pumps. Anderson (1994) and Wislicenus (1965) give details of construc-
tion and performance characteristics of pumps. For a detailed discussion
of rotodynamic pump design see Turton (2006).
The types of pumps and their applications are listed in Table 13.1 as
a guideline for their selection.
13.2.3 Specific speed Ns
Specific speed is the parameter which characterizes the rotodynamic
pumps more explicitly and is given by
NsNQ1/2/Hm3/4 (13.1)
whereQis the discharge (1 s^1 ),Hmthe total (manometric) head (m), and
Nthe rotational speed (rev min^1 ). The ranges of the specific speed for the
various types of pumps are shown in Table 13.2.
550 PUMPING STATIONS
Table 13.1 Types of pumps and their applications
Type Discharge Head Applications and remarks
Rotodynamic pump: To pump water and sewage; higher
radial-flow type Low High efficiencies in pumping clean water;
(30 m) sewage pumps are slow speed,
axial-flow type High Low unchokable pumps (capable of
(up to15 m) disintegrating solids);
mixed-flow type Medium Medium usually axial flow (propeller) type
(25–30 m) (Fig. 13.1(b))
Reciprocating pump Low Medium Very viscous fluid pumping; well and
borehole pumping; leakages unavoidable;
inefficient
Air-lift pump Low Low Groundwater recovery from wells with
large quantities of sand and silt;
inefficient
Jet pump Low Medium Combined with centrifugal pump;
borehole abstraction; inefficient
Screw pump High Low Archimedes screw principle; low speed;
to pump activated sludge or liquids
with flocs
Helical rotor pump Low Low Positive displacement pump with helical
rotor and stator elements; used for
sewage or liquids with suspended matter
pumping; borehole pump for water
supply
