1. ENG421 (3c) – Pipes, Valves, Pumps
Pump characteristics
Distribution Boosting
Pumping Installation

2. Pump Characteristics (1 of 12)
characteristic differences between centrifugal, mixed-flow and air-lift pumps
depends on :
- speed
- output
- head conditions
for all three pumps, flow increases as head decreases

3. Pump Characteristics (2 of 12)
Specific Speed
defined as speed of ideal pump geometrically similar to actual pump
enables comparison of pumps by reference to specific speed
helps to specify pumps that are more efficient
Ns is specific speed (dimensionless)
n is pump rotational speed (revolutions per second)
Q is flowrate (m³/s) at the point of best efficiency
H is total head (m) per stage at the point of best efficiency
g is acceleration due to gravity (m/s²)

4. Pump Characteristics (3 of 12)
Specific Speed (cont)

5. Pump Characteristics (4 of 12)
Characteristic Curves
for roto-dynamic pump :
quantity of fluid pumped varies directly as speed of rotation
head varies as square of the speed
power consumption varies as cube of the speed
design point - pump operates at maximum efficiency

6. Pump Characteristics (5 of 12)
Characteristic Curves (cont)

7. Pump Characteristics (6 of 12)
Power Input
required by pump

8. Pump Characteristics (7 of 12)
Selection of Pumps
choice of pump depends on :
type of use
flow velocity
head requirements
specify complete range of duties
not just “normal” operating conditions
supplier/manufacturer will be able to advise
for full output of large pumping station
single pump is rarely used
to ensure continuity of supply use standby pump(s)
two pumps – each 100% of duty
three pumps – each 50% of duty

9. Pump Characteristics (8 of 12)
Selection of Pumps (cont)
Horizontal Centrifugal Pump
suitable for all water works duties
except - large volume against low head
- pumping from wells and boreholes
advantages :
cheap
great variety of designs (meet wide range of pumping conditions)
for high-lift pumping : fixed speed, multi-staged horizontal centrifugal pump
is most economical
Submersible Pump
suitable for pumping from wells and boreholes
including from well to high level tank
specifically preferred in wet conditions

10. Pump Characteristics (9 of 12)
Prime Movers
pumps are driven either by
- direct-coupled electric motors
- internal combustion engines
petrol, diesel, oil, gas
good for remote locations
infrequent duty demand

11. Pump Characteristics (10 of 12)
Prime Movers (cont)
Electric Motors
generally more economical, both capital and operating costs
unless - power is not available at the site
- pumping only required at infrequent intervals
e.g. storm, sewage, and surface water pumping
flood control works
preferred due to :
very good for unattended operation (un-manned)
very suitable for automatic control
reliability
efficiency
quietness in operation
have diesel back-up for power failure

12. Pump Characteristics (11 of 12)
Automatic Control of Pumping
electronic, automated control
eliminates need for 24 hour per day manned attendance
additional cost for control equipment
repaid many times by savings in labour costs
usually only for grid-fed electric motors (not diesel driven pumps)
programmable logic controllers (PLC)
start/stop conditions (level, time, pressure)
remote control
remote monitoring

13. Pump Characteristics (12 of 12)
Automatic Control of Pumping (cont)
protection for various devices in pumping systems

14. Distribution Boosting (1 of 5)
any pumping arrangement that increases the pressure or flow of water
though an existing pipeline system
Addition of fixed extra flow or pressure
- for extra flow
install additional pump in parallel to existing pump
add flows for a given head
consider extra flow increases frictional losses
causes drop in delivery head

15. Distribution Boosting (2 of 5)
Addition of fixed extra flow or pressure (cont)
- for extra pressure
install additional pump in series to existing pump
add heads for a given flow
consider extra pressure increases internal forces in pipe
causes failure of pipe

16. Distribution Boosting (3 of 5)
Addition of fixed extra flow or pressure (cont)
effect of boosting flow in a rising main to a reservoir

17. Distribution Boosting (4 of 5)
Maintenance of a given pressure
common use of booster pump is to increase pressure of water over
distribution system
especially at times of high draw-off
during low demand (e.g. night time flow) pressure at end of distribution
mains may satisfy pressure requirements
for high demand times increase pressure by :
- laying additional distribution mains (expensive)
- booster pump at times of high flow

18. Distribution Boosting (5 of 5)
Maintenance of a given pressure (cont)
effect of boosting pressure of water directly into distribution systems

19. Pumping Installation (1 of 2)
Several possible layouts for a pumping station
site may be set by technical requirements
consider :
- amenity of locality
- accessibility for construction
- accessibility for maintenance
- suction and delivery pipework to each pump
control valves to be installed
- provision of one or more reserve (standby) pumps
facilitates maintenance on other pumps
- electrical switchgear, instrument paneling, pressure gauges,
flow measurement devices
- water hammer protection

20. Pumping Installation (2 of 2)

21. References
Nemerow, N.L. et al, 2009, Environ Eng : Water, Wastewater, Soil and Ground, 6th ed., John Wiley and Sons, New York (TD430 .E ), pages
Twort, A.C. et al, 2000, Water Supply, 5th ed., Arnold, London (TD345T ), pages
Viessman, W. et al, 2009, Water Supply and Pollution Control, 8th ed., Pearson, Upper Saddle River, pages 179 – 189