Handbook of Civil Engineering Calculations

Copacity, L/8

FIGURE 2. Characteristics curves for water (solid line) and oil (dashed line). (Hydraulic In-

stitute,)

set of characteristic curves (H, g, P, E) for the pump to be used, (b) Locate the point of

maximum efficiency for the pump when handling water, (c) Read the pump capacity, Q

gal/min, at this point, (d) Compute the values of 0.6g, 0.8g, and \2Q at the maximum

efficiency, (e) Using Fig. 1, determine the correction factors at the capacities in steps c

and d. Where a multistage pump is being considered, use the head per stage (= total pump

head, ft/number of stages), when entering Fig. 1. (/). Correct the head, capacity, and effi-

ciency for each of the flow rates in c and d, using the correction factors from Fig. 1.

(g) Plot the corrected head and efficiency against the corrected capacity, as in Fig. 1.

(h) Compute the power input at each flow rate and plot. Draw smooth curves through the

points obtained, Fig. 2.

Related Calculations. Use the method given here for any uniform viscous liq-

uid—oil, gasoline, kerosene, mercury, etc.—handled by a centrifugal pump. Be careful to

use Fig. 1 only within its scale limits; do not extrapolate. The method presented here is

that developed by the Hydraulic Institute. For new developments in the method, be cer-

tain to consult the latest edition of the Hydraulic Institute Standards.

PUMP SHAFT DEFLECTION

AND CRITICAL SPEED

What are the shaft deflection and approximate first critical speed of a centrifugal pump if

the total combined weight of the pump impellers is 23 Ib (10.4 kg) and the pump manu-

facturer supplies the engineering data in Fig. 3?

Capacity, gal/min

Efficiency

Water

Water

Efficiency,%

Head,

m

Head,

ft