Page 411 - Civil Engineering Formulas

338 CHAPTER TWELVE

PUMPS AND PUMPING SYSTEMS

Civil engineers use centrifugal and other rotating pumps for a variety of
tasks—water supply, irrigation, sewage treatment, fire-fighting systems, ship
canals—and numerous other functions. This section of Chap. 12 presents per-
tinent formulas for applying rotating pumps for these, and other tasks.
Reciprocating-pump formulas are excluded because such pumps do not find
major usage in large civil-engineering projects. Their prime usage is as meter-
ing and control dispensers in sewage treatment. The formulas given in this
section are the work of Metcalf & Eddy, Inc., written and edited by George
Tchobanoglous, Professor of Civil Engineering, University of California,
Davis, at the time of their preparation.

Capacity
The capacity (flowrate) of a pump is the volume of liquid pumped per unit of
time, which usually is measured in liters per second or cubic meters per second
(gallons per minute or million gallons per day).

Head
The term head is the elevation of a free surface of water above or below a ref-
erence datum.
In pump systems, the head refers to both pumps and pump systems having
one or more pumps and the corresponding piping system. The height to which
a pump can raise a liquid is the pump head and is measured in meters (feet) of
the flowing liquid. The head required to overcome the losses in a pipe system
at a given flowrate is the system head.
Terms applied specifically to the analysis of pumps and pump systems
include (1) static suction head, (2) static discharge head, (3) static head, (4)
friction head, (5) velocity head, (6) minor head loss, and (7) total dynamic
head, which is defined in terms of the other head terms. Each of these terms is
described in the following and is illustrated graphically in Fig. 12.28. All the
terms are expressed in meters (feet) of water.

Static Suction Head. The static suction head h is the difference in elevation
s
between the suction liquid level and the centerline of the pump impeller. If the
suction liquid level is below the centerline of the pump impeller, it is a static
suction lift.
Static Discharge Head. The static discharge head h is the difference in
d
elevation between in discharge liquid level and the centerline of the pump
impeller.
Static Head. Static H stat is the difference in elevation between the static
discharge and static suction liquid levels (h – h ).
d
s