Page 108 - Know and Understand Centrifugal Pumps

Understanding Pump Curves

NPSHr. Notice that the small drum pump doesn’t show the NPSHr.
This is because this pump, by design, can drain a barrel or sump down
to the bottom without causing problems.

To end this discussion, the curve is the control panel of the pump. All
operators, mechanics, engineers and anyone involved with the pump
should understand the curve and it’s elements, and how they relate.
With the curve, we can take the differential pressure gauge readings on
the pump and understand them. We can use the differential gauge
readings to determine if the pump is operating at, or away (to the left
or right) from its best efficiency zone and determine if the pump is
functioning adequately. We can even visualize the maintenance required
for the pump based on its curve location, and visualize the corrective
procedures to resolve the maintenance.
Up to this point, you probably didn’t understand the crucial
importance of the pump curve. With the information provided in this
chapter, and this book, we suggest that you immediately locate and
begin using your pump curves with suction and discharge gauges on
your pumps.

Get the model and serial number from your pumps, and communicate
with the factory, or your local pump distributor. They can provide you
with an original family curve, and the original specs, design and
components from when you bought the pump. A copy of the original
family curve is probably in the file pertaining to the purchase of the
pump. Go to the purchasing agent’s file cabinet.
Nowadays, some pump companies publish their family curves on the
Internet. You can request a copy with an e-mail, phone call, fax, or
letter. The curves and gauges are the difference between life and death
of your pumps. The pump family curve goes hand in hand with the
system curve, which we’ll cover in the next chapter.