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Water hammer
Water hammer


Water Hammer
By investigator Jeff

Water hammer is a phenomena that occurs when water is suddenly shut off or air is trapped in the pipes, this results as a banging, clanging sound and also may be heard as even a creaking sound . The resulting hammer can be devastating to the pipes, especially the older clay or cast iron pipes resulting in thousands of dollars in water damage , destroyed pipes appliances and surrounding areas. There have been cases in some rare instances where people have been injured or killed from the resulting explosions.

Several remedies quoted from wikipedia are as follows
  • 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 hydro pneumatic device similar in principle to a shock absorber called a 'Water Hammer Arrestor' can be installed between the water pipe and the machine, which will absorb the shock and stop the banging.
  • Air valves are often used to 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.
 
There is also a process called capitation this results from a void or bubble rapidly collapsing resulting in a sudden and violent shock wave , in fire department pumpers you see this dude to imperfect water sources this can result in the destruction of the impellers , costing thousands of dollars according to this site http://www.siouxchief.com/Resource_/ProductMedia/133/Water%20Hammer%20FAQ%204-04.pdf
 
A water hammer at only 50 psi can result in 250 – 400 psi that will not only affect the immediate area or valve that can travel back into the pipes in throughout the entire plumbing system depending on how much pressure is on the line
 
Water hammer arrestors may remedy the problem. The easiest way to prevent water hammers is simply to slowly close valves
and help minimize the effect

More info: http://en.wikipedia.org/wiki/Water_hammer