Performance And Design Characteristics Of Airlift Pumps .

Research ReportPerformance and design characteristicsof airlift pumps for field applicationsClick here for Rectangular Airlift DesignWilliam A. Wurts,(1) Sam G. McNeill(2) and Douglas G. Overhults(2)Individual and combined pumping capacities were determined for floating airlift pumps, powered by acentrifugal blower. Individual airlift pumping rates ranged from 66-225 liters of water per minute (L/min)for all variables examined. Airlift pumps, 185 cm long, were made from PVC pipe of 7.6, 10.2 and 15.2 cminner diameters. Air was injected through a 2.5-cm pipe at 50, 65, and 80 cm below the water dischargeoutlet. Water flow rates were measured at differing air flow injection rates (71-324 L/min). Individual airliftpumping rates increased as pipe diameter, air flow and air injection depth increased. Using the data fromthese experiments and a manufacturer's performance curve, it was calculated that a 1.0-horsepower (0.75 kw)centrifugal blower could pump 3107 ñ 75 (SD) L/min water by combining the individual outputs of twentyeight 7.6-cm diameter airlift pumps. To achieve this total, each airlift would require 71 L/min air flowinjected at 80 cm depth (82.6 cm water pressure) to pump 111 L/min water.Introductionpurpose of this study (7) was to test airlift pumpingcharacteristics for a specific design configuration and todetermine reasonable expectations of water pumping capacityunder practical field conditions.The theory and principle of airlift pumps weredescribed in detail by Nicklin.(5) From a simple conceptualviewpoint, air bubbles act as pneumatic pistons, pushing orMethodsdrawing water up a pipe or stack as they rise and expand. Amore precise explanation describes the pumping action as theresult of an air-water mixture. The air-water mixture is lessAirlift pumps were constructed from commonly useddense than and therefore is displaced by the surroundingand readily available materials and equipment (PVC andwater of higher density.polyethylene pipes, PVC fittings, stainless steel ring-clampsAirlift pumps are widely used by aquaculturists.and a centrifugal blower). Pumping capacities wereCommon airlift applications are to pump,circulate and aerate water in closed,recirculating systems as well as in ponds.Several researchers have examined theperformance characteristics of airlift pumpsused for aquacultural applications. Castro etal.(4) and Castro and Zielinski(3) studiedperformance for 1.27-8.0 cm diameterairlifts at different levels of submergence(40-100%) in water tanks. Parker andSuttle(6) examined the performancecharacteristics of 3.75-30 cm diameter airliftpumps at various air flow rates and airinjection depths at 100% submergence (levelflow) in ponds, and concluded that 7.6-10cm diameter pumps were the most practical.Centrifugal blowers are one of themost effective and inexpensive methods toproduce or pump air because they producerelatively high volumes of air at lowABCoperating pressures. One might concludefrom the results of Parker and Suttle (6) thatindividual, large-diameter pipes are the mosteffective airlift pumps. However, that doesFigure 1. General diagrams of three basic airlift pump designs.not take into consideration actual, and mostefficient, blower operating pressures. TheWorld Aquaculture 25(4)December 199451

determined for floating airliftpumps (Fig. 1A, basic test9"configuration) powered by a 2.5hp (1.9 kw) centrifugal blower.Airlift pumps, 185 cm long, weremade from PVC pipes of 7.6,To U-Tube10.2 and 15.2 cm innerB. 1 inch Valvediameters.Air was injected("P" Adjustment)A. 1 inch Valvethrougha2.5-cminner diameter(Air Flow Rate Adjustment)pipe(14.2mlong)at 50, 65, andC. 1 inch ValveTo Airlift80 cm below the discharge outlet.The bottom of the dischargeTo BlowerTo Airliftoutlet ranged from 0-2.5 cmManifoldabove the water surface and wasbuoyed with foam flotation. AirMaterials: 3 each Valves, PVC, 1 inch PVC Glue Socket3 each Adapter, PVC, 1 inch Socket to Threadedflow rates were varied between2 each TEE, PVC, 1 inch Socket2 each Adapter 'Barb', 1 inch Threaded to 1 inch Polyethylene Hose71 and 324 liters per minute1 each Adapter 'Barb', 1 inch to 3/8 inch Inch HosePipe, PVC Schedule 40, 1 Inch(L/min) and corresponding waterHose, Polyethylene, 1 InchHose, 3/8 Inchflow rates were measured.Operatingpressureswererecorded for each airflow rateFigure 2. Air pressure flow regulator system for testing and adjusting air flowtested.rates at various operating pressures.Air flow rates and operating (in-line) airpressures were measured with a hot wire anemometer, aU-tube manometer and an air pressure/flow regulatorsystem constructed from 2.5-cm PVC pipe and gate valves(Fig. 2). System operating pressures were determined foreach injection depth and approximate air flow rate beforeadjusting actual air flow rates. Once operating pressurewas determined, valve C was closed and valve A was usedto adjust air flow while adjusting air pressure with valve B(Fig. 2). After air flow had been adjusted for theappropriate pressure, valve C was opened, valve B wasclosed and water flow was then measured. Air and watertemperatures were between 27 and 32øC. The study wasconducted in a 0.13 ha pond (2.44 m deep) at 173.7 mabove sea level.Water flow was calculated by measuring the timerequired to fill a 127-L, rigid plastic container. Fivemeasurements were collected and timed for eachcombination of pipe diameter, air flow and air injectiondepth. Mean and standard deviation were calculated foreach of the five water flow rates observed. Flow rates forair and water were plotted and compared with linear,power, exponential and logarithmic regressions.Entry Hole ForHot WireAnemometerResults and DiscussionLogarithmic regression (y b m*1nx) had thebest fit with the data collected (Fig. 3). Values for thecoefficient of determination (R2) ranged from 0.82 to0.998. Overall, individual airlift pumping rates increasedFigure 3. Regression (y b m*lnx) and data plotsof air flow and mean water flow rates for threeinjection depths (50, 65 and 80 cm) and airlift pipediameters (7.6, 10.2 and 15.2 cm).World Aquaculture 25(4)December 199452

Table 1. Mean water flow rates and corresponding standard deviations produced at various airinjection depths, operating pressures and air flow rates in 7.6 (A), 10.2 (B) and 15.2 cm (C)inner diameter airlift pumps.Injectiondepth (cm)A. 506580B. 506580C. 506580World Aquaculture 25(4)Pressure(cm H2O)Air flow(liters/min)Water 125.2155.2163.9 2.5 0.9 1.4 1.4 2.7 2.6 3.3 1.5 2.7 3.3 2.1 78.696.2120.5175.1105.1124.2146.9224.8 5.9 1.4 1.1 1.9 3.1 3.8 4.8 4.0 1.9 1.0 3.1 .5224.0 23.0163.6181.7210.3--- 3.9 1.2 1.9 2.5 2.2 5.2 4.7 4.0 2.1 2.8 5.8 3.9 5.8 6.2December 199453

3 inch PVC TEE1 inch BlackPolyethylene HoseTo BlowerManifoldFloatinjection line. Back pressure develops as a result ofline resistance (friction), and is the most plausibleexplanation for the observed operating pressuresexceeding corresponding air injection depths in thepresent study. The most notable example wasobserved when air was injected, at a flow rate of 324L/min and 65 cm depth, into the 15.2 cm airlift.Operating pressure increased by 16 cm water overthat observed for the lowest air flow rate (115 L/min)tested at the same injection depth and airlift diameter(Table 1).3 inch PVC PipeConclusionsAir Injection at WaterDepth of 30 to 32 inchesWhile high air flow rates injected into largediameterairlift pumps may generate impressive water1 inch PVC Pipe1-1/2 inch X 3 inch Teeflow rates, they also produce dramatic increases in airand Fittingsinjection line back pressure. As noted by Parker andSuttle,(6) pressure increases of several centimetersIntake Depth Determinedby Pond Depthwater can substantially reduce airlift performanceefficiency. As operating pressure increases, total airoutput can decrease significantly in centrifugalFigure 4. A design of an easily constructed 7.6 cm diameter airliftblowers, particularly for blowers rated at 2.5 hp (1.9de-stratifying pump.kw) or less.Using standard manufacturers'performance curves for commercially available, 1.0as pipe diameter, air flow and air injection depth increased.hp (0.75 kw) centrifugal blowers and the data in Table 1, itIndividual airlift pumping rates ranged from 66-225 L/minwas calculated that the highest water pumping rates (2775water for all variables examined. Operating pressures were 03107 L/min) could be achieved by combining the individual21.6 cm water greater than corresponding injection depths andoutputs of 25 to 28, 7.6-cm diameter airlifts. Each airliftincreased as air flow increased (Table 1).would require 71 L/min air flow (at 82.6 cm water pressure)While the water flow rates measured in this studyinjected at 80 cm depth to pump 111 L/min water.were good, they were somewhat lower than the findings ofAirlift pumps appear to have excellent potential forParker and Suttle.(6) It is difficult to determine whether theuse in cages, floating raceways, closed or recirculatingpumping rates observed by Parker and Suttle(6) weresystems, and for pond de-stratification or aeration. Somesignificantly greater than those observed in the present studygeneral design schematics are depicted in Figure 1A, B and C.without an indication of data set variability. The discrepanciesEach configuration would have a more practical useobserved in this study may relate to placement of thedepending on system design or construction and the intendeddischarge pipe at slightly less than 100% submergence (0 toapplication. Figure 1A might be better suited for construction2.5 cm above water level), longer pipe lengths (185 vs. 130of airlift cages (in-frame) while 1C would be more practicalcm) and different test equipment (Figure 1A vs. 1B, andfor floating airlift de-stratifiers. The basic design presented inFigure 2). Parker and Suttle(6) demonstrated that water flowFigure 1B could facilitate incorporation of multiple airliftrates in 5 to 10-cm airlifts increased as much as 12 to 38%outputs into a common, floating reservoir (e.g. a raceway) orwhen the water discharge pipe was lowered from 1.25 cminto a closed, recirculating system. Figure 4 is a diagram of anabove the water surface, to a position level with or slightlyeasily constructed, floating airlift de-stratifier which willbelow the water surface. Equations used by Castro andclosely parallel the performance characteristics of the pumpsZielinski(3) predicted the maximum water flow rates possibletested in this study.for a given pipe diameter and percent submergence, but do notpredict water flows for various air injection depths at virtual100% (98.6-100%) submergence.AcknowledgmentsOf practical importance, but not readily apparentfrom the findings of Parker and Suttle,(6) is that operating orWe gratefully acknowledge John Earnest for developing CADsystem in-line pressure increases as air flow increases. Forgraphics of the original sketches.any given air flow rate, the in-line pressure increases as lengthof the air injection pipe increases and as pipe diameterNotes and Referencesdecreases (7.6 vs 2.5 vs 1.25 cm). Air flow rates of 36.8 and73.1 L/min, or greater, would create turbulent flow and back1. Cooperative Extension Program, Kentucky Statepressure in 1.25- and 2.5-cm inner diameter air lines,University, P. O. Box 469, Princeton, Kentucky 42445respectively. An air flow rate of 1,138 L/min(6) would0469 USA.generate significant back pressure in a 1.25-cm diameterWorld Aquaculture 25(4)December 199454

2.3.4.Cooperative Extension Service, University of Kentucky,P. O. Box 469, Princeton, Kentucky 42445-0469 USA.Castro WE, Zielinski PB. 1980. Proc. World MaricultureSoc. 11:163-174.Castro WE, Zielinski PB, Sandifer PA. 1975. Proc. WorldMariculture Soc. 6:451-461.World Aquaculture 25(4)5.6.Nicklin, DJ. 1963. Trans. Inst. Chem. Engrs 41:29-39.Parker NC, Suttle MA. 1987. Aquacul. Engineer.6:971107.7. Wurts WA, Overhults DG, McNeill SG. 1990. Ann. Mtg.World Aq. Soc., Halifax, Nova Scotia.Book ofAbstracts, p. 36.December 199455

William A. Wurts,(1) Sam G. McNeill(2) and Douglas G. Overhults(2) Individual and combined pumping capacities were determined for floating airlift pumps, powered by a centrifugal blower. Individual airlift pumping rates ranged from 66-225 liters of water per mi