Handbook of Civil Engineering Calculations

Static deflection, mm

FIGURE 3. Pump shaft deflection and critical speed. (Goulds Pumps, Inc.)

Calculation Procedure:

1. Determine the deflection of the pump shaft
   Use Fig. 3 to determine the shaft deflection. Note that this chart is valid for only one
   pump or series of pumps and must be obtained from the pump builder. Such a chart is dif-
   ficult to prepare from test data without extensive test facilities.
   Enter Fig. 3 at the left at the total combined weight of the impellers, 23 Ib (10.4 kg),
   and project horizontally to the right until the weight-deflection curve is intersected. From
   the intersection, project vertically downward to read the shaft deflection as 0.009 in (0.23
   mm) at full speed.


2. Determine the critical speed of the pump
   From the intersection of the weight-deflection curve in Fig. 3 project vertically upward to
   the critical-speed curve. Project horizontally right from this intersection and read the first
   critical speed as 6200 r/min.
   Related Calculations. Use this procedure for any class of pump—centrifugal, ro-
   tary, or reciprocating—for which the shaft-deflection and critical-speed curves are avail-
   able. These pumps can be used for any purpose—process, power, marine, industrial, or
   commercial.

EFFECT OF LIQUID VISCOSITY ON

REGENERATIVE-PUMP PERFORMANCE

A regenerative (turbine) pump has the water head-capacity and power-input characteris-

tics shown in Fig. 4. Determine the head-capacity and power-input characteristics for four

Static deflection, In

Approx.

first

critical

speed,

r/min

Weight

of

combined

impellers,

N

Weight

of

combined

impellers,

(b