Pumping PlantsPumping Plants

Types of PumpsTypes of Pumps• Positive displacement pumps

– Rotary (gear, screw, etc.) – Reciprocating (piston, diaphragm, etc.)– Used as injection and sprayer pumps,

but not for irrigation water

• Centrifugal pumps– Rotating impeller converts mechanical

energy into hydraulic energy (show examples and transparency)

Rotating Impeller Converts Mechanical Rotating Impeller Converts Mechanical Energy to Hydraulic EnergyEnergy to Hydraulic Energy

Centrifugal Pump ImpellersCentrifugal Pump Impellers

Enclosed Impeller Semi-Open Impeller

Centrifugal PumpsCentrifugal Pumps

• Horizontal– Drive shaft is horizontal– Often used when pumping from a

surface source (pond, lake, stream, etc.), Or for boosting the pressure in an irrigation pipeline (booster pump)

– Usually sold as completely assembled units

Typical Horizontal Centrifugal Pump InstallationTypical Horizontal Centrifugal Pump Installation

Horizontal Horizontal Centrifugal PumpsCentrifugal Pumps

Centrifugal Pumps, Contd...Centrifugal Pumps, Contd...

• Vertical Turbine– drive shaft is vertical– used when pumping from a well – normally custom built from

components (with multiple stages)– submersible: electric motor below

the lowest stage

Vertical Turbine PumpVertical Turbine Pump

Single-Stage Vertical Turbine PumpSingle-Stage Vertical Turbine Pump

Water Flow Path Water Flow Path Through a One-Stage Through a One-Stage Vertical Turbine PumpVertical Turbine Pump

Two-Stage Vertical Turbine PumpTwo-Stage Vertical Turbine Pump

Water Flow Path Water Flow Path Through a Two-Stage Through a Two-Stage Vertical Turbine PumpVertical Turbine Pump

Gearhead for Gearhead for engine driveengine drive

Holloshaft electric Holloshaft electric motormotor

(Discharge Heads)

Submersible Water PumpsSubmersible Water Pumps

- Same as vertical turbine Same as vertical turbine pump designpump design

- Driven from below by Driven from below by electric motorelectric motor

- Good for deep wellsGood for deep wells

- High efficiencyHigh efficiency

- Wells as small as 4” diameterWells as small as 4” diameter

Head Capacity Curve (Fig. 8.6)Head Capacity Curve (Fig. 8.6)

Pump CharacteristicsPump Characteristics

• Head vs. discharge– discharge (or capacity): volume of

water pumped per unit of time (gpm)– head (or total head or total dynamic

head):– energy added to the water by the

pump– units of feet (energy per unit weight of

water

Pump Characteristics Cont’d…Pump Characteristics Cont’d…

• Pump Efficiency vs. Discharge

Power = energy/time; 1 HP = 33,000 ft-lb/min 

- Q in gpm; TDH in ft, whp in horsepower- whp = power added to the water by the

pump

Eoutput power (or energy)

input power (or energy)

water HP

brake HP

whp

bhpp

whp =(Q)(TDH)

3960

Pump Characteristics Contd…Pump Characteristics Contd…• Brake horsepower vs. Discharge

where: Q, (gpm); TDH, (ft); bhp & whp, (HP)

• Combined characteristic curves– Horizontal centrifugal pump – Vertical turbine pump

bhp =whp

E

(Q)(TDH)

(3960)(Ep p

)

Vertical Turbine Pump Performance CurveVertical Turbine Pump Performance Curve

Horizontal Centrifugal Pump Performance CurveHorizontal Centrifugal Pump Performance Curve

Affinity Laws Affinity Laws

• Speed– Law applies to virtually all irrigation pumps

– Ep may be affected a little, but not as predictable

– Ways of changing speeds: pulleys, gear ratios, throttle,

change motor

Q

Q

RPM

RPM

TDH

TDH

RPM

RPM

bhp

bhp

RPM

RPM2

1

2

1

2

1

2

1

2

1

2

1

2 3

Affinity Law ExampleAffinity Law ExampleA pump operating at 1800 RPM delivers 200 gpm at a TDH of 150 feet and requires 10 HP to operate. What will be its Q, TDH and BHP conditions if it is sped up to 2000 RPM?

RPM1=1800 RPM2= 2000 RPM2/RPM1=1.11

Q2/Q1= RPM2/RPM1 Q2= Q1 x RPM2/RPM1 = 200 x 1.11= 222 gpm

TDH2/TDH1=[RPM2/RPM1]2 TDH2 = TDH1 x [RPM2/RPM1]2

TDH2 = 150 x [1.11]2 = 185 feet

BHP2/BHP1 = =[RPM2/RPM1]3 BHP2 = BHP1 x [RPM2/RPM1]3

BHP2 = 10 x [1.11]3 = 13.7 HP

Affinity Laws Contd…Affinity Laws Contd…• Impeller diameter

– Law strictly applies only to horizontal centrifugal pumps, but good approximation for vertical turbine pumps 

• Ep may change a little 

• Diameter is changed by trimming the impeller (law holds up to about 10-20% trim)

3

1

2

1

2

2

1

2

1

2

1

2

1

2

D

D

bhp

bhp

D

D

TDH

TDH

D

D

Q

Q

Pumps in SeriesPumps in Series• Booster pump• Multi-stage turbine pump

•  Q1 = Q2

•  TDHtot = TDH1 + TDH2 (add heads at the same

discharge)

•  bhptot = bhp1 + bhp2

tot

tot

p bhp

TDHQ

E 3960)(

Pumps in Series Cont’d…Pumps in Series Cont’d…

Pumps in ParallelPumps in Parallel

Pumps in Parallel Contd…Pumps in Parallel Contd…

• Qtot = Q1 + Q2 (add discharges at the same

head)

• bhptot = bhp1 + bhp2

E

Q H

bhpp

tot

tot

( )3960

Pumps in Parallel Contd…Pumps in Parallel Contd…

Pump SelectionPump Selection

• System HeadSystem Head•   Definition:Definition:

– Total head imposed on a pump by the Total head imposed on a pump by the irrigation system also called TDH (Total irrigation system also called TDH (Total Dynamic Head), total pumping head, Dynamic Head), total pumping head, etc.etc.

• ComponentsComponents• Static Head (Elevation Head): elevation Static Head (Elevation Head): elevation

difference between water level on the difference between water level on the inlet side and the water delivery pointinlet side and the water delivery point

Components Cont’d…Components Cont’d…

• Pressure Head: difference in water pressures Pressure Head: difference in water pressures between the source and the delivery pointbetween the source and the delivery point

•   Friction Head: total friction loss between the Friction Head: total friction loss between the source and the delivery pointsource and the delivery point

• Velocity Head: VVelocity Head: V22/(2g) /(2g) (usually considered (usually considered negligible)negligible)

•   System Head = System Head = Static + Pressure + Friction (units of Static + Pressure + Friction (units of

feet)feet)

Components of Total System HeadComponents of Total System Head(or (or TTotal otal DDynamic ynamic HHead, Total Pumping Head)ead, Total Pumping Head)

System Head CurveSystem Head Curve• H increases with increasing Q H increases with increasing Q

because of:because of:– drawdown (wells)drawdown (wells)– frictionfriction– pressure at nozzlespressure at nozzles

•   System head can also vary with System head can also vary with time:time:– water table fluctuationswater table fluctuations– changes in the irrigation systemchanges in the irrigation system– pipe agingpipe aging

System Head CurveSystem Head Curve

Pump Operating PointPump Operating Point • As indicated by its TDH-Q curve, a As indicated by its TDH-Q curve, a

pump can operate at many pump can operate at many possible pointspossible points

•   A pump will operate at a Q and A pump will operate at a Q and TDH determined by the point TDH determined by the point where the pump curve and the where the pump curve and the system head curve crosssystem head curve cross

• The same pump is likely to operate The same pump is likely to operate at two different TDH-Q at two different TDH-Q combinations when placed in two combinations when placed in two different irrigation systemsdifferent irrigation systems

Pump Operating Point in a SystemPump Operating Point in a System

Different Pumps in the Same SystemDifferent Pumps in the Same System

Matching a Pump to the Matching a Pump to the SystemSystem

• General– buyer specifies desired Q and TDH

(usually not the entire system head curve)

– supplier specifies operating characteristics (including pump curves)

– obviously want a high Ep

– can fine tune a match by adjusting speed and/or trimming the impeller

Matching a Pump to the System Matching a Pump to the System Contd…Contd…

• Horizontal Centrifugal Pumps– provide correct Q and TDH at a high Ep

– usually buy off-the-shelf unit

• Vertical Turbine Pumps– choose a bowl and impeller to provide

the desired Q at a high Ep

– determine the number of bowls required to provide the desired TDH (pumps in series)

A vertical turbine pump is needed to deliver 400 gpm from a well A vertical turbine pump is needed to deliver 400 gpm from a well that will have a static pumping lift of 237 feet, plus an operating that will have a static pumping lift of 237 feet, plus an operating pressure of 55 psi at the pump head. Is the WLR 10JKH pump pressure of 55 psi at the pump head. Is the WLR 10JKH pump below a good choice? If so, how many stages are required?below a good choice? If so, how many stages are required?

TDH= 237+(55psi*2.31 ft/psi)=364 ft

@ Q=400 gpm:

TDH=52 ft/stage for 7.7” & Ep=79.5% TDH=41 ft/stage for 7.13” & Ep=77.5%

TDH=30 ft/stage for 6.56” & Ep=72%

364 ft/52 ft/stage=7 stages

The best choice is the 7.7” diameter impeller at 52 ft/stage, because it not only requires the fewest stages (low initial cost), but has the best efficiency (low operating cost) near 80%.

A vertical turbine pump is needed to deliver 400 gpm from a well A vertical turbine pump is needed to deliver 400 gpm from a well that will have a static pumping lift of 237 feet, plus an operating that will have a static pumping lift of 237 feet, plus an operating pressure of 60 psi at the pump head. Is the WLR 10JKH pump pressure of 60 psi at the pump head. Is the WLR 10JKH pump below a good choice? If so, how many stages are required?below a good choice? If so, how many stages are required?

TDH= 237+(55psi*2.31 ft/psi)=364 ft

@ Q=400 gpm:

TDH=52 ft/stage for 7.7” & Ep=79.5% TDH=41 ft/stage for 7.13” & Ep=77.5%

TDH=30 ft/stage for 6.56” & Ep=72%

364 ft/52 ft/stage=7 stages

The best choice is the 7.7” diameter impeller at 52 ft/stage, because it not only requires the fewest stages (low initial cost), but has the best efficiency (low operating cost) near 80%.

Net Positive Suction HeadNet Positive Suction Head

• Suction lift and cavitation•  Handout•  Pump does not "suck" or "pull"

water•  Impeller causes partial vacuum• Atmospheric pressure forces water

up to the impeller• Theoretical vs. practical lift• Describe cavitation

Schematic For NPSHA Versus Atmospheric Pressure

NPSHNPSHaa

• NPSHa = AP - SL - FL - VP– AP = atmospheric pressure– SL = suction lift (vertical distance)– FL = friction loss on suction side– VP = vapor pressure– all have units of feet

Atmospheric Pressure at Various AltitudesAltitude (feet) Absolute Pressure(psi) Absolute Pressure(ft)

0

500

1000

1500

2000

2500

3000

3500

4000

5000

6000

7000

8000

9000

10,000

14.7

14.4

14.2

13.9

13.7

13.4

13.2

12.9

12.7

12.2

11.8

11.3

10.9

10.5

10.1

34.0

33.3

32.8

32.2

31.6

31.0

30.5

29.8

29.4

28.2

27.3

26.2

25.2

24.3

23.4

Vapor Pressure at Various TemperaturesTemperature 0F Vapor Pressure (Feet)

50

60

70

80

90

100

110

130

150

170

190

210

0.4

0.6

0.8

1.2

1.6

2.2

3.0

5.2

8.7

14.2

22.3

34.0

NPSHNPSHrr

• NPSHr is a pump characteristic (increases as Q increases)

• If NPSHa > NPSHr:Design is OK

• If NPSHa < NPSHr: Cavitation will be a

problem (good idea to have a factor of safety)

Power UnitsPower Units• Electric motorsElectric motors

– direct coupleddirect coupled• High Efficiency drive (EHigh Efficiency drive (Edrivedrive=100%), but Fixed Speed=100%), but Fixed Speed

– belt drive belt drive • Variable Speed, but Lower Efficiency drive (EVariable Speed, but Lower Efficiency drive (Edrivedrive= 90%) = 90%)

– rated by output HPrated by output HP

– Em's 90% are common– Em doesn't vary much with load

(unless it's significantly under-loaded)

Epower or energy out (shaft)

power or energy in (electricity)m

Internal Combustion EnginesInternal Combustion Engines• Fuels

– Natural gas– Diesel fuel– Propane– Gasoline

• Right-angle Gear Drives– Convert power in horizontal engine shaft

to power in vertical pump line shaft– Edrive 95% (5% loss through the gear

drive)

Internal Combustion Engines Contd…Internal Combustion Engines Contd…

• Ee varies with engine speed and with the load on the engine

• Ee's rarely exceed 30%

Epower or energy out (shaft)

power or energy in fuel usede

Pumping CostsPumping Costs

Fixed Costs vs. Operating CostsFixed Costs vs. Operating Costs

• Fixed: Fixed: pump, motor/engine, well, other pump, motor/engine, well, other equipmentequipment (total cost is the same (total cost is the same regardless of use)regardless of use)

• Operating: Operating: energy, maintenance, repairs, energy, maintenance, repairs, laborlabor (total cost increases with (total cost increases with increasing use)increasing use)

Overall Pumping Plant Overall Pumping Plant PerformancePerformance

Overall pumping plant efficiency, (EOverall pumping plant efficiency, (Eoo):):

Electric Motor DrivenElectric Motor Driven

– EEoo = E = Epp x E x Emm x E x Edrivedrive

Internal Combustion Engine DrivenInternal Combustion Engine Driven

– EEoo = E = Epp x E x Eee x E x Edrivedrive

Efficiencies are expressed in decimal for this calculation, (%/100)Efficiencies are expressed in decimal for this calculation, (%/100)

Eoutput power or energy (supplied to water)

input power or energy (electricity or fuel)o

Typical Values of Overall Efficiency for Representative Typical Values of Overall Efficiency for Representative Pumping Plants Expressed as PercentPumping Plants Expressed as Percent

Power Power SourceSource

Maximum Maximum Theoretical Theoretical

Recommended as Recommended as AcceptableAcceptable

Avg Values Avg Values from Field Testsfrom Field Tests

Electric 72-77 65 45 – 55

Diesel 20 – 25 18 13 – 15

Natural Gas

18 – 24 15 – 18 9 – 13

Butane, Propane

18 – 24 15 – 18 9 – 13

Gasoline 18 – 23 14 – 16 9 – 12

Annual Pumping Energy CostAnnual Pumping Energy CostElectric Powered Pumping PlantElectric Powered Pumping Plant

– V = volume of water pumped per year, acre-feet

– TDH = total system head, feet

– Eo = overall pumping plant efficiency = %

– Ce= electricity price, $/kilowatt-hour

$/yrkwh

$C x

HP-hr

kwh. x

TDH ft x

%)/( E

V ac-ft x

ac-ft ft

HP-hr. e

o

7460

100

3731

Annual Pumping Energy CostAnnual Pumping Energy CostNatural Gas Engine DrivenNatural Gas Engine Driven Pumping PlantPumping Plant

– V= volume of water pumped per year, acre-feet

– TDH = total system head, feet

– Eo = overall pumping plant efficiency, %

– Cg = natural gas price = $/1000 cubic feet of gas

$/yr ft

$C x

HP-hr

BTU x

BTU

ft x

TDH ft x

%)/(E

V ac-ft x

ac-ft ft

HP-hr. g

o

3

3

1000

2545

1000100

3731

Annual Pumping Energy CostAnnual Pumping Energy CostSimplified EquationsSimplified Equations

Total Seasonal Energy CostsTotal Seasonal Energy Costs Unit Energy CostsUnit Energy Costs

Nat. Gas:Nat. Gas: Energy Cost, $/yr = Energy Cost, $/yr = VV x x TDHTDH x x CCgg Energy Cost, $/ac-in = Energy Cost, $/ac-in =

TDH x CTDH x Cgg

2.862 x E2.862 x Eoo 34.691 x E34.691 x Eoo

Propane:Propane: Energy Cost, $/yr =Energy Cost, $/yr = 3.698 x V x TDH x C 3.698 x V x TDH x Cpp Energy Cost, $/ac-in = Energy Cost, $/ac-in =

TDH x CTDH x Cpp

EEoo 3.278 x E3.278 x Eoo

Diesel:Diesel: Energy Cost, $/yr = Energy Cost, $/yr = 2.496 x V x TDH x C 2.496 x V x TDH x Cdd Energy Cost, $/ac-in = Energy Cost, $/ac-in =

TDH x CTDH x Cdd

EEoo 4.856 x E4.856 x Eoo

Electric:Electric: Energy Cost, $/yr = Energy Cost, $/yr = 102.4 x V x TDH x C 102.4 x V x TDH x Cee Energy Cost, $/ac-in = Energy Cost, $/ac-in =

8.448 x TDH x C8.448 x TDH x Cee

EEoo EEoo

CCgg = cost of natural gas, $/Mcf = cost of natural gas, $/Mcf

CCpp = cost of propane, $/gal = cost of propane, $/gal V = volume of water pumped, acre-feetV = volume of water pumped, acre-feet

CCdd = cost of diesel, $/gal = cost of diesel, $/gal TDH = total pumping head, ftTDH = total pumping head, ft

CCee = cost of electricity, $/kWh = cost of electricity, $/kWh EEoo = overall pumping plant efficiency, % = overall pumping plant efficiency, %

Nebraska Pumping Plant Nebraska Pumping Plant Performance CriteriaPerformance Criteria

• “Target" for a system that is well designed and operated (can be exceeded)

•  Calculated based on reasonable values for Ep, Em, Ee, Edrive, energy content of fuel, etc.

PCenergy output

energy input

water horsepower - hours

energy unit

Nebraska Pumping Plant Nebraska Pumping Plant Performance Criteria Contd…Performance Criteria Contd…

• “energy unit" : – kilowatt-hour (electricity)– gallon (diesel, propane, gasoline)– 1000 cubic feet (mcf) (natural gas)

• performance rating = PR = (actual performance) / (performance criteria)

Nebraska Performance Nebraska Performance CriteriaCriteria

• Q = 800 gpm• TDH = 218 feet• diesel fuel consumption = 4 gallons per

hour• performance rating? -- Equation 7.12• gallons of fuel per acre-inch of water

pumped? -- Equation 7.14(800 gpm)(216 ft) 44 whp

3960

Nebraska Performance Criteria Nebraska Performance Criteria Contd…Contd…

• performance = (44 whp) / (4 gal/hr) = 11 whp-hr/gal

• performance criteria = PC = 12.5 whp-hr/gal

• performance rating = PR = 11 / 12.5 = 0.88

E = TDH

(8.75)(PC)(PR) =

218

(8.75)(12.5)(0.88) = 2.26 gal / ac - in

Head Capacity Curve for Centrifugal Pump With Various Pump SpeedsHead Capacity Curve for Centrifugal Pump With Various Pump Speeds