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      Burkert Contromatic (Proprietary). Ltd.
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      233 Albert Amon Road
      Millennium Business Park
      Meadowdale / Germiston

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      P.O. Box 26260
      East Rand
      1462
      Phone +27 11 574 6000
      Fax +27 11 454 1477
      E-Mail fnyrf.mn@ohexreg.pbz
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      Westville

      Phone +27 31 266 1600
      Fax +27 31 266 1495
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      Unit 26, Northgate Business Park
      Northgate Estate

      Phone +27 21 510 7137
      Fax +27 21 510 7135
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Water hammer phenomena

Valve upstream pressure as a function of time when opening or closing the valve

Zero switch-off function

The zero switch-off function ensures that the valve is closed if the input signal is less than 2 % of the maximum value. The coil current is then set to zero. The zero switch-off function must generally be deactivated to set the minimum coil current.

If the valve is suddenly closed (closing time tcl = 0) with stationary outflow at velocity w1 and if the pipe run is thus completely shut off, the fluid column is abruptly decelerated from w1 to w = 0. This produces a pressure wave which passes through the medium against the flow direction at the speed of sound "a". The pressure wave is reflected at the tank outlet (see Figure), moves back to the valve inlet and is reflected there again, etc. Superimposition of the pressure waves against the flow direction and the reflected pressure waves results in pressure piling, the maximum value of which can be calculated in accordance with the following equation:

Where:

This pressure piling in accordance with equation 10 is referred to as pressure surge or water hammer. It can be many times the operating pressure and can thus lead to bothersome noises and, above all, increased pressure stressing of the system.