Technical Bulletins - A.O. Smith GPVL-50 Service Handbook

GENERAL Water hammer is the destructive force, pounding noise and vibration in a piping system when water
fl owing through a pipeline is stopped abruptly. When water hammer occurs, a high intensity pressure
wave travels back through the piping system until it reaches a point of some relief. The shock wave
will then surge back and forth between the point of relief and the point of stoppage until the destructive
energy is dissipated in the piping system. The violent action accounts for "banging", "thumping", and/or
intense vibration in the pipe line. Although noise is generally associated with the occurrence of water
hammer, it can occur without audible sound or noise. Quick closure of valves always causes some
degree of shock with or without noise. The common cause of water hammer is single lever faucets
(sinks/lavatories) or automatic solenoid valves dishwashers, washing machines, etc.). The speed of
the valve closure time is directly related to the intensity of the surge pressure.
EFFECTS The damage from water hammer can manifest itself in a number of ways. The most common are:
• Expanded Tank Shell - This can be demonstrated by measuring the circumference at various
locations along the shell. Pressures in excess of the maximum design working pressure can cause
permanent deformation of the shell. Note: The continuous expansion of the tank shell may cause
the tank to rupture at a welded seam.
• Collapsed Flue Tube - This will choke off the ability to vent the products of combustion causing
the fl ame and/or combustion to spill out from the combustion chamber. Often this will occur where
thinning of the fl ue tube walls has occurred due to contamination of the combustion air or because
of excessive condensation.
• Inverted or Deformed Tank Heads - Often this accompanies collapsed fl ues, but one or both heads
can be deformed.
THE FIX The only effective means of control is to install water hammer arrestors. These devices have
diaphragms which separate an air chamber from the water in the piping system. As the shock wave
reaches this device, the air chamber absorbs the shock. Arrestors should be located as close as
possible to the source of the shock wave.
NOTES Since water hammer exposes the equipment to pressures in excess of its design limits, failures
caused by water hammer are not eligible for warranty consideration.
SYMPTOMS • Rumbling
• Crackling
• Popping
CAUSE With the increase in fuel costs and hot water consumption, deliming has become a necessity of modern
maintenance. Lime (CaCO
present in every water system to some degree. Since lime is inversely soluble (the more you heat,
the more lime comes out), higher usage, excessive hardness, and increased heating surface can
lead to a high incidence of "limed-up" heaters. Symptoms often include a popping of water trapped
under lime deposits or the sizzling of water trapped next to elements, boiling it to steam.
THE FIX Treatment of a "limed-up" heater is relatively simple. Since CaCO
dissolve it so it can be fl ushed from the heater is with an acid. The most commonly used is phosphoric
acid at a food-grade level. Two available treatments are Mag-Erad
plumbing supply house should have a deliming solution available. The directions on the product
should be followed explicitly.
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TECHNICAL BULLETINS

WATER HAMMER
MINERAL BUILD-UP
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