Bahan Kuliah Pompa Centrifugal

5/22/2018 Bahan Kuliah Pompa Centrifugal

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Pompa Centrifugal


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DynamicPositive

Displacement

Centrifugal Special effect Rotary Reciprocating

Internalgear

Externalgear

Lobe Slidevane

Others (e.g.Impulse, Buoyancy)

Pumps

DynamicPositive

Displacement

Centrifugal Special effect Rotary Reciprocating

Internalgear

Externalgear

Lobe Slidevane

Others (e.g.Impulse, Buoyancy)

Pumps


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Types of Pumps

Positive displacement pumps

Rotary (gear, screw, etc.)

Reciprocating (piston, diaphragm, etc.)

Used as injection and sprayer pumps, butnot for irrigation water

Centrifugal pumps

Rotating impeller converts mechanicalenergy into hydraulic energy (showexamples and transparency)


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Rotating Impeller Converts Mechanical

Energy to Hydraulic Energy


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Centrifugal Pump Impellers

Enclosed Impeller Semi-Open Impeller


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Centrifugal Pumps

Horizontal

Drive shaft is horizontal

Often used when pumping from a surfacesource (pond, lake, stream, etc.), Or forboosting the pressure in an irrigation pipeline(booster pump)

Usually sold as completely assembled units


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Typical Horizontal Centrifugal Pump Installation


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Horizontal

Centrifugal Pumps


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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


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Vertical Turbine Pump


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Single-Stage Vertical Turbine Pump

Water Flow Path

Through a One-Stage



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Two-Stage Vertical Turbine Pump

Water Flow PathThrough a Two-Stage



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Gearhead for

engine drive

Holloshaft electric

motor

(Discharge Heads)


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Submersible Water Pumps

-Same as vertical turbine

pump design

-Driven from below by

electric motor

-Good for deep wells

-High efficiency

-Wells as small as 4 diameter


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Head Capacity Curve


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Pump Characteristics

Head vs. discharge

discharge (or capacity): volume of waterpumped 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


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Pump Characteristics Contd

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


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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

)


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Vertical Turbine Pump Performance Curve


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Horizontal Centrifugal Pump Performance Curve


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Affinity Laws

Speed

Law applies to virtually all irrigation pumps

Epmay be affected a little, but not as predictable

Ways of changing speeds:pulleys, gear ratios, throttle, change motor

QQ

RPMRPM

TDHTDH

RPMRPM

bhpbhp

RPMRPM

2

1

2

1

2

1

2

1

2

1

2

1

2 3


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Affinity Law Example

A 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= Q1x 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= 10x [1.11]

3 = 13.7 HP


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Affinity Laws Contd

Impeller diameter Law strictly applies only to horizontal centrifugal

pumps, but good approximation for vertical turbinepumps

Epmay 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


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Pumps in Series

Booster pump

Multi-stage turbine pump

Q1= Q2

TDHtot= TDH1+ TDH2(add heads at the same discharge)

bhptot= bhp1+ bhp2

tot

tot

pbhp

TDHQ

E 3960)(

Pumps in Series Contd


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Pumps in Series Cont d

P i P ll l


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Pumps in Parallel


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Pumps in Parallel Contd

Qtot= Q1+ Q2(add discharges at the same head)

bhptot

= bhp1

+ bhp2

E

Q H

bhpp

tot

tot

( )

3960


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Pumps in Parallel Contd


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Pump Selection

System Head

Definition:

Total head imposed on a pump by the irrigation

system also called TDH (Total Dynamic Head),total pumping head, etc.

Components

Static Head (Elevation Head): elevation

difference between water level on the inlet sideand the water delivery point


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Components Contd

Pressure Head: difference in water pressuresbetween the source and the delivery point

Friction Head: total friction loss between the source

and the delivery point Velocity Head: V2/(2g) (usually considered negligible)

System Head =Static + Pressure + Friction (units of feet)


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Components of Total System Head

(or Total Dynamic Head, Total Pumping Head)


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System Head Curve

H increases with increasing Qbecause of:

drawdown (wells)

friction

pressure at nozzles

System head can also vary withtime:

water table fluctuations

changes in the irrigation system

pipe aging

S t H d C


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System Head Curve


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Pump Operating Point

As indicated by its TDH-Q curve, a

pump can operate at many possiblepoints

A pump will operate at a Q and TDH

determined by the point where thepump curve and the system headcurve cross

The same pump is likely to operate attwo different TDH-Q combinationswhen placed in two different

irrigation systems

P O ti P i t i S t


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Pump Operating Point in a System

Diff t P i th S S t


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Different Pumps in the Same System


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Matching a Pump to theSystem

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 speedand/or trimming the impeller


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Matching a Pump to the SystemContd

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 toprovide the desired TDH (pumps in series)


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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

pressure of 55 psi at the pump head. Is the WLR 10JKH pump

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=30 ft/stage for 6.56 & Ep=72%

364 ft/52 ft/stage=7 stages

The best choice is the 7.7 diameterimpeller 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%.


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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

pressure of 60 psi at the pump head. Is the WLR 10JKH pump

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=30 ft/stage for 6.56 & Ep=72%

364 ft/52 ft/stage=7 stages

The best choice is the 7.7 diameterimpeller 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%.


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Net Positive Suction Head

Suction lift and cavitation Handout

Pump does not "suck" or "pull" water

Impeller causes partial vacuum

Atmospheric pressure forces water upto the impeller

Theoretical vs. practical lift

Describe cavitation

S h ti F NPSHA V At h i P


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Schematic For NPSHA Versus Atmospheric Pressure


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NPSHa

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 Altitudes


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

0

500

1000

1500

2000

2500

3000

3500

4000

5000

60007000

8000

9000

10,000

14.7

14.4

14.2

13.9

13.7

13.4

13.2

12.9

12.7

12.2

11.811.3

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

27.326.2

25.2

24.3

23.4

Vapor Pressure at Various Temperatures


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Vapor Pressure at Various Temperatures

Temperature 0F Vapor Pressure (Feet)

5060

70

80

90

100

110

130150

170

190

210

0.40.6

0.8

1.2

1.6

2.2

3.0

5.28.7

14.2

22.3

34.0


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NPSHr

NPSHris 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)


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Power Units

Electric motors

direct coupled High Efficiency drive (Edrive=100%), but Fixed Speed

belt drive Variable Speed, but Lower Efficiency drive (Edrive= 90%)

rated by output HP

Em's

90% are common Emdoesn't vary much with load

(unless it's significantly under-loaded)

Epower or energy out (shaft)

power or energy in (electricity)m


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Internal 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

Edrive95% (5% loss through the gear drive)


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Internal Combustion Engines Contd

Eevaries with engine speed and with theload on the engine

Ee's rarely exceed 30%

Epower or energy out (shaft)

power or energy in fuel usede


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Pumping Costs

Fixed Costs vs. Operating Costs

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

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

Overall Pumping Plant


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Overall Pumping PlantPerformance

Overall pumping plant efficiency, (Eo):

Electric Motor Driven

Eo= Epx Emx Edrive

Internal Combustion Engine Driven Eo= Epx Eex Edrive

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


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Typical Values of Overall Efficiency for Representative

Pumping Plants Expressed as Percent

Power

Source

Maximum

Theoretical

Recommended as

Acceptable

Avg Values from

Field Tests

Electric 72-77 65 4555

Diesel 2025 18 1315

Natural

Gas

1824 1518 913

Butane,Propane

1824 1518 913

Gasoline 1823 1416 912


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Annual Pumping Energy CostElectric 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

$Cx

HP-hr

kwh.x

TDH ftx

%)/( E

V ac-ftx

ac-ft ft

HP-hr. e

o

7460

100

3731

Annual Pumping Energy Cost


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Natural Gas Engine DrivenPumping 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

$/yrft

$Cx

HP-hr

BTUx

BTU

ftx

TDH ftx

%)/(E

V ac-ftx

ac-ft ft

HP-hr. g

o

3

3

1000

2545

1000100

3731



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Annual Pumping Energy CostSimplified Equations

Total Seasonal Energy Costs Unit Energy Costs

Nat. Gas: Energy Cost, $/yr = Vx TDHx Cg Energy Cost, $/ac-in = TDH x Cg

2.862 x Eo 34.691 x Eo

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

Eo 3.278 x Eo

Diesel: Energy Cost, $/yr = 2.496 x V x TDH x Cd Energy Cost, $/ac-in = TDH x CdEo 4.856 x Eo

Electric: Energy Cost, $/yr = 102.4 x V x TDH x Ce Energy Cost, $/ac-in = 8.448 x TDH x Ce

Eo Eo

Cg= cost of natural gas, $/Mcf

Cp= cost of propane, $/gal V = volume of water pumped, acre-feetCd= cost of diesel, $/gal TDH = total pumping head, ft

Ce= cost of electricity, $/kWh Eo= overall pumping plant efficiency, %

Nebraska P mping Plant


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Nebraska Pumping PlantPerformance Criteria

Target" for a system that is well designedand operated (can be exceeded)

Calculated based on reasonable values for

Ep, Em, Ee, Edrive, energy content of fuel, etc.

PC

energy output

energy input

water horsepower - hours

energy unit


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Nebraska Pumping Plant

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


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Nebraska PerformanceCriteria

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


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Nebraska Performance CriteriaContd

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


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Bahan Kuliah Pompa Centrifugal

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