Page 108 - Centrifugal Pumps Design and Application

NPSH 89

Figure 8-4. Pressure loss between suction nozzle and leading edge of impeller
vane.

constant and varying the capacity, or by holding the speed constant and
reducing the suction pressure at various capacities. Either of these meth-
ods will produce a breakdown in the head characteristic as shown in Fig-
ure 8-5, indicating a condition under which the performance of the pump
may be impaired.
Accurately determining the inception of cavitation requires extreme
control of the test and involves sophisticated instrumentation. The Hy-
draulic Institute has permitted a drop in head of 3 % to be accepted as

Figure 8-5. Loss in head during cavitation test.