2. Pumps
Pumps convert mechanical energy to fluid energy
A pump usually refers to a machine used for incompressible fluids
(water, oil); fans, blowers
Types of pumps
Positive displacement
Centrifugal pump
Axial flow pump
Mixed flow pump
2
3. Pumps: Types
Positive Displacement Pump
These types of pumps displace fixed
volumes of fluid during each cycle or
revolution of the pump.
No longer used for distribution system
pumping in most water systems, but
portable units may be used for
dewatering excavations during
construction.
3
4. Pumps: Types
Centrifugal Pump
Frequently used in water
distribution systems.
Water enters the pump through
the eye of the spinning impeller
and goes outward from the
vanes to discharge pipe.
A centrifugal pump consists of: a
rotating element (impeller) and
housing which encloses the
impeller and seals the
pressurized liquid.
4
5. Pumps: Types
Axial Flow pumps
In axial-flow pumps, the flow
enters and leaves the pump
chamber along the axis of the
impeller, as shown in Figure
In mixed flow pumps,
outflows have both radial and
axial components.
5
6. Pumps: Types
The pumps illustrated in Figure are both single-stage pumps, which means
that they have only one impeller.
(a) Typical centrifugal pump installation. (b) Typical axial-flow pump installation.
6
7. Pumps: Types
In multistage pumps, two or more impellers are arranged in series in such a
way that the discharge from one impeller enters the eye of the next
impeller.These types of pumps are typically used when large pumping heads
are required.
10. Head Developed by Pump
Head developed by a pump. In this case ps/γ is negative.
++−
++=−= s
ss
d
dd
sd z
g
Vp
z
g
Vp
HHh
22
22
γγ
The net head h delivered by the pump to the fluid
10
11. Performance of Pump
Head and Capacity (Q)
BHP (Brake Horsepower) and Capacity
Efficiency and Capacity
NPSH and Capacity
11
13. Pump Curve vs System Curve
13
With increasing discharge (Q) head losses (hL) in pipeline increase
and at the same time head provided (h) by pump reduce.
16. Specific Speed
For pumps, the commonly used definition of specific speed (also called
shape number), ns , is given by
where any consistent set of units can be used. In SI units, w is in rpm, Q in
m3/s, g in m/s2, and hp in meters.
It is common practice in the United States to define the specific speed,
Ns, as
16
18. Problem:
It is desired to deliver 100L/s at a head of 270m with a single stage pump.
(a).What would be the minimum rotative speed that could be used.
Assuming that the minimum practical specific speed, Ns, is 10.
(b). For the conditions of (a) how many stages must the pump (Ns=10)
have if a rotative speed of 600 rpm is to be used.
( )
( )
rpm
Q
hN
h
Q
N
ps
p
s
2106
1000/100
27010
2/1
4/3
2/1
4/3
4/3
2/1
==
=⇒=
ω
ω
ω
( )
stagepermh
N
Q
h
p
s
p
6.50
19
10
1.0600
2/12/1
4/3
=
===
ω
Total Reqd. Stages=270/50.6=5.34
6 stage are required
a.
b.
18
19. Problem:
Determine the specific speed of a pump that is to deliver 125L/s against a
head of 45m with a rotative speed of 600rpm.
( )
( )
2.12
45
1000/125600
4/3
2/1
4/3
2/1
==⇒= ω
ω
p
s
h
Q
N
19
20. Total Dynamic Head
To determine the size of the pump, one must know the total dynamic head
that the pump is expected to provide.
Total dynamic head (TDH) consists of
The difference between the center line of the pump and the height to
which water must be raised.
The difference between the suction pool elevation and centerline of the
pump
Frictional losses in the pump and fitting
Velocity head
Mathematically, it can be written as;
TDH=Hs + HL + Hv
Hs= Total static head (difference between elevations of pumping source and point of delivery
HL = Friction losses in pipes and fittings
Hv=Velocity head due to pumping
20
21. Total Dynamic Head (Head Added by Pump)
If a pump has been selected, Bernoulli’s equation can be rearranged to solve
for the head added by a pump
Where,
ha=head added by pump (TDH)
hf= head loss in attached pipe and fittings
P=Atmospheric pressure
V=velocity
Z=elevation
( ) fa hZZ
VVPP
h +−+
−
+
−
= 12
2
1
2
212
γγ
21
24. Head Added by Pump
A pump is being used to deliver 35gpm of
hot water from a tank through 50feet of 1-
inch diameter smooth pipe, exiting
through a ½ inch nozzle 10 feet above the
level of tank.The head loss due to friction
in the pipe is 26.7 feet.The specific weight
of water is 60.6 lb/ft3. Determine the head
added by pump.
24
50’10’
37. Cavitation
37
For any operating pump, a
cavitation parameter, σ, is defined
by the relation
where hp is the head added by the
pump.
For all pumps, there is a critical value
of the cavitation parameter, σc below
which cavitation in the pump can be
expected to occur.
This critical value of the cavitation
parameter is usually provided by the
pump manufacturer and generally
places a limit on the operating range
of the pump
Values of σc as a function of
specific speed
38. Net Positive Suction Head (NPSH)
• The absolute dynamic head at the pump inlet (suction) in
excess of the vapor pressure
51. Pumps in Series and Parallel
Pumps can be arranged in serial or parallel to provide an
additional head or flow rate capacity.
52. Pumps in Series
52
When two (or more) pumps are arranged in serial their
resulting pump performance curve is obtained by adding
their heads at the same flow rate as indicated in the figure below.
53. Pumps in Parallel
When two or more pumps are arranged in parallel their
resulting performance curve is obtained by adding their
flowrates at the same head as indicated in the figure below.
53
