Reliant FVIR GAS WATER HEATER Technical Information PDF herunterladen (Seite 27)

BULLETIN 11

WATER HAMMER

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.

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Reliant FVIR GAS WATER HEATER Technical Information Seite 27