Pumps
Irrigation pumps lift water from an existing
source, such as surface or groundwater to a
higher level.
They have to overcome friction losses during
transport of the water and provide pressure for
sprinkler and drip irrigation.
Irrigation pumps are mechanical devices which
use energy from electrical or combustion motors
to increase the potential and (or) kinetic energy of
the irrigation water.
……Pumps
Pumps are used in irrigation systems to impart a head
to the water so it may be distributed to different
locations on the farm and used effectively in application
systems.
The key requirement in pump selection and design of
pump systems for typical irrigation installations is that
there is a correspondence between the requirements of
the irrigation system and the maximum operating
efficiency of the pump.
Requirements of irrigation system are:
- flow rates
- pressure out put necessary to operate the system.
Principles of Water lifting
1. Direct lift (Direct lift devices)
physically lifting water in a container
2. Displacement (Displacement pumps)
This involves utilizing the fact that water is
(effectively) incompressible and can therefore be
'pushed' or displaced.
- Rotary positive displacement pumps, which use
gears, vanes, lobes or screws to move, discrete
quantities of water from the inlet to the outlet of the
pump.
- Reciprocating positive displacement pumps: piston pumps,
plunger pumps, diaphragm pumps.
3. Gravity (Gravity Device)
– Gravity operated systems, Siphons
4. Creating a velocity head (velocity
pumps

Rotodynamic pumps: volute centrifugal
pumps, turbine centrifugal pumps,
regenerative centrifugal pumps.
Types of pumps
Pumps used in irrigation systems are available
in a wide variety of pressure and discharge
configurations.
Pressure and discharge are inversely related
in pump design , so pumps which produce
high pressure have relatively small discharge
and vice versa.
Characteristics of centrifugal , turbine and
propeller pumps is given as below.
Impeller design and pump characteristics as
function of specific speed
In the above figure,
 Flow enters the pump from the bottom.
 In centrifugal pump , energy is imparted to the flow by
the impeller which directs the flow radially outward.
 Centrifugal pumps have high heads but limited
discharge.
 Francis impeller – deliver intermediate flow rates but
there is less energy available to pressurize the fluid.
 Propeller type system is able to deliver large flow
volumes but is capable of imparting a very small
pressure differential to the fluid.
Specific Speed - Ns
 Means of quantitatively categorizing the
operating characteristics of a pump.
N
s

 Q 0.5
 0.2108N
0.75
H







Where: Ns = specific speed , dimensionless
N = Revolutionary speed of pump , rpm
Q = Pump discharge , L /min
H = discharge pressure head , m
Fig. Impeller shape &maximum efficiency as
function of Ns
 Ns varies from 500 (centrifugal pump) to
10, 000 (propeller pump).
The Ns of a pump is closely related to the maximum
operating efficiency of the pump.
Operating efficiency : ratio of the power imparted by
the impeller to the water compared to the power
supplied to the pump by the motor.
The performance curve indicates that careful attention
must be given to the discharge requirements of the
pump , which determine the specific speed, so the
most suitable pump may be selected.
Classification of pumps
1. Reciprocating positive displacement pumps
• use back and forth movement of mechanical parts
 Water is for most practical purposes incompressible.
Consequently, if a close fitting piston is drawn through
a pipe full of water, it will displace water along the
pipe.
 Similarly, raising a piston in a submersed pipe will
draw water up behind it to fill the vacuum which would
otherwise occurs.
 Basic relationships between the output or
discharge rate (Q), piston diameter (d), stroke or
length of piston travel (S), number of strokes per
minute (n), and the volumetric efficiency, which is
the percentage of the swept volume that is
actually pumped per stroke ( η vol )

πd 2
Swept area of the piston is A =
4
The swept volume per stroke will be V= AS
The discharge per stroke will be
q=Vη
vol
The pumping rate (per minute) is Q = nq
2. Rotary positive displacement pumps
• These are group of devices which utilizes the
displacement principle for lifting or moving
water, but which achieve this by using a
rotating form of displacer (gears, vanes, lobes
or screws).
• use gears and vanes to move discrete part of
water.
• These generally produce a continuous, or
sometimes a slightly pulsed, water output
these pumps tend themselves readily to
mechanization and to high speed operation
than reciprocal displacement pumps.
3. Rotodynamic (centrifugal) pumps
• use the centrifugal force of rotating
devices (called impellers) to increase the
kinetic and pressure energy of the water.
• Depends on propelling water using a
spinning impeller of rotor.
• There are two main types of rotodynamic
pumps (centrifugal pumps), i.e.
– Volute centrifugal pumps
– Turbine centrifugal pumps
 Reciprocating and rotary pumps are called
positive displacement pumps, while
centrifugal pumps are called variable
displacement pumps in which the
delivery head varies with the quantity of
water pumped.
Axial flow pump
Radial flow (Centrifugal pumps)
Typical mixed flow pump
PUMPING THEORY-CENTRIFUGAL PUMPS
 In centrifugal pumps the energy is imparted to the
water by a unit of rotating vanes called an impeller,
which are located in a stationary body called the
casing.
CASING
Water is pushed into the center or eye of the impeller by
atmospheric or water pressure and set into a rotary
motion by the impeller.
-The rotating movement causes a centrifugal force to act
upon the water, which drives the water outward,
between the vanes of the impeller, into the
surrounding casing from where it moves to the pump
outlet.
-Different types of casing: a)Single volute, (b) Double
volute, and (c). Diffuser turbine casing.
IMPELLERS
 Impellers can be classified according to the direction
of flow through the impeller in relation to the axis of
rotation as (a) radial, (b) axial or (c) mixed flow.
 Where high flows at low heads are required (which is
common with irrigation pumps), the most efficient
impeller is an axial flow one.
 Impellers can also be classified according to their
design into (a) open (consist only vanes attached to
the hub with out shroud/side-wall), (b) semi-open
(have one shroud) and (c) enclosed (have shrouds
(sidewalls) enclosing the waterways between vanes)
impellers as shown in figure.
Impellers
CENTRIFUGAL PUMP PERFORMANCE

Pumping capacity, pumping head, power, efficiency
and net positive suction head are the main
parameters, which describe the performance of a
pump.
1.Pump capacity:
The capacity of a pump is the volume of water (Q) which
the pump can deliver per unit of time, e.g. in litters per
second (lt/s) or cubic meters per hour.
2. Pumping Head
The actual pumping head imposed on a pump, gross
working head, will be somewhat greater than the
actual vertical distance, or static head, water has to be
raised.
 The pumping head (H) is the net work done on a unit
of water by the pump. It is expressed by the
Bernoulli’s equation.
 H = (p/(g) + V2/(2g) + Z)d - (p/(pg) + V2/(2g) + Z)s
P = Water pressure in (kpa or meters water column)
 = density of the fluid in (kg/m3)
g = acceleration due to gravity in (m/S2)
V = Water velocity in (m/s)
Z = Elevation head in meters relative to a reference level or
datum.
g =  =specific weight of the fluid (kN/m3)
Power

The amount of energy (in joule) applied per
unit of time (seconds) is the power imparted to
the water in joule/ second = Watt.
Phydr =  g H Q = HQ

Phydr = hydraulic or water power in Watt.
Q = pumped volume in m3/s.
Pumping at a rate of 180m3/ h at a head of
120 meters require:
Phydr = 1000 x 9.81 x 120 x 180/3600 = 4, 905 watt = 4.9
kw
Pump Efficiency
The actual power and energy needs are always greater
than the hydraulic energy needed
 Therefore, the pump efficiency (pump) is the percent of
power input by a motor (in kw) to the pump shaft (the
so-called brake power) which is transferred to the
water:
hydr = (Phydr / Pmotor)x 100
hydr = pump efficiency
Phydr = water power (kw, hp)
Pmotor = break power (kw, hp)
Pump Power Requirements
 The power added to water as it moves through a
pump can be calculated with the following formula:
WHP = Q x TDH
3960
where: WHP = Water Horse Power
Q = Flow rate in gallons per minute (GPM)
TDH = Total Dynamic Head (feet)
Break Horse power
BHP =
WHP
Pump Eff. x Drive Eff.
BHP -- Brake Horsepower (continuous horsepower rating of the
power unit).
Pump Eff. -- Efficiency of the pump usually read from a pump
curve and having a value between 0 and 1.
Drive Eff. -- Efficiency of the drive unit between the power source
and the pump. For direct connection this value is 1, for right
angle drives the value is 0.95 and for belt drives it can
vary from 0.7 to 0.85.
Net Positive Suction Head- NPSH
 The net positive section head (NPSH) is the amount
of energy required to prevent the formation of vapor
filled cavities within the eye of the single and fires
stage impellers.
 This cavities which form when pressure within the
eye drop below the vapor pressure of water collapse
within higher-pressure areas of the pump.
 The formation and subsequent collapse of these
vapor filled cavities is called cavitation.
 When cavities collapse occur violently at interior
surfaces of the pump they produce ring-shaped
indentations in the surface called pits. Continued
pitting severely damage pumps, and must be
avoided
 The NPSH required to prevent cavitation is a function
of pump design and is usually determined
experimentally for each pump.
 Cavitation is prevented when heads (available NPSH)
within the eye of single and first impeller exceeds the
NPSH, value published by the manufacturers.
 The available NPSH is a function of the
atmospheric pressure, vapor pressure, friction
loss, suction head and should always exceed
the NPSH specified by the pump manufacturer
with at least 0.5 to 1.0 meters of head.
NPSH = Ha - Hs - Hf –Hvp
Ha = atmospheric pressure on the surface of the water
(in m)
Hs = elevation of the water above or below the impeller
eye while pumping (in m) (if the level is above the eye,
Hs is positive, if the level is below the eye, Hs is
negative)
Hf = friction-head losses in the suction piping (in m)
Hvp = Vapor pressure of the water at the pumping
temperature (in m).
 The vapor pockets, which form when pressures within
the eye of the impeller drop below the vapor pressure
of the water, subsequently collapse violently within the
high pressure areas of the pump.
 This collapse is called cavitation and can cause
severe damage to the pump. Operate the pump with
in its design capacity.
PERFORMANCE CURVES




Head versus pump capacity.
Efficiency versus pump capacity.
Brake power versus pump
capacity.
NPSH versus pump capacity.
AFFINITY LAWS
 The performance of a pump varies with the speed at
which the impeller rotates. Theoretically, varying
the pump speed will result in changes in flow rate,
TDH and BHP according to the following formulas:
 For a constant Diameter
Q2= Q1 x (N2/N1)
H2 = H1 x (N2/N1) 2
BP2= BP1 x (N2/N1) 3
NPSH2 = NPSH1 x (N2/N1) 2
……Affinity Laws
For constant N ( Rotation per minute)
Q2 = Q1 x (D2/D1)
H2 = H1 x (D2/D1) 2
BP2 = BP1 x (D2/D1) 3
NPSH2 = NPSH1 x (D2/D1)2
where
Q = discharge
N=number of Revolution per minute
BP = Break power
NPSH = Net positive suction head
D = diameter
H = Available head
Pump performance curves
H
Q
Typical Pump performance curve
Pump operation point
 A centrifugal pump operates at combinations of
head and discharge according to its H-Q
characteristic performance curve. The
particular combination of H-Q at which a pump
is operating is the pump’s operating point.
Power requirement, efficiency and NPSH for the
pump can be determined once the operating
point is known.
 The specific operating point depends on the
head and water volume requirements of the
irrigation system. A system curve describes
the H–Q performance of the irrigation system.
 The system curve is then combined with the HQ characteristic curve of the pump to determine
the operating point.
….Pump operation point
 Operating points can be altered by
changing either the H-Q curve for the
pump or for irrigation system. Pump can
be altered by changing the pump speed or
the impeller diameter (see the Affinity
Laws).
Shifting pump operation point
Pump curve for 2000rpm
Pump curve for 1800 rpm
H
Pump operation point
Q
This is the point where the H-Q requirements of the irrigation system
are equal to the H-Q produced by the pump.
 The system curve is constructed by calculating the system
head Hs required by the irrigation to deliver varying
volumes of water per unit of time.
 The system head Hs is calculated with the formula
Hs = SL+ DL+ DD+ H1 + M1 +HO + VH
Where:
HS = System head (m)
SL = Suction lift from static water level (m)
DL = discharge lift from pump to highest discharge point
(m)
DD = draw down in water source (m)
H1 = head loss in delivery pipes (m)
M1 = minor losses in fittings (m)
Ho = operating head (m)
VH = velocity head (m)
Total Dynamic Head
 The total dynamic head of a pump is the sum of the
total static head, the pressure head, the friction head,
and the velocity head.
TDH =Z +Hs + hv + hf
 Total Static Head
 The total static head is the total vertical distance the pump must
lift the water. When pumping from a well, it would be the
distance from the pumping water level in the well to the ground
surface plus the vertical distance the water is lifted from the
ground surface to the discharge point. When pumping from an
open water surface it would be the total vertical distance from
the water surface to the discharge point.
Static Head
Water Horse Power (WHP)
WHP = Q γH
WHP = the energy pump produces to move the water
BHP = Input power to the pump given by the motor
= out put of the motor
Input power for the motor is from electricity.
P = Q H Sg
4634 E
Where:
P = power , metric horse power
Q = Pump discharge, L/min
H= Discharge pressure head, m
Sg =specific gravity of fluid, dimensionless
E = pump efficiency , fraction
P=
P=
Q H Sg
278.04 E
Q H Sg
0.102 E
P = Q x TDH Sg
3960 E
Where Q = m3/hr
Where P = power , KW
Q = discharge , m3/s
Where P = power, brake horse power
(bhp)
Q = pump discharge , (gpm)
TDH or H = Discharge pressure head
, ft
Water Horse Power (WHP)
WHP = Q  H
WHP = the energy pump produces to move the water
BHP = Input power to the pump given by the motor
= out put of the motor
Input power for the motor is from electricity.
input
Motor
BHP
Em
Pump
Ep
EPP
WHP
Pump efficiency
Ep = WHP / BHP
Em = BHP/ input
EPP = WHP/ input = Ep . Em
Where Em = Efficiency of motor
Ep = efficiency of pump
EPP = Efficiency of pumping plant
Combination of pumps
Pumps in parallel
- To provide more Q and not more head
Q = Q1 + Q2 + Q3
Q
P1
P2
Q2
Q1
River
P3
Q3
Pumps in series
To Create more head. This is so by using
submersible pumps.
Q
P3
Q
H = H1 + H2+ H3
P2
Q
P1
Q
Water Source
In Submersible pump a number of impellers are
connected in series
NPSH
 The head which let water flow through the
suction pipe in to the pump.
 NPSH required - is the head required at the inlet of the
impeller to insure that the liquid will not boil or form
vapour pockets which will result in cavitation.
NPSHavial. = Patm - Zs- PV – hfs
atm. Pressure - static suction head - vapor pr/ head - friction head loss
 The height to which the pump has to be raised should
be low in order not to cause cavitation.
 To Estimate Zs , assume NPSHavail. = NPSHreq.
Pump Selection
Process of choosing the most suitable pump for
the irrigation system.
It involves the specification of the discharge
and pressure requirements of the irrigation
system, selecting the required pumping method
and identifying the different pumps (within the
chosen method), which can meet the
requirements of the irrigation system.
 financial Criteria
 management Criteria.
PEREFORMANCE REQUIREMENTS
 The discharge and head requirements of the
irrigation system are a function of :
 CWR in the different stages of growth,
 The size of the land to be irrigated,
 The method of irrigation
 The system layout
Discharge –Head requirement of the irrigation
system must agree with Discharge head
requirement of the operating system (pump)
Identifying suitable pumps
 The horizontally installed volute suction pump and the
vertical diffuser (turbine) pumps are the most suitable
and most commonly used pumps with irrigation
systems.
 Horizontal volute suction pumps are usually cheaper
and easier to install than vertical pumps.
 Vertical turbine pumps, which are positioned below the
water level, are used in deep wells or when the water
level is too far from a suitable surface pump positions
to accommodate the NPSH requirements.
 Vertical pumps are sometimes also used to eliminate
the need for priming of horizontal pumps
 The pump’s required NPSH is given by the
pump characteristic curves provided by the
manufacturer.
 The available NPSH must then be determined
under local conditions and compared to the
required NPSH, whereby the available should
be at least 0.5 to 1.0 m more than the required
NPSH.
 What if the available NPSH is less than the
required NPSH in Vertical Turbine pumps?
Increase the depth of submergence….
Consult manufacturer’s criteria (pump
characteristic curve) to select suitable pump.
Selection Criteria must consider:
 Financial constraints – Economy
 Tangible benefits – not quantified in monetary
terms reliability ,availability of spare parts ,
maintenance skills
Proper analysis of investment (fixed costs) &
operational costs.
The cheapest system is not always the
best, since low investment costs often
result in high running costs !!!
 Investment in a pumping system should not be
considered as one-off cash expenditure.
 The current value of the money compared to its
future value, taking into account interest rates
(a), inflation (i) and the annual repayment of the
loan. Spread out over the life cycle (n) of the
pumping system (pump and motor)annulization.
Step-by-step procedure of costing irrigation pumps
1.Calculate the hydraulic energy requirements
each month
2. Determine the design month
Size the pump and Power source
4. Determine the installed capital cost of the whole
System
5. Determine the present worth of the recurrent costs, sub-divided into
a. Replacement costs
b. Maintenance costs
c.Operating costs
6. Life cycle costs
7. Unit water cost





Operating costs
Energy, maintenance and repair cost are generally
considered recurrent operating or running costs.
The energy costs are a function of the load on the
pump and the operating time per year.
A pump will not necessarily operate under the same
head and discharge requirements during the whole
year.
In this case the hydraulic power requirement and
efficiency of the pump will differ and therefore the
brake or motor power also vary.
The respective motor power requirement times the
respective operating hours per year will suggest the
kwh /year
 Annual maintenance and repair costs may also be
budgeted as a percentage of the original investment
cost.
OTHER COSTS
distribution system,
the intake or borehole,
pump house,
personnel costs, etc
-AVAILABILITY OF TECHNOLOGY AND SPARES
-OPERATIONAL CONVENIENCE- skilled man
-Reliability
Must be included in the cost estimation
Pump installation
Pump house
When a pump is selected one of the criteria
influencing the selection process will be the
available space and intended position of the
pump.
will the pump be suction pump, mounted at the
surface?
will it be a turbine pump with only the motor at the
surface?
will the motor and pump be submerged below the
water?
In the case of surface pumps, will it be a mobile or
a permanent installation?
Guidelines for permanent pump installations
 The place where the pump will be located will
need to be easily accessible;
 In most cases it will be an advantage to have
the pump, motor and /or switchboard located
in a pump house for the simple sake of
protection (weather/theft/destruction);
 The pump house will need to be large enough
for installation, maintenance and repair
activities;
 For the bigger equipment there should be the
possibility of lifting equipment being installed
to move the pump;
 Drainage facilities should be provided for spill
water when the pump is being dismantled;
 Special needs to be given to lighting and
ventilation and – in the case of below zero
temperatures-heating;
 Pump installations near inhabited areas will
require a form of noise protection;
Installation
 Mobile pump installations may be trailer mounted or
connected to, for example, a tractor.
permanent pumping installations.
 Horizontal pumps are usually constructed with their
motor on one steel base plate or frame .
 With permanent installations the pump and motor will
be positioned on a reinforced concrete slab.
 The slab should be constructed in such a manner that:
 it is large enough to fit the whole pump& motor
 it is strong enough to carry the weight of the pump&
motor.
 during operation no vibration occurs
 To avoid motor and pump vibrations to be
transmitted to the floor of the pump house, a
50mm thick cork or rubber layer can be
included in the slab.
ALIGNMENT
 It is essential that motor and pump are aligned
precisely. If this is not the case additional forces
will come out in the bearings of both and cause
overheating and eventually the system will
brake down.
 Proper alignment is also essential with the use
of vertical turbine pumps to avoid damage to
the bearings of the pump and motor.

Consolidation or settlement of the soil can also cause
misalignment after a pump has been in installed.
Regular checking of pumping unit and pipeline
connections should be carried out to avoid potential
damage.
ELECTRICAL CONNECTIONS
 With electrical motor units extreme care should be
taken to properly protect and insulate the electrical
cables, connections and switches. The unit should
be properly grounded.
PIPE CONNECTIONS
 The correct installation and connection of the
suction and delivery pipes to the pump unit is
equally important.
 Many pump failures can be attributed to
incorrect or imprecise suction conditions.
Some guidelines are:
 the suction line should be as short as possible;
 the suction line should rise to the pump to
avoid air pockets. If unavoidable, filling/air
valve has to be fitted (see figure 6.4);
 the suction line should have as few bends as
possible and bends should have a wide radius
 suction lines should have a side diameter;
 contractions should be eccentric to avoid air
pockets
 Suction lines should have absolutely no
leakages;
 Non-self priming pumps should have a widediameter foot valve at the Inlet side of the
suction pipe;
 A low-resistance restrainers should be fitted to
avoid contamination from entering the pump,
while avoiding excessive friction loss;
 Adequate submergence below the lowest
water level to avoid the intake of air at the
inlet;
DELIVERY PIPE
 Regulations for the delivery system are less
strict than for the suction line.
 Non –return valve should be fitted after the
pump if the delivery line remains under
pressure after the pump is turned off;
 A control valve can be fitted:
– inspection and repair;
– pump to be started under a no-flow conditions;
– to (occasionally) regulate the flow in the delivery
system. Note that this should never be done by a
valve in the suction line!
 With positive displacement pumps it is essential
to include a safety valve between the pump and
the control valve.
WATER HAMMER
 When water is flowing through a distribution
system a sudden change in the flow velocity
can cause extreme pressure changes.
 A change in the flow can be the result of
closing a valve or the turning off of the pump.
 This pressure is transmitted throughout the
pipeline and reverses direction as soon as it
reaches the end of the line.
 At the opposite end a corresponding negative
pressure will occur. Both the positive and
negative pressure can cause severe damage
to the pipelines.
 The water hammer can be reduced as follows:
1. by reducing the normal flow velocity through
the system by choosing larger diameter pipes;
2. Reducing the speed with which the flow in the
system can be changed by:
=>using slow control valves
=>using air pressure tanks –as buffer
MOTOR
 When pump and motors are purchased separately
it is important to follow the manufacturer’s
instructions for motor installation carefully.
 Care should be taken that the capacity of the
supply is sufficient to run the motor and that the
wiring used is according to the specifications of the
manufacturer.
 Before starting the motor the lubrication of pump
and motor should be checked against the
manufacturer’s instructions.
 After this the rotation direction of the motor must
be checked.

With many pumps only one direction of rotation is
permissible because otherwise bearings, seals and
couplings may become loosened and disconnected.
PRIMING



With non-self-priming pumps the pump and the
whole suction line have to be filled with water before
the pump can be functional. In places where air
accumulates in the system the air should be
released.
If the level is higher than the pump, the opening of
the air valve will be sufficient to fill the suction line
and pump with water;
When there is no gravity flow to the pump three other
methods are commonly used:
 A. from an outside source with a funnel;
 B. via a return line with check valve from the delivery
system
 C. With a vacuum pump
 With self-priming pumps generally only the
pump has to be filled with water. In
exceptional cases with long suction lines
or high suction lifts extra water may need
to be added. This will be specified in the
manufacturer’s instructions.
 Intake structures