Pumps

PUMPS
Machine that provides energy to a fluid in a fluid
system.
Converts the mechanical energy supplied to it externally
to hydraulic energy and transfers it to the liquid flowing
through a pipe
Flow is normally from high pressure to low pressure
Nazmy Markos, M.Sc., P.Eng. FEC
NAZMY MARKOS 1

PUMPS
On the basis of mode of action of conversion of
mechanical energy to hydraulic energy, pumps are
classified as
 Rotodynamic pumps
 Positive displacement pumps
In rotodynamic pumps, increase in energy level is due to
combination of centrifugal energy, pressure energy and
kinetic energy
In displacement pumps, liquid is sucked and then
displaced due to the thrust exerted on it by a moving
member that results in the lifting of liquid to a desired
height.
NAZMY MARKOS 2

CENTRIFUGAL PUMPS
Introduction:
Centrifugal pumps are the rotodynamic machines that
convert mechanical energy of shaft into kinetic and
pressure energy of water which may be used to raise
the level of water. The wheel in which this conversion is to
realized is known as a impeller. A centrifugal pump is
named so, because the energy added by the impeller to
the fluid is largely due to centrifugal effects.
NAZMY MARKOS 5

CLASSIFICATION OF CENTRIFUGAL
PUMPS
Centrifugal pumps may be classified according to,
1.Working head
2.Specific speed
3.Type of casing
4.Direction of flow of water
5.Number of entrances to the impeller
6.Disposition of shaft
7.Number of stage
NAZMY MARKOS 6

CENTRIFUGAL PUMP
Electric
Motor
NAZMY MARKOS 7

CENTRIFUGAL PUMP
Converts kinetic energy to
pressure energy
NAZMY MARKOS 8

PUMPS
1. Working Head
Centrifugal pumps may be classified in to low, medium
and high-head pumps.
Low-Head Centrifugal Pumps
These are usually single-stage-centrifugal pumps and
work below 15m head.
Medium-Head Centrifugal Pumps
When the head lies between 15 and 45 m, the pumps
are called medium-head-centrifugal pumps.
NAZMY MARKOS 10

CLASSIFICATION OF CENTRIFUGAL PUMPS
High-Head Centrifugal Pumps
When the head exceeds 45m, the pumps are known
as high-head-centrifugal pumps. Usually these are
multistage pumps, and are provided with guide vanes.
These pumps may have horizontal or vertical shafts.
Vertical shafts are useful in deep wells.
NAZMY MARKOS 11

CENTRIFUGAL PUMP
A centrifugal pump may be defined as a pump that uses centrifugal force
to develop velocity in the liquid being handled. The velocity is then
converted to pressure when the liquid velocity decreases. As kinetic energy
is decreased, pressure is increased
NAZMY MARKOS 12

CENTRIFUGAL PUMP
OPERATING PRINCIPLE
The working principle of a centrifugal
pump is shown diagrammatically in Figure
1. Rotation of the impeller causes any
liquid contained in it to flow towards the
periphery because of the centrifugal
force generated. The center or eye of the
impeller is thus evacuated and liquid from
the suction line then flows in to fill the
void.
NAZMY MARKOS 13

Diameter of
the Impeller
Thickness
of the impeller
CENTRIFUGAL IMPELLERS
Thicker the Impeller- More Water
Larger the DIAMETER - More Pressure
Increase the Speed - More Water and Pressure
Impeller
Vanes
“Eye of the
Impeller”
Water
Entrance
NAZMY MARKOS 14

TWO IMPELLERS IN SERIES
Twice the pressure
Same amount of water
Direction of Flow
NAZMY MARKOS 15

MULTIPLE IMPELLERS IN SERIES
Placing impellers in series increases the amount of head
produced
The head produced = # of impellers x head of one impeller
Direction of Flow Direction of Flow
NAZMY MARKOS 16

PUMP PERFORMANCE CURVE
A mapping or graphing of the pump's ability to produce head and
flow
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STEP #1, HORIZONTAL AXIS
The pump's flow rate is plotted on the horizontal axis ( X
axis)
Usually expressed in Gallons per Minute
Pump Flow Rate
NAZMY MARKOS 18

STEP #2, VERTICAL AXIS
The head the pump produces is plotted on
the vertical axis (Y axis)
Usually express in Feet of Water
Pump Flow Rate
Head
NAZMY MARKOS 19

STEP #3, MAPPING THE FLOW AND THE HEAD
Most pump performance
curves slope from left to
right
Pump Flow Rate
Performance Curve
Head
NAZMY MARKOS 20

IMPORTANT POINTS
Shut-off Head is the maximum pressure or
head the pump can produce
No flow is produced
Pump Flow Rate
Head
Shut-off Head
NAZMY MARKOS 21

IMPORTANT POINTS
Maximum Flow is the
largest flow the pump can
produce
No Head is produced
Pump Flow Rate
Head
Maximum Flow
NAZMY MARKOS 22

DIFFERENT TYPES OF PUMP HEAD
Total Static Head - Total head when the pump is not running
Total Dynamic Head (Total System Head) - Total head when the pump is
running
Static Suction Head - Head on the suction side, with pump off, if the head
is higher than the pump impeller
Static Suction Lift - Head on the suction side, with pump off, if the head is
lower than the pump impeller
Static Discharge Head - Head on discharge side of pump with the pump
off
Dynamic Suction Head/Lift - Head on suction side of pump with pump on
Dynamic Discharge Head - Head on discharge side of pump with pump
on
NAZMY MARKOS 23

PUMP HEAD
The head of a pump can be expressed in metric units
as:
head = (p2 - p1)/(ρg) + (v2
2- v1
2)/(2g) + (z2-z1)
where
h = total head developed (m)
p2 = pressure at outlet (N/m2)
p1 = pressure at inlet (N/m2)
ρ = density of liquid (kg/m3)
g = acceleration of gravity (9.81) m/s2
v2 = velocity at the outlet (m/s)
NAZMY MARKOS 24

PUMP EFFICIENCY
Centrifugal Pump
NAZMY MARKOS 25

PUMP PERFORMANCE CURVES
Resistance
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PUMP DESIGN SCALING
Pump Flow rate
 Q2 = Q1 x [(D2xN2)/(D1xN1)]
Pump Head
 H2 = H1 x [(D2xN2)/(D1xN1)]2
Pump Brake Horse Power
 BHP2 = BHP1 x [(D2xN2)/(D1xN1)]3
 D = Impeller Diameter
 N = specific speed
NAZMY MARKOS 27

NET POSITIVE SUCTION HEAD-NPSH
Pumps can not pump vapors!
The satisfactory operation of a pump requires that vaporization of the
liquid being pumped does not occur at any condition of operation.
NAZMY MARKOS 28

NET POSITIVE SUCTION HEAD REQUIRED,
NPSHR
As the liquid passes from the pump suction to the eye of the impeller, the velocity increases
and the pressure decreases. There are also pressure losses due to shock and turbulence as
the liquid strikes the impeller. The centrifugal force of the impeller vanes further increases
the velocity and decreases the pressure of the liquid. The NPSH required is the positive
head (absolute pressure) required at the pump suction to overcome these pressure drops in
the pump and maintain the liquid above its vapor pressure.
NAZMY MARKOS 29

NET POSITIVE SUCTION HEAD AVAILABLE, NPSHA
Net Positive Suction Head Available is a function of the system in which the
pump operates. It is the excess pressure of the liquid in feet absolute over its vapor
pressure as it arrives at the pump suction, to be sure that the pump selected does not
cavitate.
Head to Feed Pump Subcooling before Pump
To overcome suction head
Head
Designed into
Installation
HX
Cool a few Degrees
To overcome suction head
NAZMY MARKOS 30

CENTRIFUGAL PUMP
Centrifugal pumps can be subdivided into the following types:
volute,
diffuser,
axial flow,
mixed flow
regenerative.
NAZMY MARKOS 32

VOLUTE CENTRIFUGAL PUMP
Basically, the volute centrifugal pump
consists of an impeller, made up of a
number of vanes, which rotates in a
volute stationary casing. The term
"volute" refers to the gradually
increasing cross-sectional area of the
spiral casing.
NAZMY MARKOS 33

VOLUTE CENTRIFUGAL PUMP
The liquid being pumped is drawn
into the center or eye of the
impeller. It is picked up by the
vanes, accelerated to a high
velocity and discharged into the
casing by centrifugal force. As the
liquid travels through the volute
casing to the discharge, its velocity
energy is converted into pressure
energy. Since the liquid between
the vanes is forced outward, a low
pressure area is created in the eye
and more liquid is drawn in through
the suction inlet. As a result, the flow
of liquid through the pump is
constant
NAZMY MARKOS 34

DIFFUSER PUMP
In the diffuser centrifugal pump,
the high velocity liquid leaving the
impeller passes between a number
of vanes in a stationary diffuser
ring. These vanes are shaped in
such a way that the channels
between them gradually increase
in area. As the liquid passes
through these channels, its velocity
energy is converted into pressure
energy. The liquid is then
discharged either into a volute
casing or into a concentric casing
where farther velocity to pressure
conversion takes place.
NAZMY MARKOS 35

DIFFUSER PUMP
As these diffuser vanes are spaced
uniformly around the impeller
circumference there is no radial
imbalance developed. In addition,
in the diffuser pump the velocity
energy of the liquid is more
completely converted into pressure
energy than it is in the volute pump.
As a result, the diffuser pump is
commonly used for high capacity,
high pressure service.
NAZMY MARKOS 36

AXIAL FLOW PUMP
Axial flow pumps, also referred to as
propeller pumps, use impellers with
blades similar to those of an aircraft
propeller. The pump head is developed
by the propelling or lifting action of the
blades on the liquid.
The arrangement of the pump is usually
vertical as in Figure but horizontal and
inclined shaft arrangements are also
available. For the smaller pumps, fixed
blade type impellers are used. Larger
pumps may use impellers with
adjustable or variable-pitch blades
which can be used to maintain
efficiency at loads that differ from the
design load.
NAZMY MARKOS 37

IMPELLER TYPES
Impellers vary considerably in design. They can be classified
according to specific speed, the way the liquid is drawn into
the eye, vane design and pump application
NAZMY MARKOS 38

IMPELLER TYPES
The open impeller, A, has vanes attached to a central hub with a relatively small
shroud on one side. It is of end suction or single-inlet design, thus the water enters the
eye from one side only. B shows a semi closed single-inlet impeller. A full shroud
closes off one side. An enclosed, single-inlet impeller is shown in C. The liquid
passages between the vanes are closed off by the shrouds on both sides. Impeller D
is also enclosed but it has a double-inlet, thus water enters the eye from both sides.
Design E is used in paper-stock pumps handling liquids containing solids. F is a
propeller type impeller while impeller G is used in mixed-flow pumps.
NAZMY MARKOS 39

MULTISTAGING
Pumps may be either single or
multistage design. In-general,
single stage pumps are used for
heads of 120 m or less while the
multistage design is usually
necessary for heads above 120 m.
To obtain these higher heads,
centrifugal pumps are equipped
with two or more impellers
operating in series. That is, the
discharge of one impeller is
connected to the suction of the next
impeller. These pumps are known
as multistage pumps.
NAZMY MARKOS 40

AXIAL FLOW PUMP
The advantages of axial flow
pumps are their compact size and
the ability to operate at high
speeds, while their disadvantages
include low suction lift capacity and
relatively low discharge bead
capability. They are used mainly
for low head, high capacity
applications and are available in
the singlestage design or the
multistage
NAZMY MARKOS 41

MIXED FLOW PUMPS
Mixed flow pumps combine some of
the characteristics of the volute and
diffuser pumps together with some
axial flow pump features. The head
developed by this pump is
produced partly by centrifugal
force and partly by the lift of the
impeller vanes on the liquid.
The mixed flow pump shown in
Figure has a single-inlet impeller.
The flow enters the pump in an
axial direction and leaves the
pump in a direction somewhere
between axial and radial.
NAZMY MARKOS 42

MIXED FLOW PUMPS
The mixed flow pump, combines
some of the characteristics of the
radial flow and axial flow pumps. It
develops its discharge head by
using both centrifugal force and lift
of the vanes on the liquid. The
pump is built for vertical and
horizontal applications and it is
commonly used for low head, high
capacity operation.
NAZMY MARKOS 43

REGENERATIVE OR TURBINE PUMP
The regenerative pump or
turbine regenerative pump
as it is also called, features
an impeller with a double
row of vanes cut in the rim,
as illustrated in Figure 22.
Both the suction and the
discharge connections are
located in the casing at the
periphery of the impeller.
The liquid circulates almost
360 degrees before being
discharged
NAZMY MARKOS 44

NPSH
The NPSH required by a pump is the head of the liquid pumped,
measured at the suction nozzle of the pump, necessary to overcome all
energy requirements at the inlet of the pump (these included friction
losses, acceleration, heating effect of internally circulated liquid etc.)
and thereby avoid any vaporization of liquid in the pump suction. The
NPSH required is thus the head of the liquid required at the pump
suction nozzle above the vapour pressure of the liquid at that point.
for centrifugal pump The NPSH required is expressed in terms of
head of liquid pumped, and not pressure while for positive
displacement pump NPSH are not always expressed in terms of head
of liquid. In some cases-as in the case of Reciprocation Pumps- NPSH
is expressed as a pressure increment above the vapour pressure of
the liquid
NAZMY MARKOS 45

NPSH
NPSHA (Available) = Terminal Pressure in the vessel (in gauge)
(+) Static Head of fluid above pump centre line .
(+) Atmospheric Pressure
(-) Vapour Pressure of liquid at pumping temperature
(-) Friction loss in suction piping up to pump centre line consisting of the
following
NPSHR (required):
The net positive suction head required is a function of the pump
design at the operating point on the pump performance curve
▪ At any fixed speed, the NPSH required by a centrifugal pump will
increase with increase in flow from rated flow. At substantially
increased flow from design flow the increase in NPSHR is very rapid
NAZMY MARKOS 46

ADVANTAGES AND DISADVANTAGES OF
CENTRIFUGAL PUMPS
The advantages of centrifugal pumps include simplicity, compactness, weight
saving, and adaptability to high-speed prime movers.
One disadvantage of centrifugal pumps is their relatively poor suction power.
When the pump end is dry, the rotation of the impeller, even at high speeds, is simply
not sufficient to lift liquid into the pump; therefore, the pump must be primed before
pumping can begin. For this reason, the suction lines and inlets of most centrifugal
pumps are placed below the source level of the liquid pumped. The pump can
then be primed by merely opening the suction stop valve and allowing the force
of gravity to fill the pump with liquid. The static pressure of the liquid above the
pump also adds to the suction pressure developed by
the pump while it is in operation. Another disadvantage of centrifugal pumps is
that they develop CAVITATION. Cavitation occurs when the velocity
NAZMY MARKOS 47

CAVITATION
Cavitation is defined as phenomenon of formation of vapour bubbles
of a flowing liquid in a region where the pressure of the liquid falls
below its vapour pressure and collapsing of these vapour bubbles in a
region of higher pressure. When the vapour bubbles collapse and
very high pressure is created, the metallic surface above which the
liquid is flowing is subjected to these high pressures which cause pitting
action on the surface, thus cavities are formed on metallic surface and
also considerable nose and vibration created.
formation of vapour bubbles of flowing liquid takes place only
whenever the pressure in any region falls bellow vapour pressure, at
this time liquid starts boiling and vapour bubbles forms, these bubbles
carried along with the flowing liquid to the higher pressure zone
where this bubbles condense and bubbles collapse due to sudden
collapsing og the bubbles on metallic surface high pressure is
produced and surface subjected to high local stress.
NAZMY MARKOS 48

CAVITATION
Precaution against cavitation
➢The pressure of the flowing liquid in any part of the hydraulic system
should not be allowed to fall below vapour pressure (
NPSHA>NPSHR).
➢The special material or coating such as aluminum bronze and
stainless steel should be used.
NAZMY MARKOS 49

PUMPS
2. Specified Speed
Specific speed of a pump is defined as the speed of
a geometrically similar pump which delivers unit
discharge under unit head.
Ns = N√ Q / H3/4 --------------------------(10.4)
NAZMY MARKOS 50

PUMPS
2. Specified Speed
Following table gives the values of specific speed of
different types of pumps:
NAZMY MARKOS 51

PUMPS
3. Types of Casing
Pumps can be divided into following type according
to their casing:
a) Volute-Chamber Pump
b) Vortex-chamber Pump
c) Diffuser Pump
NAZMY MARKOS 52

PUMPS
3. Types of Casing
Such type of casing is of spiral form, and has a
sectional area, which increase uniform ally from the
tongue to the delivery pipe as shown in fig.10.1 more
area is provided to accommodate increased quantity
of water as the water moves towards the delivery
pipe.
NAZMY MARKOS 53

PUMPS
3. Types of Casing
NAZMY MARKOS 54

PUMPS
3. Types of Casing
In a vortex chamber, a uniformly increasing area is
provided between the impeller outer periphery and
the volute casing as shown in fig. 10.2 water, on
leaving the impeller becomes free to adopt its path.
NAZMY MARKOS 55

PUMPS
3. Types of Casing
NAZMY MARKOS 56

PUMPS
3. Types of Casing
c) Diffuser Pump
In a diffuser Pump, the guide vanes are arranged at
the outlet of the impeller vanes. Water enters the
guide without shock. As the guide vanes are of
enlarging cros-sectional area, the velocity of water
decreased and pressure increases Since the vanes
provide better guidance to flow, eddy losses are
reduced which increases the efficiency.
NAZMY MARKOS 57

PUMPS
3. Types of Casing
c) Diffuser Pump
NAZMY MARKOS 58

PUMPS
4. Direction of Flow of Water
Pumps can also have flow as under:
a) Radial Flow
b) Mixed Flow
c) Axial Flow
NAZMY MARKOS 59

PUMPS
a) Radial Flow
Radial flow is one in which the flow in the impeller is
completely in a radial direction. This is used when the
requirements are high and low discharge.
NAZMY MARKOS 60

PUMPS
b) Mixed Flow
In a mixed-flow, by changing the direction of flow
from pure radial to a combination of a radial and
axial, area of flow is increased. Thus mixed-flow
pumps are used where medium discharge is needed
to raise the water to medium heads. These are mostly
used for irrigation purposes.
NAZMY MARKOS 61

PUMPS
c) Axial Flow
These pumps find their use where high discharge at
low heads is required, as in irrigation.
NAZMY MARKOS 62

PUMPS
NAZMY MARKOS 63

PUMPS
5. Number of Entrances to the Impeller
Pumps can have either single or double entrance
according to the discharge needed:
a) Single – Suction Pump
b) Double – Suction Pump
NAZMY MARKOS 64

PUMPS
a) Single – Suction Pump
Pumps which have suction pipe only on one side of the
impeller are called single-suction pumps
NAZMY MARKOS 65

PUMPS
b) Double – Suction Pump
In double suction pumps, the suction is made from both
sides of the impeller (Fig. 10.5b). This increases the
discharge considerably.
NAZMY MARKOS 66

PUMPS
NAZMY MARKOS 67

PUMPS
6. Disposition of Shaft
Usually, the centrifugal pumps are used with
horizontal shafts. Vertical shafts are used where there
is space limitation i.e. in deep wells, mines etc.
NAZMY MARKOS 68

PUMPS
7. Number of Stages
A centrifugal pump can have a single stage with one
impeller keyed to the shaft or it can be a multi-stage
pumps. A multistage pump has a number of impellers
mounted on the same shaft and enclosed in the same
casing.
NAZMY MARKOS 69

EXAMPLE NO.1 A DOUBLE-SUCTION CENTRIFUGAL PUMP DELIVERS 2000 LITRES OF
WATER PER SECOND AGAINST A HEAD OF 25 M WHILE RUNNING AT 725 RMP. WHAT TYPE
OF IMPELLER SHOULD BE USED FOR THIS PUMP?
Sol. Considering only one half of the impeller,
H= 25 m
Q = 2000/2=1000 lit/s = 1 m3/s
N= 725rmp
Ns = N√ Q / H3/4
= 725√1/ (25)3/4
= 64.8
Thus a high-speed radial impeller should be used.
NAZMY MARKOS 70

EXAMPLE NO.2 A SIX-STAGE CENTRIFUGAL PUMPS DELIVERS 0.1 M3/S AGAINST A TOTAL
HEAD OF 480 M. WHAT IS ITS SPECIFIC SPEED IF IT ROUTES AT 1450 RPM ? WHAT TYPE
OF IMPELLER WOULD YOU RECOMMENDED FOR THE PUMP?
Sol.
Q = 0.1 m3/s
N= 1450 rmp
Head developed per impeller,
H = 480/6 = 80 m
Ns = N√ Q / H3/4
= 1450√0.1/ (80)3/4
= 17.14
For this specific speed, low-speed-radial impeller is suitable.
.
NAZMY MARKOS 71

COMPONENTS OF CENTRIFUGAL PUMPS
The Centrifugal pump has the following main components:
NAZMY MARKOS 72

Impeller
A rotating wheel fitted with a series of backward curved vanes or
blades mounted on a shaft connected to the shaft of an electric
motor. Due to rotation of impeller centrifugal force is produced on
the liquid, which produces kinetic energy in the liquid. Water
enters at the centre of the impeller and moves radially outward
and then leaves from outer periphery of the impeller with a very
high kinetic energy.
NAZMY MARKOS 73

Casing
It is an airtight chamber, which accommodates the rotating
impeller. The area of flow of the casing gradually increases in the
direction of flow of water to convert kinematic energy into
pressure energy.
NAZMY MARKOS 74

Suction pipe
It is the pipe through which water is lifted from the sump to the
pump level. Thus the pipe has its lower end dipped in the sump
water and the upper end is connected to the eye or the inlet of
the pump. At the lower end, a strainer and a foot-valve are also
fitted.
i. Strainer
It is a screen provided at the foot of the suction pipe, it would
not allow entrance of the solid matters into the suction pipe which
otherwise may damage the pump.
NAZMY MARKOS 75

Suction pipe
ii. Foot valve
It is a one direction valve provided at the foot of the suction
pipe. It permits flow only in one direction i.e. towards the pump.
Foot valve facilitates to hold the primed water in the suction pipe
and casing before starting the pump. Priming is the process of
filling of water in centrifugal pump from foot valve to delivery
valve including casing before starting the pump.
NAZMY MARKOS 76

Delivery pipe
Delivery pipe is used for delivery of liquid. One end
connected to the outlet of the pump while the other delivers the
water at the required height to the delivery tank. It consists of
following components:
i. Delivery gauge
This gauge connected on the delivery side of the pump to
measure the pressure on the delivery side.
ii. Delivery Valve
It is a gate valve on the delivery side of the pump to control
the discharge
NAZMY MARKOS 77

Shaft
It is a rotating rod supported by the bearings. It transmits
mechanical energy from the motor to the impeller.
Air Relieve Valve
These are the valves used to remove air from casing while
priming.
NAZMY MARKOS 78

WORKING OF CENTRIFUGAL PUMP
Works on the principle that when a certain mass of fluid is
rotated by an external source, it is thrown away from the
central axis of rotation and a centrifugal head is
impressed which enables it to rise to a higher level.
In order to start a pump, it has to be filled with water so
that the centrifugal head developed is sufficient to lift the
water from the sump. The process is called priming.
Pump is started by electric motor to rotate the impeller.
Rotation of impeller in casing full of water produces
forced vortex which creates a centrifugal head on the
liquid.
NAZMY MARKOS 79

WORKING OF CENTRIFUGAL PUMP
The delivery valve is opened as the centrifugal head is impressed.
This results in the flow of liquid in an outward radial direction with
high velocity and pressure enabling the liquid to enter the
delivery pipe.
Partial vacuum is created at the centre of the impeller which
makes the sump water at atmospheric pressure to rush through the
pipe.
Delivery of water from sump to delivery pipe continues so long as
the pump is on.
NAZMY MARKOS 80

HEADS OF A PUMP
1. Static Head
It is the vertical distance between water levels in the sump and
the reservoir.
Let Hst = Static head on the pump
hs = Height of the centre line of pump above the sump level
(Suction head)
hd = Height of the liquid level in the tank above the centre line
of pump (Delivery head)
Then, Hst = hs + hd
NAZMY MARKOS 81

HEADS OF A PUMP
2. Total Head
It is the total head which has to be developed by a pump to
deliver the water form the sump into the tank. Apart from
producing the static head, a pump has also to overcome the
losses in pipes and fittings and loss due to kinetic energy at the
delivery outlet.
Let H = Total head
hfs = Losses in suction pip
hfd = Losses in delivery pipe
hf = Total friction loss in pipe = hfs + hfd
Vd = Velocity of liquid in delivery pipe.
Then H = hs+ hd + hfs + hfd + Vd2/(2g)
Losses in the casing and the impeller are not taken into account
in the total head.
NAZMY MARKOS 83

HEADS OF A PUMP
3. Manometric Head
It is usually not possible to measure exactly the losses in the
pump casing. So, a term known as manometric head is
introduced. It is the rise in pressure energy of the liquid in the
impeller of the pump.
If two pressure gauges are installed on the suction and the
delivery sides as near to the pump as possible, the difference
in their reading will give the change in the pressure energy in
the pump or the manometric head.
Hm = Manometric head of the pump
Hms = Reading of the pressure gauge on the suction side
Hmd = Reading of the pressure gauge on the delivery side.
Then Hm = Hmd - Hms
NAZMY MARKOS 84

LOSSES AND EFFICIENCIES
1. Hydraulic Efficiency
Hydraulic losses are the losses the occur between the suction
and the delivery ends of a pump.
Hydraulic efficiency varies from 0.6 to 0.9.
2. Manometric Efficiency
Manometric efficiency is defined as the hydraulic efficiency of
an ideal pump.
NAZMY MARKOS 85

3. Volumetric Efficiency
The pressure at the outlet of the impeller is higher than at the
inlet. Thus there is always a tendency on the part of water to
slip back or leak back through the clearance between the
impeller and the casing. There can also be some leakage from
the seals. These are called volumetric losses.
Volumetric efficiency is the ratio of the actual discharge to the
total discharge.
Q = Amount of discharge
Let ∆Q = Amount of leakage.
ηv = Q / (Q+ ∆Q)
Its value lies between 0.97 and 0.98.
NAZMY MARKOS 86

4. Mechanical Efficiency
Mechanical losses in case of a pump are due to
(a) Friction in bearings
(b) Disc friction as the impeller rotates in liquid.
Mechanical efficiency is the ratio of the actual power input to
the impeller and the power given to the shaft.
Let P = Total power input to the shaft
∆ P = Mechanical losses
ηm = (P - ∆ P) / P
Its value lies between 95% - 98%.
NAZMY MARKOS 87

5. Overall Efficiency
It is the ratio of the total head developed by a pump to the
total power input to the shaft.
ηo = (ρQgH) / P
Range of overall efficiency is between 0.71 to 0.86.
NAZMY MARKOS 88

PROBLEM: A CENTRIFUGAL PUMPS DELIVERS 50 LITERS OF WATER PER SECOND TO
A HEIGHT OF 15M THROUGH A 20 M LONG PIPE. DIAMETER OF THE PIPE IS 14 CM.
OVERALL EFFICIENCY IS 72 %, AND THE COEFFICIENT OF FRICTION 0.015.
DETERMINE THE POWER NEEDED TO DRIVE THE PUMP.
Solution:
Hs = 15m
Q=0.05 m3/s
I = 20 m
f = 0.015
d = 0.14 m
ηo = 72%
We have,
ηo = (ρQgH) / P
H = Hs+ Hf + Vd2/(2g)
NAZMY MARKOS 89

PROBLEM:
Solution:
For which Vd is given by,
Q = π/4 d2 Vd
0.05=π/4(0.14)2 Vd
Vd = 3.25 m/s
And hf = (4flVd
2) / (2gd)
hf = (4x0.015x20x3.252)/(2x9.81x0.14)
hf = 4.61 m
H=15+4.61+ 3.252/(2x9.81)= 20.15m
Power to drive pump can be calculated as follows:
ηo = (ρQgH) / P
0.72 = (1000x0.05x9.81x20.15) / P
Or P = 13726 W = 13.726 k W.
NAZMY MARKOS 90

MULTISTAGE PUMPS
To develop a high head, the tangential speed μo has to be
increased. However an increase in the speed also increases the
stresses in the impeller material. This implies that centrifugal pump
with one impeller cannot be used to raise high heads.
More than one pump is needed to develop a high head. The
discharge of one pump is delivered to the next to further augment
the head.
However, a better way is to mount two or more impellers on the
same shaft and enclose them in the same cashing. All the impellers
are put in series so that the water coming out of one impeller is
directed to the next impeller and so on (Fig.10.22).
NAZMY MARKOS 91

MULTISTAGE PUMPS
NAZMY MARKOS 92

CONTROLLING PUMP PERFORMANCE
Changing the amount for friction loss or "Throttling the Pump" will
change the pump's performance
NAZMY MARKOS 93

Head
Pump Flow Rate
PUMP SELECTION
Valve Open
Valve Partially Open
Valve Barely Open
NAZMY MARKOS 94

PIPING DESIGN EQUATIONS
HEURISTICS FOR PIPE DIAMETER
0.494
0.408
0.343
3
:
2.607
:
1.065
,
,1000 /
, /
Liquids
w
D
Gases
w
D
D Diameter inches
w Mass Flowrate lb hr
Density lb ft



 
=  
 
 
=  
 
=
=
=
NAZMY MARKOS 96

ENERGY LOSS IN PIPING NETWORKS
INCOMPRESSIBLE FLUIDS
( ) ( ) ( )
2 2
1 2 1 2 2 1
3
2
2
144 1
2
, /
, /
, /
, 32.174 /s
,
,
L
f
L
P P v v z z h
g
Density lb ft
P Pressure lb in
v Velocity ft sec
g Gravitational Acceleration ft
z Elevation ft
h Head loss ft


− + − = − +
=
=
=
=
=
=
NAZMY MARKOS 97

( ) 2
4
2
2
1
2
2
0.00259
,
,
,
1 ,
L
K Q
h
d
Q Volumetric Flowrate gpm
d Pipe Diameter in
K Sum of all fittings
L
K f straight pipe
D
d
K Sudden enlargement
d
=
=
=
=
=
 
= −
 
 


NAZMY MARKOS 98

FRICTION LOSS FACTORS FOR FITTINGS
Fitting K
Standard 90o Elbow 30fT
Standard 45o Elbow 16fT
Standard Tee
20fT Run
60 fT Branch
Pipe Entrance 0.78
Pipe Exit 1.0
NAZMY MARKOS 99

FRICTION LOSS FACTORS FOR VALVES
2
2
29.9
V
V
d
K
C
C Valve Coefficient
=
=
Valve K
Gate valve 8fT
Globe Valve 340fT
Swing Check Valve 100fT
Lift Check Valve 600fT
Ball Valve 3fT
NAZMY MARKOS 100

FANNING DIAGRAM
f =16/Re

1
f
= 4.0 * log
D

+ 2.28

1
f
= 4.0 * log
D

+ 2.28 − 4.0 * log 4.67
D/
Re f
+1






NAZMY MARKOS 101

ENERGY LOSS IN VALVES
➢ Function of valve type and valve
position
➢ The complex flow path through valves
can result in high head loss (of course,
one of the purposes of a valve is to
create head loss when it is not fully
open)
➢ Ev are the loss in terms of velocity
heads
NAZMY MARKOS 102

CAVITATION
This relationship between velocity and pressure produces some unwelcome effects with respect
to hydraulic machinery, pipes and hydraulic structures.
Considering the total energy of a fluid moving, every time a fluid increases its velocity and
elevation its pressure decreases.
NAZMY MARKOS 103

✓These problems arise when the absolute pressure falls
sufficiently for the small quantity of air that is dissolved in the
water to be released followed by local vaporization of the liquid.
✓The water boils
✓It results in small bubbles of vapour being formed that
gradually get bigger.
✓ When pressure increases they implode.
NAZMY MARKOS 104

PITTING CAUSED BY CAVITATION
This pressure alters the micro structure of the metal, causing
a flake to peel out. Eventually, these microscopic-sized
flukes form a visible pit and, if not repaired, will develop
into major damage.
NAZMY MARKOS 105

✓Bubbles growth and implosion only last a few millisecond but cause
➢ Fatigue and pitting under the continual
repetition of the shocks.
➢ Cavities formation decreases the total
dynamic head produced by the pumps and
thus greatly reduces the mechanical
efficiency.
NAZMY MARKOS 106

The elevation of the pump above the water level in the
suction reservoir – suction head – reduced the inlet
pressure.
This is the most effective way to prevent cavitation,
This is expensive way
NAZMY MARKOS 107

PUMP HEAD DECREASE
No cavitation
Cavitation
NAZMY MARKOS 108

When the bubbles collapse on a metallic surface serious damage occur from prolonged
cavitation erosion.
There is no material resistant to cavitation.
Cavitation is most likely to
occur on the suction side of the
pump.
Noise is generated in the form
of sharp cracking sounds when
cavitation takes place.
NAZMY MARKOS 109

WHEN THE FLUID MOVES
INTO A HIGHER-PRESSURE
REGION, THESE BUBBLES
COLLAPSE WITH
TREMENDOUS FORCE,
GIVING RISE TO PRESSURES
AS HIGH AS 3500 BAR
This is exactly why cavitation is
so important.
NAZMY MARKOS 110

PREVENTING CAVITATION
✓The pressure or head of liquid required to prevent
cavitation on entering the impeller is termed the net
positive suction head NPSH.
NPSH
represents the pressure or head required to force liquid up to the suction pipe to the
impeller.
varies with the speed of rotation and discharge and has to be determined by the
manufacturer from tests.
NAZMY MARKOS 112

THE NET PRESSURE HEAD AT THE INLET SIDE OF THE
PUMP
Hs= static suction head.
hf= friction loss
Zp=elevation of the centreline of the pumps inlet flange
If we add hb atmosphere ( barometric) head and
subtract the vapour head of the fluid hv
NPSH= hs + hb – hv
NPSH = Pump total inlet head above vapour pressure
p
f
s
s z
h
g
v
H
h −
−
−
= 2
2
2
NAZMY MARKOS 113

To avoid cavitation a certain amount of NPSH is
required by the pump.
fpump
p
fpipe
v
b h
g
v
z
h
h
h +

−
−
−
2
2
2
NPSHA
Characteristic
of the system
and of the fluid
hv(T)
>
NPSHR
Represents the minimum
positive absolute head which must
be supplied at the pump suction
flange in order to overcome friction
losses due to the eye and the vanes
of the impeller and takes into
account the velocity head too.
NAZMY MARKOS 114

IF NPSHA > NPSHR
The pump cavitates and it will operate at
a reduced discharge
To avoid cavitation the philosophy
can be summarized in
1.Keep velocity low and pressure high.
2.Reduce head losses.
NAZMY MARKOS 115

NPSHC AND H-Q
✓determine the normal head-
flow.
✓Induce head losses by
throttling at the inlet section.
✓the performance curve will fall
away from the normal operating
point.
✓(NPSH)c = NPSH before
cavitation occurs (incipient
cavitation) is calculated at the
point at which the head H drops
below the normal operating
characteristic by some
arbitrarily selected percentage,
2 or 3 per cent
NAZMY MARKOS 116

Vapour
Water
Vapour pressure, tv versus temperature, t
kPa
)
(
900
3
.
10 m
h
h elevation
b −
=
Barometric head, hb versus height above see level
NAZMY MARKOS 117

Cavitation test
Incipient cavitation Critical cavitation
NAZMY MARKOS 118

A cavitation parameter is defined as pump total inlet head
above vapour pressure pvap divided by the head H developed
by pump at the pump inlet flange
H
NPSHA
H
g
p
g
V
g
p vap
i
i
a =
−
+
=



2
2
H
Permitted cavitation
Economical construction
R
avaliable 
 
Design criteria
NPSHA > NPSHR
NAZMY MARKOS 119

1 - Critical cavitation (efficiency and head drop)
2 - Incipient cavitation (air bubbles observation)
Pump cavitation characteristics in
normal zone of operation
NPSH
Q (m3/s)
NAZMY MARKOS 120

1. Noise
2. Vibrations
H - head
 - efficiency
N - power
db db
Noise and vibration of a pump
NAZMY MARKOS 121

FOR THE PUMP LAYOUT
✓Position the pump below the level of liquid supply .
✓Reduce suction lift hs to small values.
✓Friction and minor losses result in a loss of pressure
so design the suction pipe with as few bends and
constrictions as possible.
✓Suction pipelines should be sloped to avoid air
pockets that generate local head losses.
NAZMY MARKOS 122

FOR THE PUMP LAYOUT
✓Select either a different pump or a different
arrangement of pumps.
✓Use a generously sized suction pipe to deliver
the liquid from the wettwell to the pump, to keep
velocity low and pressure high.
✓ Design the sump so that the liquid does not
rotate in the suction pipe.
NAZMY MARKOS 123

METHODS OF IMPROVING UNFAVORABLE
SUCTION CONDITIONS
✓Raise the upstream reservoir water level.
✓Lower the pump.
✓Use lower pump speeds (lower speed pumps are
more expensive to operate than high speed
pumps).
✓Use a double suction impeller.
NAZMY MARKOS 124

METHODS OF IMPROVING UNFAVORABLE
SUCTION CONDITIONS
✓Use a larger impeller eye area.
✓Use an oversized pump, risky.
✓Use an inducer, it requires less NPSH.
✓Use a booster pump.
✓Subcool the liquid. By reducing temperature one
reduces its vapour pressure.
NAZMY MARKOS 125

Arrangement A1” above is
considered for medium
sized pumps having suction
line size around and below
10 inch. The suction strainer
is placed between the
isolation valve and flange.
Suction Line is supported
with trunion and from
structures available above.
Discharge line is taken
vertically to clear headroom
and supported from above.
Concentric reducer if
needed is placed in the first
removable spool. Check
valve and isolation valve are
placed immediately after.
From pump nozzle to first
elbow a minimum 3 to 5
diameter straight length to
be there including length of
reducer where possible.
NAZMY MARKOS 127

“Arrangement B1” above is
an alternate arrangement
used instead of
“Arrangement A1” (a) For
larger line sizes with higher
pressure ratings when the
block valve hand wheel
becomes too high to
operate. (b) When
check valves to be installed
in horizontal position for
e.g. lift check valve will
work in horizontal position
only.
Here the discharge line is
rolled as suitable so that the
supporting will come out of
foundation area. And the
line is supported with
trunion at elbow.
NAZMY MARKOS 128

End Suction Top discharge pump piping-
“Arrangement C1”
“Arrangement D1”
n similar fashion “Arrangement C1 & D1” are used when the pump is used for two
different services. Here on suction line the service B line is connected after main
isolation valve for service A as shown above. And on discharge line it is connected
after the common check valve.
NAZMY MARKOS 129

End Suction Top discharge pump piping-“Arrangement E1”
“Arrangement E1” above is used for larger pumps and for critical services where
straight length requirement is anticipated. This arrangement also is more operation
and maintenance friendly. Suction and discharge Lines are supported from floor.
NAZMY MARKOS 130

“Arrangement F1”
“Arrangement G1”
“Arrangement F1 & G1” are slight variation of the previous arrangement which is
used for hot lines that require more flexibility. Its a common practise to have a
suction and discharge header near pump and branches to and from pump is
connected to this header, the above arrangement depict that.
NAZMY MARKOS 131

“Arrangement H1” can be
followed for larger lines where
the valve elevation requires a
platform to operate.
NAZMY MARKOS 132

WATER HAMMER
PHENOMENON IN PIPELINES
A sudden change of flow rate in a large pipeline (due to valve
closure, pump turnoff, etc.) may involve a great mass of water
moving inside the pipe.
The force resulting from changing the speed of the water mass
may cause a pressure rise in the pipe with a magnitude several
times greater than the normal static pressure in the pipe.
The excessive pressure may fracture the pipe walls or cause
other damage to the pipeline system.
This phenomenon is commonly known as the water hammer
phenomenon
NAZMY MARKOS 141

SOME TYPICAL DAMAGES
Pipe damage in
power station Okigawa
Burst pipe in power
sation Big Creek #3, USA
Pump damage in Azambuja
Portugal
NAZMY MARKOS 142

WATER HAMMER
Consider a long pipe AB:
 Connected at one end to a reservoir containing water at a height H from the center of the pipe.
 At the other end of the pipe, a valve to regulate the flow of water is provided.
NAZMY MARKOS 144

If the valve is suddenly closed, the flowing water will
be obstructed and momentum will be destroyed and
consequently a wave of high pressure will be
created which travels back and forth starting at the
valve, traveling to the reservoir, and returning back to
the valve and so on.
This wave of high pressure:
1. Has a very high speed (called celerity, C ) which
may reach the speed of sound wave and may create
noise called knocking,
2. Has the effect of hammering action on the walls of
the pipe and hence is commonly known as the water
hammer phenomenon.
NAZMY MARKOS 145

The kinetic energy of the water moving through the pipe
is converted into potential energy stored in the water
and the walls of the pipe through the elastic deformation
of both.
The water is compressed and the pipe material is
stretched.
The following figure illustrates the formation and
transition of the pressure wave due to the sudden
closure of the valve
NAZMY MARKOS 146

PROPAGATION OF WATER
HAMMER
PRESSURE WAVE
Steady state condition
Transient condition t < L/C
NAZMY MARKOS 147

Transient condition t = L/C
Transient condition L/C >t >2L/C
Transient condition t =2L/C
NAZMY MARKOS 148

Transient condition t = 3L/C
Transient condition 2L/C >t >3L/C
NAZMY MARKOS 149

Transient condition 3L/C >t >4L/C
Transient condition t = 4L/C
NAZMY MARKOS 150

ANALYSIS OF WATER HAMMER
PHENOMENON
The pressure rise due to water hammer depends upon:
(a) The velocity of the flow of water in pipe,
(b) The length of pipe,
(c) Time taken to close the valve,
(d) Elastic properties of the material of the pipe.
The following cases of water hammer will be considered:
 Gradual closure of valve,
 Sudden closure of valve and pipe is rigid, and
 Sudden closure of valve and pipe is elastic.
NAZMY MARKOS 151

The time required for the pressure wave to travel from the
valve to the reservoir and back to the valve is:
Where:
L = length of the pipe (m)
C = speed of pressure wave, celerity (m/sec)
If the valve time of closure is tc , then
➢ If the closure is considered gradual
➢ If the closure is considered sudden
t
L
C
=
2
t
L
C
c 
2
C
L
tc
2

NAZMY MARKOS 152

The speed of pressure wave “C” depends on :
 the pipe wall material.
 the properties of the fluid.
 the anchorage method of the pipe.
if the pipe is rigid
if the pipe is elastic
and

b
E
C=

c
E
C=
e
E
K
D
E
E p
b
c
+
=
1
1
NAZMY MARKOS 153

Where:
C = velocity (celerity) of pressure wave due to water hammer.
= water density ( 1000 kg/m3 ).
Eb = bulk modulus of water ( 2.1 x 109 N/m2 ).
Ec = effective bulk modulus of water in elastic pipe.
Ep = Modulus of elasticity of the pipe material.
e = thickness of pipe wall.
D = diameter of pipe.
K = factor depends on the anchorage method:
= for pipes free to move longitudinally,
= for pipes anchored at both ends against longitudinal movement
= for pipes with expansion joints.
where = poisson’s ratio of the pipe material (0.25 - 0.35). It may take the
value = 0.25 for common pipe materials.

( )
5
4
− 
( )
1 2
−
( . )
1 05
− 


NAZMY MARKOS 154

The Maximum pressure created by the water hammer
NAZMY MARKOS 156

CASE 1: GRADUAL CLOSURE OF
VALVE
If the time of closure , then the closure is said to be gradual and
the increased pressure is
where,
V0 = initial velocity of water flowing in the pipe before pipe closure
t = time of closure.
L = length of pipe.
= water density.
The pressure head caused by the water hammer is
t
L
C
c 
2
 P
LV
t
=
 0



H
P LV
gt
LV
gt
= = =



0 0
NAZMY MARKOS 157

( )
N
P
P N
N
o +
+
=
 4
2
2








=
t
P
LV
N
o
o

Another method for closure time (t > 2 L/C)
NAZMY MARKOS 158

CASE 2: SUDDEN CLOSURE OF VALVE
AND PIPE IS RIGID
If the time of closure , then the closure is said to be Sudden.
The pressure head due caused by the water hammer is
But for rigid pipe so:
t
L
C
c 
2
 H
C V
g
= 0

b
E
g
V
H 0
=


b
E
V
P 0
=

0
CV
P 
=


b
E
C=
NAZMY MARKOS 159

CASE 3: SUDDEN CLOSURE OF VALVE
AND PIPE IS ELASTIC
If the time of closure , then the closure is said to be Sudden.
The pressure head caused by the water hammer is
But for elastic pipe so:
t
L
C
c 
2
 H
C V
g
= 0
0
CV
P 
=

)
1
(
1
0
e
E
K
D
E
g
V
H
p
b
+
=


)
1
(
0
e
E
K
D
E
V
P
p
b
+
=



c
E
C=
NAZMY MARKOS 160

Applying the water
hammer formulas we
can determine the
energy gradient line
and the hydraulic
gradient line for the
pipe system under
steady flow condition.
Water Hammer Pressure in a Pipeline
So the total pressure at any point M after closure (water hammer) is
P P P
M M before closure
= +
, 
or
H H H
M M before closure
= +
, 
Water hammer pressure head
HA

P
HA

=

Due to
water
hammer
NAZMY MARKOS 161

TIME HISTORY OF PRESSURE WAVE
(WATER HAMMER)
The time history of the pressure wave for a
specific point on the pipe is a graph that simply
shows the relation between the pressure increase
( ) and time during the propagation of the
water hammer pressure waves.
 P
NAZMY MARKOS 162

For example, considering point “A” just to the left of the valve.
Note: friction (viscosity) is neglected.
Time history for pressure at point “A” (after valve closure)
1
NAZMY MARKOS 163

THE TIME HISTORY FOR POINT “M” (AT
MIDPOINT OF THE PIPE)
1
NAZMY MARKOS 164

THE TIME HISTORY FOR POINT B (AT A DISTANCE X
FROM THE RESERVOIR )
1
This is a general graph where we can substitute any value
for x (within the pipe length) to obtain the time history for
that point.
t*(2L/C)
NAZMY MARKOS 165

In real practice friction effects are considered and hence a
damping effect occurs and the pressure wave dies out, i.e.;
energy is dissipated.
the time history for pressure at point “A”
when friction (viscosity) is included
Damping effect of friction
t*(2L/C)
NAZMY MARKOS 166

STRESSES IN THE PIPE WALL
After calculating the pressure increase due to the
water hammer, we can find the stresses in the pipe
wall:
Circumferential (hoop) stress “fc :
”
Longitudinal stress “fL”:
f
P D
t
c
p
=
2
f
P D
t
L
p
=
4
where:
D = pipe inside diameter
tp = pipe wall thickness
P P P
= +
0  = total pressure
= initial pressure (before valve closure) +
pressure increase due water hammer.
NAZMY MARKOS 167

To keep the water hammer pressure within
manageable limits, valves are commonly design
with closure times considerably greater than
2L/C
NAZMY MARKOS 170

EXAMPLE
A cast iron pipe with 20 cm diameter and 15 mm wall thickness is
carrying water from a reservoir. At the end of the pipe a valve is
installed to regulate the flow. The following data are available:
e = 0.15 mm (absolute roughness) ,
L = 1500 m (length of pipe),
Q = 40 l/sec (design flow) ,
K = 2.1 x 109 N/m2 (bulk modulus of water),
E = 2.1 x 1011 N/m2 (modulus of elasticity of cast iron),
= 0.25 (poisson’s ratio),
= 1000 kg/m3
T = 150 C.


NAZMY MARKOS 171

Find , , fc , and fL due to the water hammer
produced for the following cases:
a) Assuming rigid pipe when tc = 10 seconds, and tc = 1.5 seconds.
b) Assuming elastic pipe when tc = 10 seconds, and tc = 1.5
seconds, if:
1. the pipe is free to move longitudinally,
2. the pipe is anchored at both ends and throughout its length,
3. the pipe has expansion joints.
c) Draw the time history of the pressure wave for the case (b-3) at:
1. a point just to the left of the valve, and
2. a distance x = 0.35 L from the reservoir.
d) Find the total pressure for all the cases in (b-3).
 P  H
NAZMY MARKOS 172

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