I am bit confused about the curve: Head Vs flow rate Curve

We could observe from the [Pump curve] that Total Head decreases with increase in flow rate, but for [System Curve], it is opposite, i.e, Total Head increases with flow rate. Why is that so? I need a detailed explanation or a link where I could understand this curve.

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    $\begingroup$ Any good textbook... also check out the dimensionless coefficients such as head, flow etc $\endgroup$ – Solar Mike Apr 14 '19 at 12:29
  • $\begingroup$ The head required to drive a given flow rate increases faster than flow rate itself - causing an uphill curve that’s getting steeper. Eventually no matter how large the head is, the flow rate won’t go any higher. $\endgroup$ – Jonathan R Swift Apr 14 '19 at 12:32
  • $\begingroup$ There are q&a on here that may help if you read them, such as engineering.stackexchange.com/q/16481/10902 $\endgroup$ – Solar Mike Apr 14 '19 at 12:34

It's quite simple:

When you're pumping a fluid, as the flow rate increases, head losses also increase. That's why the pump head decreases. As there are more internal losses, the pump provides the fluid with less energy. Pump curve: A-B*Q^2 (A and B being positive coefficients).

In the system, the increase of the flow rate increases losses as well, so the resistive head goes up. System curve: C+D*Q^2 (C and D being positive coefficients).

The operation point is the point where the pump head equates the resistive head of the system and that is true for a determinate flow rate.

  • $\begingroup$ You can edit those comments into your answer $\endgroup$ – user16 Apr 14 '19 at 15:37

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