installing a bigger pump), or required pumping head (pressure).