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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.

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pumps

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.

pumps1

……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 irrigationsystem are:

- flow rates

- pressure out put necessary to operate the system.

principles of water lifting
Principles of Water lifting
  • Direct lift (Direct lift devices)

physically lifting water in a container

  • 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.

slide4
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
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.

in the above figure
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 n s
Specific Speed - Ns
  • Means of quantitatively categorizing the operating characteristics of a pump.

Where: Ns = specific speed , dimensionless

N = Revolutionary speed of pump , rpm

Q = Pump discharge , L /min

H = discharge pressure head , m

slide10
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.
slide12
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 )
slide13
Swept area of the piston is A =

The swept volume per stroke will be V= AS

The discharge per stroke will be q = V η vol

The pumping rate (per minute) is Q = nq

2 rotary positive displacement pumps
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
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
slide16
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.
pumping theory centrifugal pumps
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
  • 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.
centrifugal pump performance
CENTRIFUGAL PUMP PERFORMANCE
  • Pumping capacity, pumping head, power, efficiency and net positive suctionhead 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.

slide25
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
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 =

Phydr=hydraulicor 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
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
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
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
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
slide31
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.
slide32
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
PERFORMANCE CURVES
  • Head versus pump capacity.
  • Efficiency versus pump capacity.
  • Brake power versus pump capacity.
  • NPSH versus pump capacity.
affinity laws
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 laws1
……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

slide36
where

Q = discharge

N=number of Revolution per minute

BP = Break power

NPSH = Net positive suction head

D = diameter

H = Available head

slide39
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 H-Q characteristic curve of the pump to determine the operating point.
pump operation 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

H

Pump curve for 1800 rpm

Pump operation point

Q

Shifting 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.

slide42
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
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.
water horse power whp
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.

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

slide47

Where Q = m3/hr

P = Q H Sg

278.04 E

P = Q H Sg

0.102 E

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 whp1

input

BHP

Motor

Pump

WHP

Em

Ep

EPP

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.

pump efficiency1
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
Combination of pumps
  • Pumps in parallel

- To provide more Q and not more head

Q = Q1 + Q2 + Q3

Q

P2

P3

P1

Q2

Q1

Q3

River

pumps in series
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

slide52
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

  • 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.

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

pump selection

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.

slide54
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)
slide55
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
slide56
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 1.0m 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.
slide57
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!!!
slide58
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

Step-by-step procedure of costing irrigation pumps
slide60
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
slide61
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

slide62
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
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;
slide64
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;
slide65
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
slide66
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.
slide67
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.
slide68
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
slide69
Suction lines should have absolutely no leakages;
  • Non-self priming pumps should have a wide-diameter 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
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!
slide71
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.
slide72
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

slide73
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.
slide74
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:
slide75
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