Water Hammer - Mitigating Measures

Mitigating Measures

Water hammer has caused accidents and fatalities, but usually damage is limited to breakage of pipes or appendages. An engineer should always assess the risk of a pipeline burst. Pipelines transporting hazardous liquids or gases warrant special care in design, construction, and operation.

The following characteristics may reduce or eliminate water hammer:

• Reduce the pressure of the water supply to the building by fitting a regulator.
• Lower fluid velocities. To keep water hammer low, pipe-sizing charts for some applications recommend flow velocity at or below 5 ft/s (1.5 m/s).
• Fit slowly-closing valves. Toilet flush valves are available in a quiet flush type that closes quietly.
• High pipeline pressure rating (expensive).
• Good pipeline control (start-up and shut-down procedures).
• Water towers (used in many drinking water systems) help maintain steady flow rates and trap large pressure fluctuations.
• Air vessels work in much the same way as water towers, but are pressurized. They typically have an air cushion above the fluid level in the vessel, which may be regulated or separated by a bladder. Sizes of air vessels may be up to hundreds of cubic meters on large pipelines. They come in many shapes, sizes and configurations. Such vessels often are called accumulators or expansion tanks.
• A hydropneumatic device similar in principle to a shock absorber called a 'Water Hammer Arrestor' can be installed between the water pipe and the machine, to absorb the shock and stop the banging.
• Air valves often remediate low pressures at high points in the pipeline. Though effective, sometimes large numbers of air valves need be installed. These valves also allow air into the system, which is often unwanted.
• Shorter branch pipe lengths.
• Shorter lengths of straight pipe, i.e. add elbows, expansion loops. Water hammer is related to the speed of sound in the fluid, and elbows reduce the influences of pressure waves.
• Arranging the larger piping in loops that supply shorter smaller run-out pipe branches. With looped piping, lower velocity flows from both sides of a loop can serve a branch.
• Flywheel on pump.
• Pumping station bypass.
• Hydroelectric power plants must be carefully designed and maintained because the water hammer can cause water pipes to fail catastrophically.