Volume 8 – Mechanical and Electrical Services - Malaysia Geoportal

Chapter 1 PUMPING INSTALLATION
1.2 PUMP PERFORMANCE AND CHARACTERISTICS
Pump overall performance is always expressed by characteristic curves of the total head, horsepower
and efficiency plotted against capacity at constant speed. Fig 1.4 shows the typical pump
characteristics of various types of pumps with respect to the pump specific speed (Ns). Table below
shows types of pumps for various specific speeds.
Specific speed
range (Ns) – metric
unit
Head (m)
Table 1.1 Pump Characteristics for Various Types Of Pump
Pump Type
Radial / Francis Mixed-flow Axial- flow
Radial : 10 – 60
Francis: 30 - 90 90 - 160 > 160
High head,
18 – 300
Moderate head,
9 - 18
H – Q curve Flat Moderate steep Steep
Efficiency High High High
Power curve:
(i) Unstable and
overloading
(ii) Stable and
non-overloading
Yes at lower Ns.
Yes, at higher Ns.
Yes, power curve varies
little with working
range.
-
Low head,
3 – 9
Yes, power curve
falls rapidly with
flow.
Suction lift High Moderate Low
General
Heavy and higher Moderate
Smaller and
equipment cost
cheaper
-
1-6 March 2009