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How do you enter a pump curve to find its operating point?
A pump curve gives its head H against flow rate Q; it appears in the manufacturer's documentation. By reading six points from this curve, it is fitted with a polynomial H = a + b Q + c Q², which is crossed with the system curve to obtain the operating point. Two identical pumps in parallel add their flows at equal head; in series they add their heads at equal flow. Example: a pump H = 20 − 0.02 Q² (Q in m³/h) on a system H = 8 + 0.01 Q² runs at 20 m³/h and 12 m; two pumps in parallel give 28.3 m³/h at 16 m, two in series 25.3 m³/h at 14.4 m.
Pump curves and coupling
- Hpump: pump head, in m; Q: flow rate, in m³/h or m³/s
- a, b, c: coefficients fitted to the points of the manufacturer's curve
- H₁: curve of a single pump; coupling two identical pumps shifts the curve in flow (parallel) or in head (series)
- The operating point is the intersection with the system curve
Example: one pump, two in parallel, two in series
| Arrangement | Flow rate (m³/h) | Head (m) |
|---|---|---|
| One pump | 20.0 | 12.0 |
| Two pumps in parallel | 28.3 | 16.0 |
| Two pumps in series | 25.3 | 14.4 |
Detailed explanations and calculation in Mecaflux
Pump editor of mecaflux Standard:
The editor pump is located in the graphical network analysis tool.
It is possible to create a list of pumps available for research the Pump operating points of networks.
To access to the pumps editor, open the graphical analysis tool (Tools menu / internal flows / graphical analysis):
Check the "operating points of pumps".
and editor pump opens wide. You can enter the characteristics of your pump or select one from your list of pumps. The operating point of your pump, and network segment will be calculated, if you click select a network and click next.
Here we see a domestic circulator pre recorded, but at first you must enter the pumps as curves of 6 points in height load depending on the flow.
These manufacturers data are generally available on the net or in the manual supplied with the pump .. To create a new pump available in the editor select "create pump whith curve":
you're about to create your pump..
By inserting the 6 points of your "curve manufacturer" mecaflux calculate equation of your pump curve and the curve equations couplings:
For a full integration of catalog pump manufacturer, thank you to contact mecaflux :__contact@mecaflux.com___
Frequently asked questions
How many points should be read from the manufacturer's curve?
Six points spread from zero flow to maximum flow are enough to fit a centrifugal pump curve accurately. Take them from the curve matching the impeller diameter and speed of your pump.
Parallel or series: which to choose?
Parallel mainly increases the flow on a low-resistance network, series overcomes a high head. On a network with large losses, two pumps in parallel deliver only part of the expected flow, as the example shows: 28.3 m³/h instead of 40.
Where can pump data be found?
In the manufacturer's data sheet or catalogue, as a head-flow curve, often with the efficiency, power and required NPSH curves.
How do I save my pumps and calculate their operating point?
The pump editor of Mecaflux Standard, in the graphical analysis tool, calculates the curve equation from six points and the coupling curves, and saves the pump in your database with its characteristics. For a specific case, Mecaflux also offers a study of your project or training on the software.