1. Centrifugal Pumps Operation, Selection, Types, Performance

2. Types of Pumps Positive displacement pumps Centrifugal 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)

3. Rotating Impeller Converts Mechanical Energy to Hydraulic Energy

4. Centrifugal Pump Impellers
Enclosed Impeller
Semi-Open Impeller

5. Centrifugal 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

6. Typical Horizontal Centrifugal Pump Installation

7. Horizontal Centrifugal Pumps

8. 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

9. Vertical Turbine Pump

10. Single-Stage Vertical Turbine Pump
Water Flow Path Through a One-Stage Vertical Turbine Pump

11. Two-Stage Vertical Turbine Pump
Water Flow Path Through a Two-Stage Vertical Turbine Pump

12. (Discharge Heads)
Gearhead for engine drive
Holloshaft electric motor

13. 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
For deep household water wells, the submersible electric pump is the most common choice. The pump has several stages to generate enough pressure to lift the water out of the well and to pressurize is sufficiently for household use. The electric motor is long and narrow so it can fit down small household wells as small as 4 inches in diameter.

14. Head Capacity Curve (Fig. 8.6)

15. Pump 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

16. 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

17. Pump Characteristics Contd…
Brake horsepower vs. Discharge
where: Q, (gpm); TDH, (ft); bhp & whp, (HP)
Combined characteristic curves
Horizontal centrifugal pump
Vertical turbine pump

18. Vertical Turbine Pump Performance Curve

19. Horizontal Centrifugal Pump Performance Curve

20. 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

21. 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= RPM2= RPM2/RPM1=1.11
Q2/Q1= RPM2/RPM1 Q2= Q1 x RPM2/RPM1 = 200 x 1.11= 222 gpm
TDH2/TDH1=[RPM2/RPM1] 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

22. Affinity Laws Contd… Impeller diameter Ep may change a little
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)

23. Pumps in Series Booster pump Multi-stage turbine pump Q1 = Q2
 TDHtot = TDH1 + TDH (add heads at the same discharge)
 bhptot = bhp1 + bhp2

24. Pumps in Series Cont’d…

25. Pumps in Parallel

26. Pumps in Parallel Contd…
Qtot = Q1 + Q (add discharges at the same head)
bhptot = bhp1 + bhp2

27. Pumps in Parallel Contd…

28. Pump Selection System Head Definition: Components
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 side and the water delivery point

29. Components Cont’d…
Pressure Head: difference in water pressures between 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)

30. Components of Total System Head
(or Total Dynamic Head, Total Pumping Head)

31. System Head Curve H increases with increasing Q because of:
drawdown (wells)
friction
pressure at nozzles
 System head can also vary with time:
water table fluctuations
changes in the irrigation system
pipe aging

32. System Head Curve

33. Pump Operating Point
As indicated by its TDH-Q curve, a pump can operate at many possible points
 A pump will operate at a Q and TDH determined by the point where the pump curve and the system head curve cross
The same pump is likely to operate at two different TDH-Q combinations when placed in two different irrigation systems

34. Pump Operating Point in a System

35. Different Pumps in the Same System

36. Matching a Pump to the System
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

37. Matching a Pump to the System 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)

38. 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=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%.

39. 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=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%.

40. Net 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

41. Schematic For NPSHA Versus Atmospheric Pressure

42. 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

43. Atmospheric Pressure at Various Altitudes
Altitude (feet)
Absolute Pressure(psi)
Absolute Pressure(ft)
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

44. Vapor Pressure at Various Temperatures
Temperature 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

45. NPSHr 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)

46. Power Units Electric motors direct coupled belt drive
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
Em doesn't vary much with load (unless it's significantly under-loaded)

47. 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
Edrive  95% (5% loss through the gear drive)

48. Internal Combustion Engines Contd…
Ee varies with engine speed and with the load on the engine
Ee's rarely exceed 30%

49. Fixed Costs vs. Operating Costs
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)

50. Overall Pumping Plant Performance
Overall pumping plant efficiency, (Eo):
Electric Motor Driven
Eo = Ep x Em x Edrive
Internal Combustion Engine Driven
Eo = Ep x Ee x Edrive
Efficiencies are expressed in decimal for this calculation, (%/100)

51. Recommended as Acceptable Avg Values from Field Tests
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
45 – 55
Diesel
20 – 25 18
13 – 15
Natural Gas
18 – 24
15 – 18
9 – 13
Butane, Propane
Gasoline
18 – 23
14 – 16
9 – 12

52. Annual Pumping Energy Cost Electric 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

53. Annual Pumping Energy Cost Natural Gas Engine Driven Pumping 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

54. Annual Pumping Energy Cost Simplified Equations
Total Seasonal Energy Costs Unit Energy Costs
Nat. Gas: Energy Cost, $/yr = V x TDH x Cg Energy Cost, $/ac-in = TDH x Cg
2.862 x Eo x Eo
Propane: Energy Cost, $/yr = x V x TDH x Cp Energy Cost, $/ac-in = TDH x Cp
Eo x Eo
Diesel: Energy Cost, $/yr = x V x TDH x Cd Energy Cost, $/ac-in = TDH x Cd
Eo x Eo
Electric: Energy Cost, $/yr = x V x TDH x Ce Energy Cost, $/ac-in = x TDH x Ce
Eo Eo
Cg = cost of natural gas, $/Mcf
Cp = cost of propane, $/gal V = volume of water pumped, acre-feet
Cd = cost of diesel, $/gal TDH = total pumping head, ft
Ce = cost of electricity, $/kWh Eo = overall pumping plant efficiency, %

55. Performance 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.

56. 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)

57. Performance Criteria 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

58. Performance Criteria 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

59. Head Capacity Curve for Centrifugal Pump With Various Pump Speeds