Hydraulic Pumps
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Transcript of Hydraulic Pumps
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Hydraulic PumpsHydraulic Pumps
Positive Displacement DevicesPositive Displacement DevicesDisplacement FormulaeDisplacement Formulae
CharacteristicsCharacteristics
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Gear PumpsGear Pumps(External Gear)(External Gear)
Pumping MechanismPumping Mechanism
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Gear PumpsGear Pumps(External Gear)(External Gear)
Displacement parameters and Displacement parameters and determinationdetermination
Displacement = Displacement = ππ/4(D/4(Doo22 – D – Dii
22)L)LDDoo = = Outer diameter of the two gearsOuter diameter of the two gearsDDii = = Inner diameter of the two gearsInner diameter of the two gears
(Actually it is the diameter of the circle defined (Actually it is the diameter of the circle defined by the center of one gear and the outer by the center of one gear and the outer diameter of the other.)diameter of the other.)
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Gear PumpsGear Pumps(External Gear)(External Gear)
Advantages:Advantages:Cheap (easy to manufacture)Cheap (easy to manufacture)CompactCompactCheapCheap
Did I say inexpensive?Did I say inexpensive?
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Gear PumpsGear Pumps(External Gear)(External Gear)
DisadvantagesDisadvantages Limited pressure Limited pressure
capabilitycapability Unbalanced (note Unbalanced (note
where pressure is) where pressure is) Results in large Results in large bearing loadsbearing loads
Can be noisy (gear Can be noisy (gear mesh noise)mesh noise)
Volumetric efficiency?Volumetric efficiency? Fixed DisplacementFixed Displacement
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Gear PumpsGear Pumps(Internal Gear)(Internal Gear)
Pumping Pumping MechanismMechanism
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Gear PumpsGear Pumps(Internal Gear)(Internal Gear)
Displacement is a function of the number Displacement is a function of the number of teeth on the internal and external gears of teeth on the internal and external gears and the size of the crescent divider.and the size of the crescent divider.
( I don’t have a formula for the ( I don’t have a formula for the displacement. Perhaps you can derive displacement. Perhaps you can derive one.)one.)
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Gear PumpsGear Pumps(Internal Gear)(Internal Gear)
AdvantagesAdvantagesSimilar to external gear pumps in many Similar to external gear pumps in many
respectsrespectsQuieter as gear slap is reducedQuieter as gear slap is reduced
DisadvantagesDisadvantagesSomewhat more difficult to manufactureSomewhat more difficult to manufactureSame issues of volumetric efficiencySame issues of volumetric efficiencySame issues of unbalanced forcesSame issues of unbalanced forcesFixed displacementFixed displacement
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Gear PumpsGear Pumps(Internal Gear - Gerotor)(Internal Gear - Gerotor)
MechanismMechanism External (inside) External (inside)
gear is shaft drivengear is shaft driven Internal gear is Internal gear is
driven by externaldriven by external Single tooth space Single tooth space
is displacedis displaced Design keeps Design keeps
tolerance close tolerance close throughout the cyclethroughout the cycle
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Gear PumpsGear Pumps(Internal Gear - Gerotor)(Internal Gear - Gerotor)
AdvantagesAdvantagesCheapCheapSimpleSimpleCheapCheap
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Gear PumpsGear Pumps(Internal Gear - Gerotor)(Internal Gear - Gerotor)
DisadvantagesDisadvantagesLimited pressure capabilityLimited pressure capabilityUnbalanced designUnbalanced designFixed displacementFixed displacementFrequently used as a charge pumpFrequently used as a charge pump
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Vane PumpsVane Pumps Pumping Pumping
mechanismmechanism
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Vane PumpsVane Pumps DisplacementDisplacement
VVDD = = ππ/2(D/2(Dcc-D-DRR)eL)eL C = CamC = Cam R = RotorR = Rotor E = eccentricityE = eccentricity L= depthL= depth
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Vane PumpsVane Pumps(Variations)(Variations)
Vane tip pressure control optionsVane tip pressure control optionsOutlet pressure under the vanesOutlet pressure under the vanesSurface pressure under the vanesSurface pressure under the vanes Intravanes: outlet pressure is applied always Intravanes: outlet pressure is applied always
to a small area of the vane while surface to a small area of the vane while surface pressure is applied to the rest of the areapressure is applied to the rest of the area
These are probably Vickers innovations These are probably Vickers innovations and hence are highlighted in the textand hence are highlighted in the text
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Vane PumpsVane Pumps(Variations)(Variations)
Balanced designsBalanced designs
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Vane PumpsVane PumpsAdvantagesAdvantages
Cartridges to quickly replace rotating groupCartridges to quickly replace rotating group
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Vane PumpsVane Pumps(Variations)(Variations)
Variable Displacement DesignVariable Displacement Design
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Vane PumpsVane PumpsAdvantagesAdvantages
Quieter than gear pumpsQuieter than gear pumpsHigher pressure capability than gear pumps?Higher pressure capability than gear pumps?Better volumetric efficiency than gear pumps?Better volumetric efficiency than gear pumps?Can be balanced in design for longer lifeCan be balanced in design for longer lifeVariable displacement an optionVariable displacement an option
DisadvantagesDisadvantagesMore complex and expensive than gear More complex and expensive than gear
pumpspumps
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Piston Pump DesignsPiston Pump Designs Axial PistonAxial Piston
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Piston Pump DesignsPiston Pump DesignsDisplacement of an axial piston pumpDisplacement of an axial piston pump
VVDD = YAD = YAD tan(tan(θθ))Y = Number of Pistons in the rotating groupY = Number of Pistons in the rotating groupA = the area of a single pistonA = the area of a single pistonD = is the diameter of the centerline circle of the D = is the diameter of the centerline circle of the
piston borespiston boresθθ is the angle of the swashplate or the bend angleis the angle of the swashplate or the bend angle
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Piston Pump DesignsPiston Pump Designs
Radial piston designRadial piston design
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Piston Pump DesignsPiston Pump Designs Bent axis designBent axis design
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Piston Pump DesignsPiston Pump Designs Bent axis – variable displacement designBent axis – variable displacement design
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Piston Pump DesignsPiston Pump Designs Axial piston – variable displacement designAxial piston – variable displacement design
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Piston Pump AdvantagesPiston Pump AdvantagesGenerally highest volumetric efficiencyGenerally highest volumetric efficiencyGenerally highest pressure capabilityGenerally highest pressure capabilityVariable displacement designsVariable displacement designs
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Piston Pump DisadvantagesPiston Pump DisadvantagesHigher cost (complexity)Higher cost (complexity)
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General IssuesGeneral IssuesPumps are not strictly continuous flow Pumps are not strictly continuous flow
devices. Discrete chambers are involved.devices. Discrete chambers are involved.Flow is collected for discharge through Flow is collected for discharge through
valve platesvalve platesDesign of the valve plate and the pump Design of the valve plate and the pump
mechanism affects pressure pulses and mechanism affects pressure pulses and variation (ripple) of torque and pressurevariation (ripple) of torque and pressure
Design of pumps is not taught hereDesign of pumps is not taught here
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General IssuesGeneral IssuesOur theoretical displacements can be used Our theoretical displacements can be used
to determine theoretical pump flowto determine theoretical pump flowActual flow is a linear function of pump Actual flow is a linear function of pump
displacement, speed, a units constant, and displacement, speed, a units constant, and an efficiency terman efficiency term
Two kinds of inefficienciesTwo kinds of inefficienciesVolumetric lossesVolumetric losses
Friction lossesFriction losses
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Actual Pump Output, QActual Pump Output, Q QQpp = (V = (Vpp n npp ηηVpp) /1000 where:) /1000 where: Q: L/minQ: L/min VVpp : cm : cm33/rev/rev ηVpp: Volumetric efficiency (decimal): Volumetric efficiency (decimal)
OR… OR… QQpp = (V = (Vpp n npp ηηVpp) /231 where:) /231 where: Q: GPMQ: GPM VVpp: in: in33/rev/rev ηηVpp: same as above (no units): same as above (no units)
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Torque to Drive a PumpTorque to Drive a Pump
TTpp = ( = (ΔΔP VP Vpp)/(2)/(2ππ ηηtptp) where:) where:TTpp : Newton meters torque required : Newton meters torque requiredΔΔP : pressure rise across the pump in MPaP : pressure rise across the pump in MPaVVp p : Pump displacement in cm: Pump displacement in cm33/rev/revηηtp tp : Pump torque efficiency – a decimal: Pump torque efficiency – a decimal
OR…OR…
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Torque to Drive a PumpTorque to Drive a PumpEnglish UnitsEnglish Units
TTpp = ( = (ΔΔP VP Vpp)/(2)/(2ππ ηηtptp) where:) where:TTpp : inch lbs torque required : inch lbs torque requiredΔΔP : pressure rise across the pump in PSIP : pressure rise across the pump in PSIVVp p : Pump displacement in inches: Pump displacement in inches33/rev/revηηtp tp : Pump torque efficiency – a decimal: Pump torque efficiency – a decimal
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Power to Drive the PumpPower to Drive the Pump
The hydraulic power is QThe hydraulic power is QppΔΔP/60 or P/60 or QQppΔΔP/1714 for SI and English unitsP/1714 for SI and English units (note this is (note this is actualactual pump flow, not theoretical) pump flow, not theoretical)
Shaft power to drive the pump is given by Shaft power to drive the pump is given by PPspsp = P = Phydrhydr / / ηηpppp where: where:ηηpppp = = ηηvpvp ηηtptp which is total pump efficiency which is total pump efficiency
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What Determines What Determines ηηvpvp & & ηηtptp ? ?
ηηvpvp is a function of clearance spaces, system is a function of clearance spaces, system pressure, and pump speedpressure, and pump speed
Leakage Leakage flowflow at a given pressure is relatively at a given pressure is relatively fixed regardless of pump speedfixed regardless of pump speed
It is also affected by fluid viscosity as lower It is also affected by fluid viscosity as lower viscosity fluid will result in higher leakage viscosity fluid will result in higher leakage flow and lower volumetric efficiencyflow and lower volumetric efficiency
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What about Torque Efficiency?What about Torque Efficiency?Torque efficiency is a function of speed Torque efficiency is a function of speed
and fluid viscosityand fluid viscosityHigher pump speeds will result in lower Higher pump speeds will result in lower
efficiency as viscous friction is speed efficiency as viscous friction is speed dependentdependent
Lower viscosity fluid can reduce viscous Lower viscosity fluid can reduce viscous losses but acts negatively on volumetric losses but acts negatively on volumetric efficiencyefficiency
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(μ n)/(ΔP x 1000)
Effic
ienc
ies
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Sizing PumpsSizing PumpsComponent sizing begins with the LOADComponent sizing begins with the LOAD
Load and actuator will determineLoad and actuator will determineFlow requirement for this circuitFlow requirement for this circuitPressure range required by the circuitPressure range required by the circuit(We’ll do this with cylinders and motors… soon)(We’ll do this with cylinders and motors… soon)
Total the simultaneous flow requirementsTotal the simultaneous flow requirementsSelect for the maximum load pressureSelect for the maximum load pressureAdd pressure drops that will occur in valves, Add pressure drops that will occur in valves,
lines and fittings ( another topic to come…)lines and fittings ( another topic to come…)
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Pump SizingPump SizingWith pump outlet pressure and flow known With pump outlet pressure and flow known
we will consider speed.we will consider speed. Industrial apps will use synchonous speed of Industrial apps will use synchonous speed of
electric motors. Generally 1750 rpm, or electric motors. Generally 1750 rpm, or possibly 1100. ($ decides)possibly 1100. ($ decides)
Small diesel apps such as skid loaders can Small diesel apps such as skid loaders can operate directly from engine crankshaft and operate directly from engine crankshaft and will have engine speed. (2000-3000 rpm).will have engine speed. (2000-3000 rpm).
Larger diesel apps – pump splitter with gear Larger diesel apps – pump splitter with gear reductions possible to optimize speedreductions possible to optimize speed
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Pump SizingPump SizingDetermine appropriate speed for your appDetermine appropriate speed for your appUse the equation for pump flow, solved for Use the equation for pump flow, solved for
displacementdisplacementVVpp = 1000Q/ = 1000Q/p p (n(npp ηηVpp))
What shall we use for What shall we use for ηηVpp????This is a function of speed, pressure, and fluid This is a function of speed, pressure, and fluid
viscosityviscosityLook for vendor data or curves and adjust…Look for vendor data or curves and adjust…
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Example Pump ProblemExample Pump ProblemCar CrusherCar Crusher
Need 125,000 lbs of forceNeed 125,000 lbs of force8 foot stroke8 foot stroke10 seconds to extend?10 seconds to extend?Target system max pressure of 1500 psiTarget system max pressure of 1500 psiWhat is the cylinder size needed?What is the cylinder size needed?
125,000 lbs/ A 125,000 lbs/ A (area)(area) = 1500 psi = 1500 psiArea = 83.33 inArea = 83.33 in22
ππrr22 = 83.33 in = 83.33 in2 2 r = 5.15 inches (let’s use 5”)r = 5.15 inches (let’s use 5”)
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Car Crusher Pump cont’dCar Crusher Pump cont’dWhat will the system pressure be?What will the system pressure be?
Cylinder area = 5Cylinder area = 522 ππ = 78.53 in = 78.53 in22
125,000 lbs / 78.53 in125,000 lbs / 78.53 in22 = 1592 psi = 1592 psi We study our plumbing and valves and allow We study our plumbing and valves and allow
for 300 psi drops in our systemfor 300 psi drops in our systemSet PRV to 1900?Set PRV to 1900?
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Car Crusher Pump cont’dCar Crusher Pump cont’dWhat is flow is required of the pump?What is flow is required of the pump?
Q = cyl stroke x area /timeQ = cyl stroke x area /timeQ = 96 in x 78.53 inQ = 96 in x 78.53 in22/ 10 sec = 754 in/ 10 sec = 754 in33/sec/sec754 in754 in33/sec x 1 gal/231 in/sec x 1 gal/231 in33 x 60 sec/min x 60 sec/minQ = 195.8 GPMQ = 195.8 GPM
Note that we have sized for one cylinder. We Note that we have sized for one cylinder. We might have others (a cylinder to kick your crushed might have others (a cylinder to kick your crushed Hummer bale out of the machine). Size for those Hummer bale out of the machine). Size for those that will be used simultaneouslythat will be used simultaneously..
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Car Crusher Pump cont’dCar Crusher Pump cont’dPump speed:Pump speed:
Electric power available? - 1750 rpmElectric power available? - 1750 rpmRemote from grid? Diesel at 2200 rpmRemote from grid? Diesel at 2200 rpm
Determine approximate sizeDetermine approximate sizeVVpp = 1000Q/ = 1000Q/p p (n(npp ηηVpp) or 231) or 231Q/Q/p p (n(npp ηηVpp))VVpp = 231*196/(1750*.95) = 231*196/(1750*.95)VVpp = 27.2 inches = 27.2 inches33/revolution/revolution
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Car Crusher Pump cont’dCar Crusher Pump cont’dLarge pump (27.2 inLarge pump (27.2 in33/rev)/rev)
Now we would look at vendorsNow we would look at vendorsFor this large, a piston design is likelyFor this large, a piston design is likelyCould also select two or more smaller pumps Could also select two or more smaller pumps
operating in tandem with outlets coupledoperating in tandem with outlets coupledSelection will be based upon costs of Selection will be based upon costs of
installation, costs of operation, and required installation, costs of operation, and required lifelifeContinuous use favors efficiencyContinuous use favors efficiencyIntermittent use may favor low initial costIntermittent use may favor low initial cost
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Pumps SelectionPumps SelectionFixed or variable displacement?Fixed or variable displacement?
So far our circuit is simple and we would likely So far our circuit is simple and we would likely use a fixed displacement pumpuse a fixed displacement pump
Later we will look at more efficient circuits and Later we will look at more efficient circuits and may wish to select a variable displacement may wish to select a variable displacement pump with appropriate controlspump with appropriate controls
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Reciprocating piston
External gear pump
Double screw pump
Sliding vane
Three-lobe pump (left)Double circumferential piston (centre)
Flexible tube squeegee(peristaltic)
Positive displacement pumps:
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Pumps in series and parallelPumps in series and parallel
Series
Parallel
Equivalent pump
Equivalent pump
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Pumps in Series
Add the heads (H) at each flow rate (Q)
For example, for two identical pumps the head will be double that of a single pump.
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Pumps in Parallel
Add the flow rates (Q) at each head (H)
For example, for two identical pumps the flow rate will be double that of a single pump.
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Pump-system operationPump-system operationSystem resistance (losses) curves
(typically H Q2)
C = operating point
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Positive Displacement Positive Displacement PumpsPumps
Typical Characteristics Typical Characteristics Constant Flow at Various PressuresConstant Flow at Various PressuresPulse Flow is possiblePulse Flow is possibleMost can pump solids suspended in liquidsMost can pump solids suspended in liquidsSelf-primingSelf-priming
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Types of PD PumpsTypes of PD Pumps
Rotary PumpsRotary Pumps Gear – Internal, ExternalGear – Internal, External LobeLobe VaneVane ScrewScrew
Reciprocating PumpsReciprocating Pumps PistonPiston PlungerPlunger DiaphragmDiaphragm
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Rotary vs. Reciprocating Rotary vs. Reciprocating PumpsPumps
Rotary pumps transfer liquid through the Rotary pumps transfer liquid through the action of a rotating mechanism (gear, lobe action of a rotating mechanism (gear, lobe or vane) operating inside a rigid containeror vane) operating inside a rigid container
Pumping rates varied by changing speed Pumping rates varied by changing speed of rotorof rotor
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Rotary vs. Reciprocating Rotary vs. Reciprocating Pumps Pumps
Reciprocating pumps Reciprocating pumps move liquids by move liquids by changing the internal changing the internal volume of the pumpvolume of the pump
Require valves on the Require valves on the suction and discharge suction and discharge sidessides
Pumping rates varied Pumping rates varied by changing the by changing the frequency or the stroke frequency or the stroke lengthlength
Source: http://www.watson-marlow.com/wna-se/p-fmi.htm
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Internal Gear PumpsInternal Gear Pumps
•Smaller gear rotating within a bigger gear
•Partial vacuum created by meshing and unmeshing of internal teeth with external teeth
•Crescent divides liquid flow between rotor and idler gears
Source: http://www.pumpschool.com/principles/internal.htm
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PD Pump CurvePD Pump Curve
Source: http://www.driedger.ca/ce2_pdp/CE2_PDP.html