Page 263 - Water Engineering Hydraulics, Distribution and Treatment

Chapter8
Pumping, Storage, and Dual Water Systems
valve is tripped by the rising water and admits compressed
8.1 PUMPS AND PUMPING STATIONS
air to the vessel.
Pumps and pumping stations (Figs. 8.1 and 8.2) serve the
Today most water pumping is done by either centrifu-
following purposes in water systems:
gal pumps or propeller pumps. These are usually driven by
electric motors, less often by steam turbines, internal com-
1. Lifting water from its source (surface or ground), bustion engines, or hydraulic turbines. How the water is
either immediately to the community through high- directed through the impeller determines the type of pump.
lift installations, or by low-lift systems to purification There are (1) radial flow in open- or closed-impeller pumps,
works with volute or turbine casings, and single or double suction
through the eye of the impeller; (2) axial flow in propeller
2. Boosting water from low-service to high-service
pumps; and (3) diagonal flow in mixed-flow, open-impeller
areas, to separate fire supplies, and to the upper floors
pumps. Propeller pumps are not centrifugal pumps. Both
of many-storied buildings
centrifugal pumps and propeller pumps can be referred to as
3. Transporting water through treatment works, back- rotodynamic pumps.
washing filters, draining component settling tanks, Single-stage pumps have but one impeller, and mul-
and other treatment units; withdrawing deposited tistage pumps have two or more, each feeding into the
solids; and supplying water (especially pressure next higher stage. Multistage turbine well pumps may have
water) to operating equipment their motors submerged, or they may be driven by a shaft
from the prime mover situated on the floor of the pumping
station.
In addition to centrifugal and propeller pumps, water
systems may include (a) displacement pumps, ranging in
size from hand-operated pitcher pumps to the huge pumping
engines of the last century built as steam-driven units; (b) 8.2 PUMP CHARACTERISTICS
rotary pumps equipped with two or more rotors (varying in
shape from meshing lobes to gears and often used as small A centrifugal pump is defined by its characteristic curve,
fire pumps); (c) hydraulic rams utilizing the impulse of large which relates the pump head (head added to the system) to
masses of low-pressure water to drive much smaller masses the flow rate. Pumping units are chosen in accordance with
of water (one-half to one-sixth of the driving water) through system heads and pump characteristics. As shown in Fig. 8.3,
the delivery pipe to higher elevations, in synchronization with the system head is the sum of the static and dynamic heads
the pressure waves and sequences induced by water hammer; against the pump. As such, it varies with required flows and
(d) jet pumps or jet ejectors, used in wells and dewatering with changes in storage and suction levels. When a distribu-
operations, introducing a high-speed jet of air through a noz- tion system lies between pump and distribution reservoir, the
zle into a constricted section of pipe; (e) air lifts in which system head also responds to fluctuations in demand. Pump
air bubbles, released from an upward-directed air pipe, lift characteristics depend on pump size, speed, and design. For
water from a well or sump through an eductor pipe; and (f) a given speed N in revolutions/min, they are determined by
displacement ejectors housed in a pressure vessel in which the relationships between the rate of discharge Q, usually
3
water (especially wastewater) accumulates and from which in gpm (or L/m or m /s) and the head H in ft (or m), the
it is displaced through an eductor pipe when a float-operated efficiency E in %, and the power input P in horsepower (or

Water Engineering: Hydraulics, Distribution and Treatment, First Edition. Nazih K. Shammas and Lawrence K. Wang.
© 2016 John Wiley & Sons, Inc. Published 2016 by John Wiley & Sons, Inc.

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