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The Practical Pumping Handbook ~ iiiiii:

Therefore when Cavitation occurs in a pump, there are only two
possible solutions:
9 Decrease the NPSH Required, or

9 Increase the NPSH Available.
In exploring possible cures for cavitation, it is interesting to note that
(unless there has been a major selection or design flaw) most pumps
cavitate because there is a pressure differential between the NPSHA and
the NPSHR of less than a few feet. Consequently it is seldom necessary
to make a major change to eliminate the problem.

4.4.1 NPSH Required by the pump
For well over 20 years every reputable Pump Manufacturer has
conformed to a single testing standard to establish the NPSH required
by a pump. That standard identifies the value of the Net Positive
Suction Head required by the pump based on a 3% head drop. In other
words, it is that amount of energy supplied to a pump that creates a
reduction in the Total Head of no more than 3%. These factory tests
are conducted at a constant flow rate in accordance with the Standards
of the Hydraulic Institute and result in a curve similar to that shown in
Figure 4.3.
A few specialty pumps in extremely critical applications are sometimes
required to identify the NPSH required for a 1.0% head drop. On even
more rare occasions the NPSH required at the 'Incipient Cavitation'
point, is requested. This latter condition is essentially at that point
where the first bubble can be heard imploding through special audio
equipment. It should be stressed that these are not the standard 'off-

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NPSH Reqd.

Figure 4.3. NPSH at constant fl0w rate