PumpsPumpsIrrigation pumps lift water from an existing Irrigation pumps lift water from an existing source, such as surface or groundwater to a source, such as surface or groundwater to a higher level.higher level.

They have to overcome friction losses during They have to overcome friction losses during transport of the water and provide pressure for transport of the water and provide pressure for sprinkler and drip irrigation. sprinkler and drip irrigation.

Irrigation pumps are mechanical devices which Irrigation pumps are mechanical devices which use energy from electrical or combustion motors use energy from electrical or combustion motors to increase the potential and (or) kinetic energy of to increase the potential and (or) kinetic energy of the irrigation water. the irrigation water.

…………PumpsPumpsPumps are used in irrigation systems to impart a Pumps are used in irrigation systems to impart a head to the water so it may be distributed to head to the water so it may be distributed to

different locations on the farm and used different locations on the farm and used effectively in application systems.effectively in application systems.

The key requirement in pump selection and The key requirement in pump selection and design of pump systems for typical irrigation design of pump systems for typical irrigation

installations is that there is a correspondence installations is that there is a correspondence between the between the requirements of the irrigation requirements of the irrigation

system and the maximum operating efficiency of system and the maximum operating efficiency of the pump.the pump.

Requirements of irrigationRequirements of irrigation system are:system are:

- flow rates- flow rates

- pressure out put necessary to operate the - pressure out put necessary to operate the systemsystem..

Principles of Water liftingPrinciples of Water lifting

1.1. Direct lift (Direct lift devices)Direct lift (Direct lift devices)

physically lifting water in a containerphysically lifting water in a container2.2. Displacement (Displacement pumps)Displacement (Displacement pumps)

This involves utilizing the fact that water is This involves utilizing the fact that water is (effectively) incompressible and can therefore be (effectively) incompressible and can therefore be 'pushed' or displaced.'pushed' or displaced.

- - Rotary positive displacement pumps, which use gears, Rotary positive displacement pumps, which use gears, vanes, lobes or screws to move, discrete quantities of vanes, lobes or screws to move, discrete quantities of water from the inlet to the outlet of the pump.water from the inlet to the outlet of the pump.

- - Reciprocating positive displacement pumps: piston pumps, Reciprocating positive displacement pumps: piston pumps, plunger pumps, diaphragm pumps.plunger pumps, diaphragm pumps.

3.3. Gravity (Gravity Device)Gravity (Gravity Device)

– – Gravity operated systems, SiphonsGravity operated systems, Siphons

4. Creating a velocity head (velocity 4. Creating a velocity head (velocity pumpspumps

Rotodynamic pumpsRotodynamic pumps: volute centrifugal : volute centrifugal pumps, turbine centrifugal pumps, pumps, turbine centrifugal pumps, regenerative centrifugal pumps.regenerative centrifugal pumps.

Types of pumpsTypes of pumpsPumps used in irrigation systems are available Pumps used in irrigation systems are available in a wide variety of pressure and discharge in a wide variety of pressure and discharge configurations.configurations.

Pressure and discharge are inversely related Pressure and discharge are inversely related in pump design , so pumps which produce in pump design , so pumps which produce high pressure have relatively small discharge high pressure have relatively small discharge and vice versa.and vice versa.

Characteristics of centrifugal , turbine and Characteristics of centrifugal , turbine and propeller pumps is given as below.propeller pumps is given as below.

Impeller design and pump Impeller design and pump characteristics as function of specific characteristics as function of specific

speedspeed

In the above figure,In the above figure, Flow enters the pump from the bottom.Flow enters the pump from the bottom. In centrifugal pumpIn centrifugal pump , energy is imparted to the flow by , energy is imparted to the flow by

the impeller which directs the flow radially outward. the impeller which directs the flow radially outward. Centrifugal pumps have high heads but limited Centrifugal pumps have high heads but limited

discharge.discharge. Francis impellerFrancis impeller – deliver intermediate flow rates but – deliver intermediate flow rates but

there is less energy available to pressurize the fluid.there is less energy available to pressurize the fluid. Propeller typePropeller type system is able to deliver large flow system is able to deliver large flow

volumes but is capable of imparting a very small volumes but is capable of imparting a very small pressure differential to the fluid.pressure differential to the fluid.

Specific Speed - NSpecific Speed - Nss

Means of quantitatively categorizing the Means of quantitatively categorizing the operating characteristics of a pump.operating characteristics of a pump.

0.75H

0.5Q0.2108N

sN

Where: Ns = specific speed , dimensionless

N = Revolutionary speed of pump , rpm

Q = Pump discharge , L /min

H = discharge pressure head , m

Fig. Fig. Impeller shape &maximum efficiency as Impeller shape &maximum efficiency as function of Ns function of Ns

Ns varies from 500 (centrifugal pump) to Ns varies from 500 (centrifugal pump) to

10, 000 (propeller pump).10, 000 (propeller pump).The Ns of a pump is closely related to the The Ns of a pump is closely related to the

maximum operating efficiency of the pump.maximum operating efficiency of the pump.

Operating efficiencyOperating efficiency : ratio of the power imparted : ratio of the power imparted by the impeller to the water compared to the power by the impeller to the water compared to the power supplied to the pump by the motor.supplied to the pump by the motor.

The performance curve indicates that careful The performance curve indicates that careful attention must be given to the discharge attention must be given to the discharge requirements of the pump , which determine the requirements of the pump , which determine the specific speed, so the most suitable pump may be specific speed, so the most suitable pump may be selected.selected.

Classification of pumps

1. Reciprocating positive displacement pumps1. Reciprocating positive displacement pumps • use back and forth movement of mechanical partsuse back and forth movement of mechanical parts Water is for most practical purposes incompressible. Water is for most practical purposes incompressible.

Consequently, if a close fitting piston is drawn through Consequently, if a close fitting piston is drawn through a pipe full of water, it will displace water along the a pipe full of water, it will displace water along the pipe. pipe.

Similarly, raising a piston in a submersed pipe will Similarly, raising a piston in a submersed pipe will draw water up behind it to fill the vacuum which would draw water up behind it to fill the vacuum which would otherwise occurs.otherwise occurs.

Basic relationships between the output or Basic relationships between the output or discharge rate (Q), piston diameter (d), stroke or discharge rate (Q), piston diameter (d), stroke or length of piston travel (S), number of strokes per length of piston travel (S), number of strokes per minute (n), and the volumetric efficiency, which is minute (n), and the volumetric efficiency, which is the percentage of the swept volume that is actually the percentage of the swept volume that is actually pumped per stroke ( η vol )pumped per stroke ( η vol )

Swept area of the piston is A = Swept area of the piston is A =

The swept volume per stroke will be The swept volume per stroke will be V= ASV= AS

The discharge per stroke will be The discharge per stroke will be q = V η q = V η

volvol

The pumping rate (per minute) is The pumping rate (per minute) is Q = nqQ = nq

4

2πd

2. Rotary positive displacement 2. Rotary positive displacement pumpspumps• These are group of devices which utilizes These are group of devices which utilizes

the displacement principle for lifting or the displacement principle for lifting or moving water, but which achieve this by moving water, but which achieve this by using a rotating form of displacer (gears, using a rotating form of displacer (gears, vanes, lobes or screwsvanes, lobes or screws).).

• use gears and vanes to move discrete part use gears and vanes to move discrete part of water.of water.

• These generally produce a continuous, or These generally produce a continuous, or sometimes a slightly pulsed, water output sometimes a slightly pulsed, water output these pumps tend themselves readily to these pumps tend themselves readily to mechanization and mechanization and to high speed operation to high speed operation than reciprocal displacement pumpsthan reciprocal displacement pumps..

3. Rotodynamic (centrifugal) pumps3. Rotodynamic (centrifugal) pumps

• use the centrifugal force of rotating use the centrifugal force of rotating devices (called impellers) to increase devices (called impellers) to increase the kinetic and pressure energy of the kinetic and pressure energy of the water.the water.

• Depends on propelling water using a Depends on propelling water using a spinning impeller of rotor.spinning impeller of rotor.

• There are two main types of rotodynamic There are two main types of rotodynamic pumps (centrifugal pumps), i.e.pumps (centrifugal pumps), i.e. – Volute centrifugal pumpsVolute centrifugal pumps

– Turbine centrifugal pumpsTurbine centrifugal pumps

Reciprocating and rotary pumps are Reciprocating and rotary pumps are called called positive displacement positive displacement pumpspumps, while centrifugal pumps are , while centrifugal pumps are called called variable displacement variable displacement pumpspumps in which the delivery head in which the delivery head varies with the quantity of water varies with the quantity of water pumpedpumped..

Axial flow pumpAxial flow pump

Radial flow (Centrifugal pumps)Radial flow (Centrifugal pumps)

Typical mixed flow pumpTypical mixed flow pump

PUMPING THEORY-CENTRIFUGAL PUMPSPUMPING THEORY-CENTRIFUGAL PUMPS In centrifugal pumps the energy is imparted to the In centrifugal pumps the energy is imparted to the

water by a unit of rotating vanes called an water by a unit of rotating vanes called an impellerimpeller, , which are located in a stationary body called the which are located in a stationary body called the casingcasing..

CASINGCASING Water is pushed into the center or eye of the impeller by Water is pushed into the center or eye of the impeller by

atmospheric or water pressure and set into a rotary atmospheric or water pressure and set into a rotary motion by the impeller.motion by the impeller.

-The rotating movement causes a centrifugal force to act -The rotating movement causes a centrifugal force to act upon the water, which drives the water outward, upon the water, which drives the water outward, between the vanes of the impeller, into the between the vanes of the impeller, into the surrounding casing from where it moves to the pump surrounding casing from where it moves to the pump outlet. outlet.

-Different types of casing: a)-Different types of casing: a)Single voluteSingle volute, (b) , (b) Double Double volutevolute, and (c). , and (c). Diffuser turbine casingDiffuser turbine casing..

IMPELLERSIMPELLERS Impellers can be classified according to the direction Impellers can be classified according to the direction

of flow through the impeller in relation to the axis of of flow through the impeller in relation to the axis of rotation as (a) rotation as (a) radialradial, (b) , (b) axialaxial or (c) or (c) mixed flowmixed flow..

Where high flows at low heads are required (which is Where high flows at low heads are required (which is common with irrigation pumps), the most efficient common with irrigation pumps), the most efficient impeller is an axial flow one.impeller is an axial flow one.

Impellers can also be classified according to their Impellers can also be classified according to their design into design into (a) open (a) open (consist only vanes attached to (consist only vanes attached to the hub with out shroud/side-wall), the hub with out shroud/side-wall), (b) semi-open (b) semi-open (have one shroud) and (have one shroud) and (c) enclosed (c) enclosed (have shrouds (have shrouds (sidewalls) enclosing the waterways between vanes) (sidewalls) enclosing the waterways between vanes) impellers as shown in figure. impellers as shown in figure.

ImpellersImpellers

CENTRIFUGAL PUMP PERFORMANCECENTRIFUGAL PUMP PERFORMANCE Pumping capacity, pumping head, power, efficiency Pumping capacity, pumping head, power, efficiency

and net positive suctionand net positive suction head are the main head are the main parameters, which describe the performance of a parameters, which describe the performance of a pumppump..

1.Pump capacity:1.Pump capacity:

The capacity of a pump is the volume of water (Q) which 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 the pump can deliver per unit of time, e.g. in litters per second (lt/s) or cubic meters per hour.second (lt/s) or cubic meters per hour.

2. Pumping Head2. Pumping Head

The actual pumping head imposed on a pump, gross The actual pumping head imposed on a pump, gross working head, will be somewhat greater than the working head, will be somewhat greater than the actual vertical distance, or static head, water has to be actual vertical distance, or static head, water has to be raised.raised.

The pumping head (H) is the The pumping head (H) is the net work donenet work done on a unit on a unit of water by the pump. It is expressed by the of water by the pump. It is expressed by the Bernoulli’s equation.Bernoulli’s equation.

H = (p/(H = (p/(g) + Vg) + V22/(2g) + Z)/(2g) + Z)dd - (p/(pg) + V - (p/(pg) + V22/(2g) + Z)/(2g) + Z)ss

P = Water pressure in (kpa or meters water column)P = Water pressure in (kpa or meters water column)

= density of the fluid in (kg/m= density of the fluid in (kg/m33))

g = acceleration due to gravity in (m/Sg = acceleration due to gravity in (m/S22))

V = Water velocity in (m/s)V = Water velocity in (m/s)

Z = Elevation head in meters relative to a reference level or Z = Elevation head in meters relative to a reference level or datum.datum.

g = g = =specific weight of the fluid (kN/m =specific weight of the fluid (kN/m33))

PowerPower

The amount of energy (in joule) applied per The amount of energy (in joule) applied per unit of time (seconds) is the power imparted to unit of time (seconds) is the power imparted to the water in joule/ second = Wattthe water in joule/ second = Watt..

PPhydrhydr = = g H Q = g H Q =

PPhydrhydr == hydraulichydraulic or water power in Watt.or water power in Watt.

QQ = pumped volume in m = pumped volume in m33/s./s. Pumping at a rate of 180mPumping at a rate of 180m33/ h at a head of / h at a head of

120 meters require:120 meters require:PPhydrhydr = 1000 x 9.81 x 120 x 180/3600 = 4, 905 watt = 4.9 = 1000 x 9.81 x 120 x 180/3600 = 4, 905 watt = 4.9

kwkw

HQ

Pump EfficiencyPump Efficiency

The actual power and energy needs are always greaterThe actual power and energy needs are always greater

than the hydraulic energy neededthan the hydraulic energy needed

Therefore, the pump efficiency (Therefore, the pump efficiency (pumppump) is the percent of ) is the percent of

power input by a motor (in kw) to the pump shaft (the power input by a motor (in kw) to the pump shaft (the so-called brake power) which is transferred to the so-called brake power) which is transferred to the water:water:

hydrhydr = (P = (Phydrhydr / P / Pmotormotor)x 100)x 100

hydrhydr = pump efficiency = pump efficiency

PPhydrhydr = water power (kw, hp) = water power (kw, hp)

P Pmotormotor = break power (kw, hp) = break power (kw, hp)

Pump Power RequirementsPump Power Requirements

The power added to water as it moves through a The power added to water as it moves through a pump can be calculated with the following formula:pump can be calculated with the following formula:

WHP = WHP = Q x TDHQ x TDH

39603960

where: WHP = Water Horse Power where: WHP = Water Horse Power

Q = Flow rate in gallons per minute (GPM) Q = Flow rate in gallons per minute (GPM)

TDH = Total Dynamic Head (feet) TDH = Total Dynamic Head (feet)

Break Horse powerBreak Horse power

BHP = WHPBHP = WHP

Pump Eff. x Drive Eff. Pump Eff. x Drive Eff.

BHP --BHP -- Brake Horsepower (continuous horsepower rating of the Brake Horsepower (continuous horsepower rating of the power unit). power unit).

Pump Eff. --Pump Eff. -- Efficiency of the pump usually read from a pump Efficiency of the pump usually read from a pump curve and having a value between 0 and 1. curve and having a value between 0 and 1.

Drive Eff. --Drive Eff. -- Efficiency of the drive unit between the power source Efficiency of the drive unit between the power source and the pump. For direct connection this value is 1, for right and the pump. For direct connection this value is 1, for right angle drives the value is 0.95 and for belt drives it canangle drives the value is 0.95 and for belt drives it can

vary from 0.7 to 0.85. vary from 0.7 to 0.85.

Net Positive Suction Head- NPSHNet Positive Suction Head- NPSH The net positive section head (NPSH) is the amount The net positive section head (NPSH) is the amount

of energy required to prevent the formation of vapor of energy required to prevent the formation of vapor filled cavities within the eye of the single and fires filled cavities within the eye of the single and fires stage impellers.stage impellers.

This cavities which form when pressure within the This cavities which form when pressure within the eye drop below the vapor pressure of water collapse eye drop below the vapor pressure of water collapse within higher-pressure areas of the pump. within higher-pressure areas of the pump.

The formation and subsequent collapse of these The formation and subsequent collapse of these vapor filled cavities is called cavitation. vapor filled cavities is called cavitation.

When cavities collapse occur violently at interior When cavities collapse occur violently at interior surfaces of the pump they produce ring-shaped surfaces of the pump they produce ring-shaped indentations in the surface called pits. Continued indentations in the surface called pits. Continued pitting severely damage pumps, and must be pitting severely damage pumps, and must be avoidedavoided

The NPSH required to prevent cavitation is a The NPSH required to prevent cavitation is a function of pump design and is usually determined function of pump design and is usually determined experimentally for each pump.experimentally for each pump.

Cavitation is prevented when heads (available Cavitation is prevented when heads (available NPSH) within the eye of single and first impeller NPSH) within the eye of single and first impeller exceeds the NPSH, value published by the exceeds the NPSH, value published by the manufacturers.manufacturers.

The available NPSH is a function of the The available NPSH is a function of the atmospheric pressure, vapor pressure, atmospheric pressure, vapor pressure, friction loss, suction head and should always friction loss, suction head and should always exceed the NPSH specified by the pump exceed the NPSH specified by the pump manufacturer with at least 0.5 to 1.0 meters manufacturer with at least 0.5 to 1.0 meters of head. of head.

NPSH = Ha - Hs - HNPSH = Ha - Hs - Hff –H –Hvpvp

Ha = atmospheric pressure on the surface of the water Ha = atmospheric pressure on the surface of the water (in m)(in m)

Hs = elevation of the water above or below the impeller Hs = elevation of the water above or below the impeller eye while pumping (in m) (if the level is above the eye, eye while pumping (in m) (if the level is above the eye, Hs is positive, if the level is below the eye, Hs is Hs is positive, if the level is below the eye, Hs is negative)negative)

HHff = friction-head losses in the suction piping (in m) = friction-head losses in the suction piping (in m)HHvpvp = Vapor pressure of the water at the pumping = Vapor pressure of the water at the pumping

temperature (in m).temperature (in m). The vapor pockets, which form when pressures The vapor pockets, which form when pressures

within the eye of the impeller drop below the within the eye of the impeller drop below the vapor pressure of the water, subsequently vapor pressure of the water, subsequently collapse violently within the high pressure collapse violently within the high pressure areas of the pump.areas of the pump.

This collapse is called This collapse is called cavitationcavitation and can and can cause severe damage to the pump. cause severe damage to the pump. Operate the Operate the pump with in its design capacity.pump with in its design capacity.

PERFORMANCE CURVESPERFORMANCE CURVES

Head versus pump capacity.Head versus pump capacity. Efficiency versus pump Efficiency versus pump

capacity.capacity. Brake power versus pump Brake power versus pump

capacity.capacity. NPSH versus pump capacity.NPSH versus pump capacity.

AFFINITY LAWSAFFINITY LAWS

The performance of a pump varies with the speed The performance of a pump varies with the speed at which the impeller rotates. at which the impeller rotates. TheoreticallyTheoretically, , varying the pump speed will result in changes in varying the pump speed will result in changes in flow rate, TDH and BHP according to the following flow rate, TDH and BHP according to the following formulas:formulas:

For a constant DiameterFor a constant Diameter

QQ22= Q= Q11 x (N x (N22/N/N11))

HH22 = H = H11 x (N x (N22/N/N11) ) 2 2

BPBP22= BP= BP11 x (N x (N22/N/N11) ) 33

NPSHNPSH22 = NPSH = NPSH11 x (N x (N22/N/N11) ) 22

…………Affinity LawsAffinity Laws

For constant N ( Rotation per minute)For constant N ( Rotation per minute)

QQ22 = Q = Q11 x (D x (D22/D/D11))

HH22 = H = H11 x (D x (D22/D/D11) ) 22

BPBP22 = BP = BP11 x (D x (D22/D/D11) ) 33

NPSHNPSH22 = NPSH = NPSH11 x (D x (D22/D/D11))22

wherewhere

Q = dischargeQ = discharge

N=number of Revolution per minuteN=number of Revolution per minute

BP = Break powerBP = Break power

NPSH = Net positive suction headNPSH = Net positive suction head

D = diameterD = diameter

H = Available headH = Available head

Pump performance curvesPump performance curves

Q

H

Typical Pump performance curveTypical Pump performance curve

Pump operation pointPump operation point A centrifugal pump operates at A centrifugal pump operates at

combinations of head and discharge combinations of head and discharge according to its H-Q characteristic according to its H-Q characteristic performance curve. The particular performance curve. The particular combination of H-Q at which a pump is combination of H-Q at which a pump is operating is the pump’s operating point. operating is the pump’s operating point. Power requirement, efficiency and NPSH for Power requirement, efficiency and NPSH for the pump can be determined once the the pump can be determined once the operating point is known.operating point is known.

The specific operating point depends on the The specific operating point depends on the head and water volume requirements of the head and water volume requirements of the irrigation system. A system curve irrigation system. A system curve describes the H–Q performance of the describes the H–Q performance of the irrigation system. irrigation system.

The system curve is then combined with the The system curve is then combined with the H-Q characteristic curve of the pump to H-Q characteristic curve of the pump to determine the operating point.determine the operating point.

…….Pump operation point.Pump operation point

Operating points can be altered by Operating points can be altered by changing either the changing either the H-Q H-Q curve for the curve for the pump or for irrigation system. Pump can pump or for irrigation system. Pump can be altered by changing the pump speed or be altered by changing the pump speed or the impeller diameter (see the Affinity the impeller diameter (see the Affinity Laws). Laws).

Shifting pump operation pointShifting pump operation point

Pump curve for 2000rpm

Pump curve for 1800 rpm

Q

H

Pump operation point

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 The system curve is constructed by calculating the system head Hs required by the irrigation to deliver varying head Hs required by the irrigation to deliver varying volumes of water per unit of time.volumes of water per unit of time.

The system head Hs is calculated with the formulaThe system head Hs is calculated with the formula

Hs = SHs = SLL+ D+ DLL+ D+ DDD+ H+ H11 + M + M11 +H +HOO + V + VHH

Where:Where:

HHSS = System head (m) = System head (m)

SSLL = Suction lift from static water level (m) = Suction lift from static water level (m)

DDLL = discharge lift from pump to highest discharge point = discharge lift from pump to highest discharge point

(m)(m)

DDDD = draw down in water source (m) = draw down in water source (m)

HH11 = head loss in delivery pipes (m) = head loss in delivery pipes (m)

MM11 = minor losses in fittings (m) = minor losses in fittings (m)

HHoo = operating head (m) = operating head (m)

VVHH = velocity head (m) = velocity head (m)

Total Dynamic HeadTotal Dynamic Head The total dynamic head of a pump is the sum of the The total dynamic head of a pump is the sum of the

total static head, the pressure head, the friction head, total static head, the pressure head, the friction head, and the velocity head.and the velocity head.

TDH =Z +HTDH =Z +Hss + h + hv v + h+ hff

Total Static HeadTotal Static Head

The total static head is the total vertical distance the pump must The total static head is the total vertical distance the pump must lift the water. When pumping from a well, it would be the lift the water. When pumping from a well, it would be the distance from the pumping water level in the well to the ground distance from the pumping water level in the well to the ground surface plus the vertical distance the water is lifted from the surface plus the vertical distance the water is lifted from the ground surface to the discharge point. When pumping from an ground surface to the discharge point. When pumping from an open water surface it would be the total vertical distance from open water surface it would be the total vertical distance from

the water surface to the discharge pointthe water surface to the discharge point. .

Static HeadStatic Head

Water Horse Power (WHP)Water Horse Power (WHP) WHP = Q H WHP = Q H WHP = the energy pump produces to move the waterWHP = the energy pump produces to move the water

BHP = Input power to the pump given by the motorBHP = Input power to the pump given by the motor

= out put of the motor= out put of the motor

Input power for the motor is from electricity.Input power for the motor is from electricity.

P = P = Q H SQ H Sgg

4634 E4634 E

γ

Where:P = power , metric horse powerQ = Pump discharge, L/minH= Discharge pressure head, mSg =specific gravity of fluid, dimensionlessE = pump efficiency , fraction

P = P = Q H SgQ H Sg

278.04 E 278.04 E

P = P = Q H SgQ H Sg

0.102 E0.102 E

Where Q = m3/hr

Where P = power , KW Q = discharge , m3/s

P = Q x TDH Sg 3960 E

Where P = power, brake horse power (bhp)

Q = pump discharge , (gpm)

TDH or H = Discharge pressure head , ft

Water Horse Power (WHP)Water Horse Power (WHP)

WHP = Q H WHP = Q H

WHP = the energy pump produces to move the waterWHP = the energy pump produces to move the water

BHP = Input power to the pump given by the motorBHP = Input power to the pump given by the motor

= out put of the motor= out put of the motor

Input power for the motor is from electricity.Input power for the motor is from electricity.

Motor Pump WHP input BHP

Em Ep

EPP

Pump efficiencyPump efficiency

EEp p = = WHPWHP / / BHPBHP

EEmm = BHP/ input = BHP/ input

EEPPPP = = WHP/ input = EWHP/ input = Epp . E . Emm

Where EWhere Emm = Efficiency of motor = Efficiency of motor

EEpp = efficiency of pump = efficiency of pump

EEPP PP = Efficiency of pumping plant = Efficiency of pumping plant

Combination of pumpsCombination of pumpsPumps in parallelPumps in parallel

- - To provide more Q and not more headTo provide more Q and not more head

Q = QQ = Q11 + Q + Q2 2 + Q+ Q33

P2 P3P1

Q

River

Q1 Q3Q2

Pumps in seriesPumps in series

To Create more head. This is so by To Create more head. This is so by using submersible pumpsusing submersible pumps..

P2

P3

P1

Q

In Submersible pump a number of impellers are connected in series

Water Source

Q

Q

Q H = H1 + H2+ H3

NPSHNPSH

The head which let water flow through the The head which let water flow through the suction pipe in to the pump.suction pipe in to the pump.

NPSH NPSH required required - - is the head required at the inlet of is the head required at the inlet of the impeller to insure that the liquid will not boil the impeller to insure that the liquid will not boil or form vapour pockets which will result in or form vapour pockets which will result in cavitation.cavitation.

NPSHNPSHavial.avial. = P = Patm atm - Z- Zss- P- PV V – h– hfsfs

The height to which the pump has to be raised should The height to which the pump has to be raised should be low in order not to cause cavitation.be low in order not to cause cavitation.

To Estimate Zs , assume NPSHTo Estimate Zs , assume NPSHavailavail. = NPSH. = NPSHreqreq..

atm. Pressure - static suction head - vapor pr/ head - friction head loss

Pump SelectionPump SelectionProcess of choosing the most suitable Process of choosing the most suitable

pump for the irrigation system.pump for the irrigation system. It involves the specification of the It involves the specification of the

discharge and pressure requirements of the discharge and pressure requirements of the irrigation systemirrigation system, selecting the , selecting the required required

pumping methodpumping method and identifying the and identifying the different pumpsdifferent pumps (within the chosen (within the chosen

method), which can meet the requirements method), which can meet the requirements of the irrigation system.of the irrigation system.

financial Criteriafinancial Criteria

management Criteriamanagement Criteria..

PEREFORMANCE REQUIREMENTSPEREFORMANCE REQUIREMENTS The discharge and head requirements of the The discharge and head requirements of the

irrigation system are a function of :irrigation system are a function of : CWR in the different stages of growth, CWR in the different stages of growth, The size of the land to be irrigated,The size of the land to be irrigated, The method of irrigation The method of irrigation The system layoutThe system layout

Discharge –Head requirement of the irrigation Discharge –Head requirement of the irrigation system must agree with Discharge head system must agree with Discharge head requirement of the operating system (pump)requirement of the operating system (pump)

Identifying suitable pumpsIdentifying suitable pumps The horizontally installed The horizontally installed volute suction pumpvolute suction pump and the and the

vertical diffuser (turbinevertical diffuser (turbine) pumps are the most suitable ) pumps are the most suitable and most commonly used pumps with irrigation and most commonly used pumps with irrigation systems. systems.

Horizontal volute suctionHorizontal volute suction pumps are usually cheaper pumps are usually cheaper and easier to install than vertical pumps.and easier to install than vertical pumps.

Vertical turbine pumpsVertical turbine pumps, which are , which are positioned below the positioned below the water levelwater level, are used in deep wells or when the water , are used in deep wells or when the water level is too far from a suitable surface pump positions level is too far from a suitable surface pump positions to accommodate the NPSH requirements.to accommodate the NPSH requirements.

Vertical pumps are sometimes also used to eliminate Vertical pumps are sometimes also used to eliminate the need for priming of horizontal pumpsthe need for priming of horizontal pumps

The pump’s required NPSH is given by the The pump’s required NPSH is given by the pump characteristic curves provided by the pump characteristic curves provided by the manufacturer.manufacturer.

The available NPSH must then be determined The available NPSH must then be determined under local conditions and compared to the under local conditions and compared to the required NPSH, whereby the required NPSH, whereby the available should available should be at least 0.5 to 1.0be at least 0.5 to 1.0 mm more than the more than the required required NPSH.NPSH.

What if the available NPSH is less than the What if the available NPSH is less than the required NPSH in Vertical Turbine pumps?required NPSH in Vertical Turbine pumps?

Increase the depth of submergence….Increase the depth of submergence….

Consult manufacturer’s criteria (pump Consult manufacturer’s criteria (pump characteristic curve) to select suitable pump.characteristic curve) to select suitable pump.

Selection Criteria must consider: Selection Criteria must consider: Financial constraints – EconomyFinancial constraints – Economy Tangible benefits – not quantified in monetary Tangible benefits – not quantified in monetary

terms reliability ,availability of spare parts , terms reliability ,availability of spare parts , maintenance skillsmaintenance skills

Proper analysis of investment (fixed costs) & Proper analysis of investment (fixed costs) & operational costs.operational costs.

The cheapest system is not The cheapest system is not always the best, since low always the best, since low investment costs often result in investment costs often result in high running costshigh running costs !!!!!!

Investment in a pumping system should not be Investment in a pumping system should not be considered as one-off cash expenditure.considered as one-off cash expenditure.

The current value of the money compared to its The current value of the money compared to its future value, taking into account interest rates future value, taking into account interest rates (a), inflation (i) and the annual repayment of the (a), inflation (i) and the annual repayment of the loan. Spread out over the life cycle (n) of the loan. Spread out over the life cycle (n) of the pumping system (pump and motor)- pumping system (pump and motor)- annulization.annulization.

Step-by-step procedure of costing irrigation pumpsStep-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 costsOperating costs Energy, maintenance and repair costEnergy, maintenance and repair cost are generally are generally

considered recurrent operating or running costs.considered recurrent operating or running costs. The energy costs are a function of the load on the The energy costs are a function of the load on the

pump and the operating time per year.pump and the operating time per year. A pump will not necessarily operate under the same A pump will not necessarily operate under the same

head and discharge requirements during the whole head and discharge requirements during the whole year.year.

In this case the hydraulic power requirement and In this case the hydraulic power requirement and efficiency of the pump will differ and therefore the efficiency of the pump will differ and therefore the brake or motor power also vary. brake or motor power also vary.

The respective The respective motor power requirementmotor power requirement times times the the respective operating hours per yearrespective operating hours per year will will suggest the suggest the kwh /yearkwh /year

Annual maintenance and repair costs may also be Annual maintenance and repair costs may also be budgeted as a percentage of the original investment budgeted as a percentage of the original investment cost.cost.

OTHER COSTSOTHER COSTS

distribution system, distribution system,

the intake or borehole, the intake or borehole,

pump house, pump house,

personnel costs, etcpersonnel costs, etc

-AVAILABILITY OF TECHNOLOGY AND SPARES-AVAILABILITY OF TECHNOLOGY AND SPARES

-OPERATIONAL CONVENIENCE- skilled man-OPERATIONAL CONVENIENCE- skilled man

-Reliability-Reliability

Must be included in the cost estimation

Pump installationPump installation

Pump housePump house

When a pump is selected one of the criteria When a pump is selected one of the criteria influencing the selection process will be the influencing the selection process will be the available space and intended position of the available space and intended position of the pump.pump.

will the pump be suction pump, mounted at the will the pump be suction pump, mounted at the surface?surface?

will it be a turbine pump with only the motor at the will it be a turbine pump with only the motor at the surface? surface?

will the motor and pump be submerged below the will the motor and pump be submerged below the water? water?

In the case of surface pumps, will it be a mobile or In the case of surface pumps, will it be a mobile or a permanent installation?a permanent installation?

Guidelines for permanent pump Guidelines for permanent pump installationsinstallations

The place where the pump will be located will The place where the pump will be located will need to be easily accessible;need to be easily accessible;

In most cases it will be an advantage to have In most cases it will be an advantage to have the pump, motor and /or switchboard located the pump, motor and /or switchboard located in a pump house for the simple sake of in a pump house for the simple sake of protection (weather/theft/destruction);protection (weather/theft/destruction);

The pump house will need to be large enough The pump house will need to be large enough for installation, maintenance and repair for installation, maintenance and repair activities;activities;

For the bigger equipment there should be the For the bigger equipment there should be the possibility of lifting equipment being installed possibility of lifting equipment being installed to move the pump;to move the pump;

Drainage facilities should be provided for spill Drainage facilities should be provided for spill water when the pump is being dismantled;water when the pump is being dismantled;

Special needs to be given to lighting and Special needs to be given to lighting and ventilation and – in the case of below zero ventilation and – in the case of below zero temperatures-heatingtemperatures-heating;;

Pump installations near inhabited areas will Pump installations near inhabited areas will require a form of noise protection;require a form of noise protection;

InstallationInstallation Mobile pump installations may be trailer mounted or Mobile pump installations may be trailer mounted or

connected to, for example, a tractor. connected to, for example, a tractor.

permanent pumping installations.permanent pumping installations. Horizontal pumps are usually constructed with their Horizontal pumps are usually constructed with their

motor on one steel base plate or framemotor on one steel base plate or frame . . With permanent installations the pump and motor will With permanent installations the pump and motor will

be positioned on a reinforced concrete slab.be positioned on a reinforced concrete slab. The slab should be constructed in such a manner that:The slab should be constructed in such a manner that: it is large enough to fit the whole pump& motorit is large enough to fit the whole pump& motor it is strong enough to carry the weight of the pump& it is strong enough to carry the weight of the pump&

motor.motor. during operation no vibration occursduring operation no vibration occurs

To avoid motor and pump vibrations to be To avoid motor and pump vibrations to be transmitted to the floor of the pump house, a transmitted to the floor of the pump house, a 50mm thick cork or rubber layer can be 50mm thick cork or rubber layer can be included in the slab. included in the slab.

ALIGNMENTALIGNMENT It is essential that motor and pump are aligned It is essential that motor and pump are aligned

precisely. If this is not the case additional forces precisely. If this is not the case additional forces will come out in the bearings of both and cause will come out in the bearings of both and cause overheating and eventually the system will overheating and eventually the system will brake down.brake down.

Proper alignment is also essential with the use Proper alignment is also essential with the use of vertical turbine pumps to avoid damage to of vertical turbine pumps to avoid damage to the bearings of the pump and motor.the bearings of the pump and motor.

Consolidation or settlement of the soil can also cause Consolidation or settlement of the soil can also cause misalignment after a pump has been in installed. misalignment after a pump has been in installed. Regular checking of pumping unit and pipeline Regular checking of pumping unit and pipeline connections should be carried out to avoid potential connections should be carried out to avoid potential damage.damage.

ELECTRICAL CONNECTIONSELECTRICAL CONNECTIONS With electrical motor units extreme care should be With electrical motor units extreme care should be

taken to properly protect and insulate the electrical taken to properly protect and insulate the electrical cables, connections and switches. The unit should cables, connections and switches. The unit should be properly grounded. be properly grounded.

PIPE CONNECTIONSPIPE CONNECTIONS The correct installation and connection of the The correct installation and connection of the

suction and delivery pipes to the pump unit is suction and delivery pipes to the pump unit is equally important.equally important.

Many pump failures can be attributed to Many pump failures can be attributed to incorrect or imprecise suction conditions.incorrect or imprecise suction conditions.

Some guidelines are:Some guidelines are: the suction line should be as short as possible;the suction line should be as short as possible; the suction line should rise to the pump to the suction line should rise to the pump to

avoid air pockets. If unavoidable, filling/air avoid air pockets. If unavoidable, filling/air valve has to be fitted (see figure 6.4);valve has to be fitted (see figure 6.4);

the suction line should have as few bends as the suction line should have as few bends as possible and bends should have a wide radiuspossible and bends should have a wide radius

suction lines should have a side diameter;suction lines should have a side diameter; contractions should be eccentric to avoid air contractions should be eccentric to avoid air

pockets pockets

Suction lines should have absolutely no Suction lines should have absolutely no leakages;leakages;

Non-self priming pumps should have a wide-Non-self priming pumps should have a wide-diameter foot valve at the Inlet side of the diameter foot valve at the Inlet side of the suction pipe;suction pipe;

A low-resistance restrainers should be fitted to A low-resistance restrainers should be fitted to avoid contamination from entering the pump, avoid contamination from entering the pump, while avoiding excessive friction loss;while avoiding excessive friction loss;

Adequate submergence below the lowest Adequate submergence below the lowest water level to avoid the intake of air at the water level to avoid the intake of air at the inlet;inlet;

DELIVERY PIPEDELIVERY PIPE Regulations for the delivery system are less Regulations for the delivery system are less

strict than for the suction line.strict than for the suction line. Non –return valve should be fitted after the Non –return valve should be fitted after the

pump if the delivery line remains under pump if the delivery line remains under pressure after the pump is turned off;pressure after the pump is turned off;

A control valve can be fitted:A control valve can be fitted:– inspection and repair;inspection and repair;– pump to be started under a no-flow conditions;pump to be started under a no-flow conditions;– to (occasionally) regulate the flow in the delivery to (occasionally) regulate the flow in the delivery

system. Note that this should never be done by a system. Note that this should never be done by a valve in the suction line! valve in the suction line!

With positive displacement pumps it is essential With positive displacement pumps it is essential to include a safety valve between the pump and to include a safety valve between the pump and the control valve.the control valve.

WATER HAMMERWATER HAMMER When water is flowing through a distribution When water is flowing through a distribution

system a sudden change in the flow velocity system a sudden change in the flow velocity can cause extreme pressure changes.can cause extreme pressure changes.

A change in the flow can be the result of A change in the flow can be the result of closing a valve or the turning off of the pump.closing a valve or the turning off of the pump.

This pressure is transmitted throughout the This pressure is transmitted throughout the pipeline and reverses direction as soon as it pipeline and reverses direction as soon as it reaches the end of the line.reaches the end of the line.

At the opposite end a corresponding negative At the opposite end a corresponding negative pressure will occur. Both the positive and pressure will occur. Both the positive and negative pressure can cause severe damage negative pressure can cause severe damage to the pipelines.to the pipelines.

The water hammer can be reduced as follows:The water hammer can be reduced as follows:

1. by reducing the normal flow velocity through 1. by reducing the normal flow velocity through the system by choosing larger diameter pipes;the system by choosing larger diameter pipes;

2. Reducing the speed with which the flow in the 2. Reducing the speed with which the flow in the system can be changed by:system can be changed by:

=>using slow control valves=>using slow control valves

=>using air pressure tanks –as buffer=>using air pressure tanks –as buffer

MOTOR MOTOR When pump and motors are purchased separately When pump and motors are purchased separately

it is important to follow the manufacturer’s it is important to follow the manufacturer’s instructions for motor installation carefully.instructions for motor installation carefully.

Care should be taken that the capacity of the Care should be taken that the capacity of the supply is sufficient to run the motor and that the supply is sufficient to run the motor and that the wiring used is according to the specifications of the wiring used is according to the specifications of the manufacturermanufacturer..

Before starting the motor the lubrication of pump Before starting the motor the lubrication of pump and motor should be checked against the and motor should be checked against the manufacturer’s instructions.manufacturer’s instructions.

After this the rotation direction of the motor must After this the rotation direction of the motor must be checked.be checked.

With many pumps only one direction of rotation is With many pumps only one direction of rotation is permissible because otherwise bearings, seals and permissible because otherwise bearings, seals and couplings may become loosened and disconnected.couplings may become loosened and disconnected.

PRIMINGPRIMING With non-self-priming pumps the pump and the With non-self-priming pumps the pump and the

whole suction line have to be filled with water before whole suction line have to be filled with water before the pump can be functional. In places where air the pump can be functional. In places where air accumulates in the system the air should be accumulates in the system the air should be released.released.

If the level is higher than the pump, the opening of If the level is higher than the pump, the opening of the air valve will be sufficient to fill the suction line the air valve will be sufficient to fill the suction line and pump with water;and pump with water;

When there is no gravity flow to the pump three other When there is no gravity flow to the pump three other methods are commonly used:methods are commonly used:

AA. from an outside source with a funnel;. from an outside source with a funnel; B. via a return line with check valve from the delivery B. via a return line with check valve from the delivery

systemsystem

C. With a vacuum pumpC. With a vacuum pump With self-priming pumps generally only the With self-priming pumps generally only the

pump has to be filled with water. In pump has to be filled with water. In exceptional cases with long suction lines exceptional cases with long suction lines or high suction lifts extra water may need or high suction lifts extra water may need to be added. This will be specified in the to be added. This will be specified in the manufacturer’s instructions.manufacturer’s instructions.

Intake structuresIntake structures