Pumping Plants

Types 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 Energy to Hydraulic Energy

Centrifugal Pump Impellers Enclosed ImpellerSemi-Open Impeller

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

Typical Horizontal Centrifugal Pump Installation

Horizontal Centrifugal Pumps

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 Pump

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

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

Gearhead for engine drive Holloshaft electric motor (Discharge Heads)

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

Head Capacity Curve (Fig. 8.6)

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

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

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

Vertical Turbine Pump Performance Curve

Horizontal Centrifugal Pump Performance Curve

Affinity Laws Speed – Law applies to virtually all irrigation pumps – E p may be affected a little, but not as predictable – Ways of changing speeds: pulleys, gear ratios, throttle, change motor

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? RPM 1 =1800 RPM 2 = 2000 RPM 2 /RPM 1 =1.11 Q 2 /Q 1 = RPM 2 /RPM 1 Q 2 = Q 1 x RPM 2 /RPM 1 = 200 x 1.11= 222 gpm TDH 2 /TDH 1 =[RPM 2 /RPM 1 ] 2 TDH 2 = TDH 1 x [RPM 2 /RPM 1 ] 2 TDH 2 = 150 x [1.11] 2 = 185 feet BHP 2 /BHP 1 = =[RPM 2 /RPM 1 ] 3 BHP 2 = BHP 1 x [RPM 2 /RPM 1 ] 3 BHP 2 = 10 x [1.11] 3 = 13.7 HP

Affinity Laws Contd… Impeller diameter – Law strictly applies only to horizontal centrifugal pumps, but good approximation for vertical turbine pumps E p may change a little Diameter is changed by trimming the impeller (law holds up to about 10-20% trim)

Pumps in Series Booster pump Multi-stage turbine pump Q 1 = Q 2 TDH tot = TDH 1 + TDH 2 (add heads at the same discharge) bhp tot = bhp 1 + bhp 2

Pumps in Series Cont’d…

Pumps in Parallel

Pumps in Parallel Contd… Q tot = Q 1 + Q 2 (add discharges at the same head) bhp tot = bhp 1 + bhp 2

Pumps in Parallel Contd…

Pump Selection System Head System Head Definition: Definition: – Total head imposed on a pump by the irrigation system also called TDH (Total Dynamic Head), total pumping head, etc. Components Components Static Head (Elevation Head): elevation difference between water level on the inlet side and the water delivery point Static Head (Elevation Head): elevation difference between water level on the inlet side and the water delivery point

Components Cont’d… Pressure Head: difference in water pressures between the source and the delivery point 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 Friction Head: total friction loss between the source and the delivery point Velocity Head: V 2 /(2g) (usually considered negligible) Velocity Head: V 2 /(2g) (usually considered negligible) System Head = Static + Pressure + Friction (units of feet) System Head = Static + Pressure + Friction (units of feet)

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

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

System Head Curve

Pump Operating Point As indicated by its TDH-Q curve, a pump can operate at many possible points 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 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 The same pump is likely to operate at two different TDH-Q combinations when placed in two different irrigation systems

Pump Operating Point in a System

Different Pumps in the Same System

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

Matching a Pump to the System Contd… Horizontal Centrifugal Pumps – provide correct Q and TDH at a high E p – usually buy off-the-shelf unit Vertical Turbine Pumps – choose a bowl and impeller to provide the desired Q at a high E p – 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 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 Q=400 gpm: TDH=52 ft/stage for 7.7” & E p =79.5% TDH=41 ft/stage for 7.13” & E p =77.5% TDH=30 ft/stage for 6.56” & E p =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 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 Q=400 gpm: TDH=52 ft/stage for 7.7” & E p =79.5% TDH=41 ft/stage for 7.13” & E p =77.5% TDH=30 ft/stage for 6.56” & E p =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 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

NPSH a NPSH a = 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 Altitude (feet)Absolute Pressure(psi)Absolute Pressure(ft) ,

Vapor Pressure at Various Temperatures Temperature 0 FVapor Pressure (Feet)

NPSH r NPSH r is a pump characteristic (increases as Q increases) If NPSH a > NPSH r : Design is OK If NPSH a < NPSH r : Cavitation will be a problem (good idea to have a factor of safety)

Power Units Electric motors Electric motors – direct coupled High Efficiency drive (E drive =100%), but Fixed Speed High Efficiency drive (E drive =100%), but Fixed Speed – belt drive Variable Speed, but Lower Efficiency drive (E drive = 90%) Variable Speed, but Lower Efficiency drive (E drive = 90%) – rated by output HP – E m 's  90% are common – E m doesn't vary much with load (unless it's significantly under-loaded)

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 – E drive  95% (5% loss through the gear drive)

Internal Combustion Engines Contd… E e varies with engine speed and with the load on the engine E e 's rarely exceed 30%

Pumping Costs Fixed Costs vs. Operating Costs Fixed: pump, motor/engine, well, other equipment (total cost is the same regardless of use) 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) Operating: energy, maintenance, repairs, labor (total cost increases with increasing use)

Overall Pumping Plant Performance Overall pumping plant efficiency, (E o ): Electric Motor Driven – E o = E p x E m x E drive Internal Combustion Engine Driven – E o = E p x E e x E drive Efficiencies are expressed in decimal for this calculation, (%/100)

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 – 55 Diesel20 – – 15 Natural Gas 18 – 2415 – 189 – 13 Butane, Propane 18 – 2415 – 189 – 13 Gasoline18 – 2314 – 169 – 12

Annual Pumping Energy Cost Electric Powered Pumping Plant – V = volume of water pumped per year, acre-feet – TDH = total system head, feet – E o = overall pumping plant efficiency = % – C e = electricity price, $/kilowatt-hour

Annual Pumping Energy Cost Natural Gas Engine Driven Pumping Plant – V= volume of water pumped per year, acre-feet – TDH = total system head, feet – E o = overall pumping plant efficiency, % – C g = natural gas price = $/1000 cubic feet of gas

Annual Pumping Energy Cost Simplified Equations Total Seasonal Energy CostsUnit Energy Costs Nat. Gas: Energy Cost, $/yr = V x TDH x C g Energy Cost, $/ac-in = TDH x C g Nat. Gas: Energy Cost, $/yr = V x TDH x C g Energy Cost, $/ac-in = TDH x C g x E o x E o x E o x E o Propane: Energy Cost, $/yr = x V x TDH x C p Energy Cost, $/ac-in = TDH x C p E o x E o E o x E o Diesel: Energy Cost, $/yr = x V x TDH x C d Energy Cost, $/ac-in = TDH x C d E o x E o E o x E o Electric: Energy Cost, $/yr = x V x TDH x C e Energy Cost, $/ac-in = x TDH x C e E o E o E o E o C g = cost of natural gas, $/Mcf C p = cost of propane, $/galV = volume of water pumped, acre-feet C d = cost of diesel, $/galTDH = total pumping head, ft C e = cost of electricity, $/kWhE o = overall pumping plant efficiency, %

Nebraska Pumping Plant Performance Criteria “Target" for a system that is well designed and operated (can be exceeded) Calculated based on reasonable values for E p, E m, E e, E drive, energy content of fuel, etc.

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 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

Nebraska 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

Head Capacity Curve for Centrifugal Pump With Various Pump Speeds