Normal and Rated Capacities
Normal and Rated Capacities
(OP)
If we select a pump by rated capacity x diff. head, how the pump operates in the same head with normal capacity (normal operating point)?
The performance curve shows that if the operating point goes from rated capacity to operating capacity (right to left in performance pump curve), the diff. head will be increased.
How does it occur in the practice?
Thanks!
The performance curve shows that if the operating point goes from rated capacity to operating capacity (right to left in performance pump curve), the diff. head will be increased.
How does it occur in the practice?
Thanks!





RE: Normal and Rated Capacities
RE: Normal and Rated Capacities
Normal capacity corresponds to the flowrate given by a PFD/Material balance.
A centrifugal pump always operates at the point on it's performance curve where its head matches the resistance in the pipeline.
In the real world, a centrifugal pump operates all over the place, depending on a flow need – and the intent is that operators will not operate the pump too far outside the recommended envelope of operation, which is typically between 70 to 120% of BEP point.
A pump curve slope generally moves upward from the duty point from right to left on the pump curve. In practice if the system head curve is underestimated and the system head is actually larger than the duty point head, the pump operating point will shift to the left along the pump curve.
http://www.gouldspumps.com/cpf_0009.html
RE: Normal and Rated Capacities
What would you be doing, if you knew that you could not fail?
RE: Normal and Rated Capacities
Another commonly used method is by varying the pump speed which changes the pump diff. head.
The intersection of the pump Q-H curve and the system curve will be the flow rate.
See attached for better understanding
RE: Normal and Rated Capacities
attachment was left out.....
RE: Normal and Rated Capacities
[2] If you have (a) a varying system curve and (b) a constant speed centrifugal pump, operation will occur along the "line" of the pump curve between the upper and lower system curves. Varying system curves are common in muncipal water systems where water levels in the storage tanks on the suction and discharge sides of the tank fluctuate and the water demands between those tanks and the pump fluctuate. This requires analyzing the system for multiple conditions, including high suction tank level to low discharge tank level, low suction tank level to high discharge tank level, and these conditions for different water demand levels and other operational issues. For some systems I have generated as many as 16 system cuves to find the actual envelope, though normally I need only 2 to 4 curves.
[3] If you have (a) a fixed system curve and (b) a variable centrifugal pump, then operation will be along the "line" of the system curve between the upper and lower operating points of the pump. I don't have any examples for this type of system.
[4] Finally, if you have (a) a varying system curve and (b) a variable centrifugal pump, then operation will within a region bounded by the upper and lower system curves and the upper and lower pump curves. This is also common in municipal water systems.
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RE: Normal and Rated Capacities