TOPIC 3:
PUMPS
INTRODUCTION
• A pump is a device used to moves and/or
pressurize fluids such as liquids.
• A pump moves fluid from lower pressure to
higher pressure and overcomes the difference
in pressure by adding energy to the system.
SELECTING A PUMP
a. Stability of the Head (H) vs Discharge (Q)
relationship
b. Operational flexibility
c. Future population increase
d. Deterioration of the delivery pipework with age
e. Uncertainty or errors in the original calculations.
ROTODYNAMIC PUMPS
Based on bladed impellers which rotate within the fluid to
impact a tangential acceleration to the fluid and consequent
increase in the energy of the fluid.
Type of rotodynamic pump
a) Centrifugal pump
b) Radial, Axial and Mixed Flow Devices
4
CENTRIFUGAL PUMPS
Definition:
Centrifugal
pumps
increase
momentum and pressure head by
means of rotating blades which
converts radial velocity into
pressure head.
Components
– Inlet duct
– Impeller
– Volute
– Discharge nozzle
Velocity head is imparted to the liquid by the vanes of
the impeller and is converted into pressure head
Variables that affect pump operation.
▪ Flow rate
▪ Impeller
▪ Size & diameter
▪ Process liquid characteristics
▪ Impeller speed
▪ Impeller vanes
Pressure (h)
a) Use head instead of pressure
b) Pressure will change with varying specific gravities of fluids
c) Head is a measure of the kinetic energy transferred to the
liquid from the pump-it is unaffected by specific gravity
d) Same head curve for all liquids
Flow rate (Q)
a) Flow rate determines the capacity of the pump.
b) Capacity: the flow rate with which liquid is moved or pushed
by the pump to the desired point in the process
POSITIVE DISPLACEMENT PUMPS
Cause a fluid to move by periodically trapping a fixed amount of
fluid and then forcing(displacing) that tapped volume into
discharge pipe.
Type of Positive Displacement Pumps
a)
Root type pumps
b) Reciprocating type pumps
POSITIVE DISPLACEMENT PUMPS
Typical Characteristics
a) Constant Flow at Various Pressures
b) Pulse Flow is possible
c) Most can pump solids suspended in liquids
d) Self-priming
TYPES OF POSITIVE DISPLACEMENT PUMPS
Rotary Pumps
a) Gear – Internal, External
b) Lobe
c) Vane
d) Screw
Reciprocating Pumps
a) Piston
b) Plunger
c) Diaphragm
PUMPING SYSTEM CHARACTERISTICS
destination
Head (H)
Static
head
a) Resistance of the system
b) Two types: static and friction
source
Static head (Hs)
a) Difference in height between Static
head
source and destination
b) Independent of flow
Flow
11
PUMPING SYSTEM CHARACTERISTICS
Friction head
a)
Resistance to flow in pipe and fittings
b) Depends on size, pipes, pipe fittings, flow rate,
nature of liquid
c)
Proportional to square of flow rate
d) Closed loop system
only has friction head
(no static head)
Friction
head
Flow
12
In most cases:
Total head = Static head (Hs) + friction head (hf)
System
curve
Friction
head
System
head
System
curve
System
head
Friction
head
Static head
Static head
Flow
Flow
13
Pumping System Characteristics
Pump performance curve
• Relationship between head and flow
a)
Head
Flow increase
b) System resistance increases
c)
Head increases
d) Flow decreases to zero
• Zero flow rate: risk of pump burnout
Flow
Performance curve for
centrifugal pump
14
PUMPING SYSTEM CHARACTERISTICS
Pump operating point
Duty point : rate of flow at certain head
Pump operating point : intersection of pump curve and system
curve
Pump performance
curve
Head
System
curve
Pump
operating
point
Design Point Curve
Static
head
Flow
15
PUMPING SYSTEM CHARACTERISTICS
Pump suction performance (NPSH)
Cavitation or vaporization: bubbles inside pump
If vapor bubbles collapse
a) Erosion of vane surfaces
b) Increased noise and vibration
c) Choking of impeller passages
Net Positive Suction Head
a) NPSH Available: how much pump suction exceeds liquid
vapor pressure
b) NPSH Required: pump suction needed to avoid
cavitation
16
ENERGY CONVERSION
Pump and Turbines
- Pump turn electrical or mechanical energy into
fluid energy
- Turbines turn fluid energy into electrical or
mechanical energy
- Energy per unit weight is head, H
H = z + v2 + P
2g ρg
- Power = rate of conversion of energy
- Power = ρgQH
- Efficiency, η = power out x 100%
power in
PUMP CHARACTERISTIC
Pump Performance Characteristics (Curves)
• Mathematical equations relating the variables H, Q, N, P and h are long
and complicated. It is more convenient to hold the information in the
form of graphs, using data obtained from performance tests.
• Pumps are usually tested at constant speed N, and the other variables
plotted against discharge Q. The tests are repeated for different speeds,
producing a family of characteristic curves.
CENTRIFUGAL PUMP CURVES
COMMON CAUSES OF CAVITATION
Situations:
a) Pumping liquid close to boiling point
b) Pumping liquid stored at a level below the pump
EFFECT OF CAVITATION
• Pump makes loud chattering noise
• Drop in pump efficiency
• Future failures due to metal erosion of
impeller (Long term)
• Future failures of seals on the shaft (Long
term)
CAVITATION
If the pump operates to the right of point A,
then the required suction head is greater than
the available suction head.
a)
This means that vapor bubbles will occur in
the suction pipe.
b)
As the vapor bubbles move through the
pump, the pressure will increase and the
bubble will collapse.
c)
This process is called Cavitation and can
cause severe damage to the pump.
d)
Operation to the left of point A means that
vapor bubbles will not form, and so
Cavitation will not be a problem.
PUMP
• NPSH – The amount by which pressure at the
suction point of pump, expressed as the head
of the liquid to be pump, must exceed the
vapor pressure of the liquid
• Cavitation – formation, growth and rapid
collapse of vapor bubble in flowing liquids.
PUMP PERFORMANCE
a) The performance of a pump is show by
its characteristic curve, where the flow
capacity (Q) is plotted against the
delivery pressure or developed head
(H).
b) Head is measured in meters.
FLOW = Q m3 /s
ASSIGNMENT 1
1. Describe the basic pump classification
2. Identify types of pump
a) Reciprocating pump
b) Centrifugal pump
3. Explain the concept of performance and characteristics of
centrifugal pump
a) Radial flow
b) Axial Flow
4. Explain the performance- degrading effect of a centrifugal
pump
a) Cavitation
b) Internal recirculation
ASSIGNMENT REPORT
• INDIVIDUAL
• ARIAL 12
• PDF FORMAT
• SOFTCOPY
• COVER PAGE
• TABLE OF CONTENT
• INTRODUCTION
• ANSWER Q1 – Q4
• CONCLUSION
• REFERENCE
STATIC AND DYNAMIC HEAD
a) The Static Head (H) is the
difference between Suction Head
(HS) and Delivered Head (HD).
b) As the Suction Head changes the
Static Head changes.
c) When the pump is operating the
liquid will be moving within the
pipe wok and so a loss due to
friction will occur.
d) Dynamic Head
H = H D − HS − H F
LOSSES DUE TO FRICTION
• A centrifugal pump incurs head losses due to
friction.
• The friction is caused by the fluid changing
direction when travelling through the pump
and by clearances within the pump .These
losses vary with both head and flow.
SYSTEM CHARACTERISTICS
H system = H static + HL
fLQ 2
H system = H static + ( h f = 3D 5 + hm)
f = friction factor
D = Diameter of pipe
Hf = head loss due to friction
Hm = minor head loss
HL = Hf + Hm
PUMPING SYSTEM CHARACTERISTICS
Pump operating point
Duty point : rate of flow at certain head
Pump operating point : intersection of pump curve and system
curve
Pump performance
curve
Head
System
curve
Static
head
Flow
Pump
operating
point
Design Point Curve
PUMPS IN SERIES
• Same discharge : Q
• Add the heads : H1 + H2
• Pump in series may be necessary to generate high
heads, or provide regular “boosts” along long
pipelines without large pressures at any particular
points
PUMP IN PARALLEL
Same head : H (H1 = H2)
Add the discharge : Q1 + Q2
Advantages of pumps in parallel are;
- High capacity :- permits a large total discharge
- Flexibility : pumps can be brought in and out of service if the
required discharge varies
EXERCISE 1
A centrifugal pump running has following characteristics:
Q (l/s)
0
50
100
150
200
250
300
350
H (m)
22.5
22
20.9
19
16.3
12.7
7.7
0
n (%)
25
38
60
75
80
78
65
44
H static – 12 meter
Pipe length – 80 m
Diameter of pipe 300 mm
fLQ 2
hf =
3D 5
Q (l/s)
0
50
100
150
200
250
300
350
H (m)
22.5
22
20.9
19
16.3
12.7
7.7
0
n (%)
25
38
60
75
80
78
65
44
a)
Plot the pump characteristic graph
b) Determine the value of Q, H and efficiency , n at duty point.
c) Determine the value of Q at optimum point.
d) Determine the output power at the duty point
e) Determine the discharge and head produced by connecting
pump
i. in series
ii. in parallel
Determine the power demand at the duty point in the case
parallel.
Hs = 12 + 109.74 Q2
P = ρgQH
fLQ 2
hf =
3D 5
Darcy Weisbach
Equation
Q (l/s)
0
50
100
150
200
250
300
350
Q
(m3/s)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
H (m)
22.5
22
20.9
19
16.3
12.7
7.7
0
n (%)
25
38
60
75
80
78
65
44
P
0
10.8
20.5
28
32
31.1
22.7
0
Hs
12
12.3
13.1
14.5
16.4
18.9
21.9
25.4
SERIES PUMP 2H vs Q
Q
(m3/s 0
)
2H 45
0.1
0.1
0.2
0.2
0.3
0.3
0.4
44
42
38
33
25
15
0
Series – H2 = 2H1 - 2H vs Q
PARALLEL H vs 2Q
H (m)
23
22
21
19
16
13
7.7
0
2Q
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Parallel – Q2 = 2Q1 - H vs 2Q
Q (l/s)
0
50
100
150
200
250
300
350
Q
(m3/s)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
H (m)
22.5
22
20.9
19
16.3
12.7
7.7
0
n (%)
25
38
60
75
80
78
65
44
P
0
10.8
20.5
28
32
31.1
22.7
0
Hs
12
12.3
13.1
14.5
16.4
18.9
21.9
25.4
2H
45
44
41.8
38
32.6
25.4
15.4
0
2Q
0
0.10
0.20
0.30
0.40
0.50
0.60
0.70
Parallel – Q2 = 2Q1 - H vs 2Q
Series – H2 = 2H1 - 2H vs Q
CHARACTERISTIC PUMP GRAPH
EXERCISE 2
A centrifugal pump produced the following
performance data on a test run
Flow, Q
(liter/sec)
75
150
200
250
300
350
Total Head,
H(m)
70
68
64
58
49
40
Input Power
(kW)
97
127
147
163
170
175
The pump required to deliver water from a sup to a reservoir
whose level is 60 m above that of the sump. Suction and
delivery pipes of 300 mm diameter will have a combined length
of 120m. Neglecting minor losses and assuming f = 0.006
a) plot graphs of pump head, system head and efficiency versus
flow on a same piece of graph paper
b) determine the discharge and head for the system at the
design point of the pump used in the system.
c) determine the discharge, head and efficiency of the pump
used at the duty point.
d) hence calculate the output power of the pump at the duty
point.
EXERCISE 3
A rotodynamic pump, having the characteristic tabulated below, delivers water
from a river at elevation 102 m to a reservoir with a water level of 135 m,
through a 350 mm diameter cast iron pipe. The frictional head loss in the
pipeline is given by hf = 550 Q2, where hf is the head loss in m and Q is the
discharge in m3/s. Minor head losses from valves and fittings amount to 50Q2 in
the same units.
Hsys = (135 – 102) + (550 + 50)Q2
= 33 + 600 Q2
Q (m3/s)
0
0.05
0.10
0.15
0.20
H(m)
60
58
52
41
25
 (%)
0
44
65
64
48
Hsys = 33 + 600Q2
Q (m3/s)
0
0.05
0.10
0.15
0.20
H(m)
60
58
52
41
25
Η (%)
0
44
65
64
48
a) Calculate the discharge and head in the pipeline (at duty
point) [Q = 0.137 m3/s, H = 44 m]
b) If the discharge is to be increased by the installation of a
second identical pump:
i. In parallel [ 0.185 m3/s, 53.5 m]
ii. In series [0.192 m3/s, 55.1 m]
c) Determine the power demand at the duty point in the case
of parallel operation [155 kW]
Q (m3/s)
0
0.05
0.10
0.15
0.20
H(m)
60
58
52
41
25
Η (%)
0
44
65
64
48
Q (m3/s)
0
0.05
0.10
0.15
0.20
H(m)
60
58
52
41
25
Η (%)
0
44
65
64
48