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Why is it not recommend to have pump shut off head lower than its operating head? Is the answer related to dropping curve by any chance? Also why is the discharge valve closed when starting the pump operation? Any help on this appreciated

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    $\begingroup$ Why is it not recommend to have pump shut off head lower than its operating head? Can you clarify what you mean by that? $\endgroup$ – idkfa Sep 11 '16 at 18:09
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To address the first point without further clarification from your side:

I think you mean unstable pump curves with that. Otherwise I wouldn't know how you could achieve a higher operating head than shut off head.

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The result would be an oscillating behavior which is not desired.

For the second part of your question the main reasons I know are

  • lower load on the driver during start up
  • avoiding recirculation if the operating pressure in the pipe is high
  • maintaining a constant pressure in the pipe, i.e. the valve is beeing opened when the discharge pressure is equal or exceeds the pipe pressure
  • avoiding a dry pump, especially if the flow on the suction can be interrupted

In general there are a lot of information on the two questions and a good book or two could prove helpful if you would like to achieve in depth knowledge. Although there should be a lot of solid information in the web too.

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