## S 7 z2 S 7 z1 Eh12

where the subscripts 1 and 2 denote points in the pumping system anyplace upstream and downstream from the pump, respectively, and

H = total head of system, (+) or (-) ft (m) gage or (+) ft (m) abs V = velocity, ft/s (m/s)

p = pressure, (+) or (-) lb/in2 (N/m2) gage or (+) lb/in2 (N/m2) abs

Z = elevation above (+) or below (-) datum plane, ft (m)

g = specific weight (force) of liquid (assumed the same between points), lb/ft3 (N/m3)

g = acceleration of gravity, 32.17 ft/s2 (9.807 m/s2) J,hf = sum of piping losses between points, ft (m)

When the specific gravity of the liquid is known, the pressure head may be calculated from the following relationships:

In feet

In meters

The velocity in a pipe may be calculated as follows:

In feet per second V -In meters per second V -

(pipe ID in inches )2

(pipe ID in cm)2 (pipe ID in cm)2 The following example illustrates the use of Eqs. 4 and 7 for determining pump total head.

or example 1 A centrifugal pump delivers 1000 gpm (227 m3/hr) of liquid of specific gravity 0.8 from the suction tank to the discharge tank through the piping shown in Figure 8. (a) Calculate pump total head using gages and the datum plane selected. (b) Calculate total head using the pressures at points 1 and 2 and the same datum plane as (a).

Given: Suction pipe ID = 8 in (203 mm), discharge pipe ID = 6 in (152 mm), hf = pipe, valve, and fitting losses, hfs = 3 ft (0.91 mm), hfd = 25 ft (7.62 m).

In USCS units Calculated pipe velocity

In SI units

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