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PEMP MMD2516
Introduction to Fluid Power System
Session Speaker:Arup Bhattacharya
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Session Objectives
At the end of this session the delegate would have understood
The meaning of fluid power
Classification of power systems
Drives, control and actuation in a power system
Comparison of different power systems
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Session Topics
Fluid power Introduction
Introduction to power systems: Mechanical, Electrical, Hydraulic, Pneumatic,
Hydrodynamic, Hydrostatic
Application of fluid power in industry application.
Energy transmission
Analogy between different power circuits
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Fluid Power
Technology that deals with the generation, control and transmission of power
using pressurized fluids (either liquids or gases)
The force and motion may be in the form of pushing, pulling, rotating,
regulating or driving
Fluid power is called hydraulics when the fluid is a liquid and is called
pneumatics when the fluid is a gas
First hydraulic fluid used was water but usage is reduced due to many
disadvantages
Various types of oils are used these days
Pneumatic systems uses extensively air
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History of Fluid Power
Fluid power technology began in 1650 with the discovery of Pascals Law:
Pressure is transmitted undiminished in a confined body of fluid
In 1738, Bernoulli developed his law of conservation of energy for a fluid
flowing in pipe
After Industrial Revolution of 1850 in Great Britain these laws were applied to
industry
By 1870, fluid power was extensively used to drive hydraulic equipments such
as cranes, presses, winches, extruding machines, hydraulic jacks, shearing
machines and riveting machines
Then in 19th century electricity emerged as a dominant technology which
shifted the effort from fluid power to electric power
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History (cont.)
High pressure fluid power systems were put into practical application in 1925
when Harry Vickers developed the balanced vane pump
Today fluid power has become an inevitable part of industry
Applications of FP are in automobiles, tractors, airplanes, missiles, boats, robots
and machine tools
In automobile the applications include hydraulic and pneumatic brakes,
automotive transmissions, power steering, power brakes, air-conditioning,
lubrication, water coolant and gasoline pumping system
In modern technology hydraulic combines with electronics called electro -
hydraulic systems are used
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Most Powerful Hydraulic System
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How is this figure
related to this
module
1. God created the first and most powerful
hydraulic system
2. It is a double pump delivering a fluid flow rate
of about 10L/min at 0.16 bar maximum pressure
3. The pump feeds a piping network stretching
more than 1,00,000 km
4. It is human blood circulatory system
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Power System
Power systems are used to transmit and control power
This function is shown as below:
Rotary Motion ( and T)
Input Power Output Power
Linear Motion (V and F)
The basic parts of a power systems are:
1. Source of energy delivering mechanical power
2. Energy transmission, transformation and control elements
3. Load requiring mechanical power of either rotary or linear motion.
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Powertransmission,
transformationand
control(Mechanical/
Electrical/Liquids/
CompressedAir)
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Classification of Power System
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Power System
ElectricalMechanical Fluid
PneumaticHydraulic
Hydrodynamics(Hydrokinetics)
Hydrostatics
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Mechanical Power System
Uses mechanical elements totransmit and control
mechanical power
Advantages compared to
other power systems: Relatively simple
construction
Easy maintenance
Smooth operation Low cost
Disadvantages include:
Minimal power to wt. ratio
Limitation of the powertransmission distance
Poor flexibility andcontrollability
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An Automotive Drive Train
The gear box (3) is connected to the engine (1)through the clutch (2)The input shaft of the gear box turns at the samespeed as the engine
The output shaft (4) turns at different speeds,depending on the selected gear transmission ratioThe power is then transmitted to the wheels (8)through the universal joints (5), drive shaft (6) anddifferential (7)
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Electrical Power System
Advantages:
High flexibility and a very long power transmission distance
Disadvantages: Produce mainly rotary motion
Rectilinear motion of high power can be obtained by converting therotary motion using a suitable gear system or by using drum and wire
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Electrical System - Example
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Hydrostatic Power System
Power is transmitted by increasing the pressure energy of theliquid
Widely used in industry, mobile equipment, aircrafts, ship controland others
These are commonly called hydraulic power system
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Example
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Hydrodynamic Power Systems
Also called Hydrokinetic Power Systems
Transmit power by increasing mainly the Kinetic Energy of the liquid
Generally consists of a rotodynamic pump, a turbine and additional control
elements
Applications limited to rotary motion
Replace classical mechanical system due to:
High power to weight ratio
Better controllability
Two main types of hydrodynamic power systems:
Hydraulic Coupling
Torque Convertor
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Hydraulic Coupling
Essential fluid based clutch
Consists of a pump (2), driven by an input
shaft (1) and a turbine (3), coupled to the
output shaft (4)
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Working Principle
When the pump impeller rotates, the oil flows
to the turbine at high speed. The oil then impacts the turbine blades, where it loses
most of the kinetic energy it gained from the pump. The oil re-circulates in a closed
path inside the coupling and the power is transmitted from the input shaft to the output
shaft. The input torque is practically equal to the output torque.
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Torque Convertor
Is a hydraulic coupling with one extra
component: the stator, also called the
reactor (5)
The stator consists of a series of guide
blades attached to the housing
The torque converters are used where
it is necessary to control the output torque and develop a transmission ratio, other
than unity, keeping acceptable transmission efficiency
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Basic Pneumatic Power System
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The air compressor converts the mechanical energy of the prime mover into mainly pressure
energy of compressed air. This transformation facilitates the transmission and control of power. An
air preparation process is needed to prepare the compressed air for use. The air preparation
includes filtration, drying, and the adding of lubricating oil mist. The compressed air is stored in the
compressed air reservoirs and transmitted through rigid and/or flexible lines. The pneumatic power
is controlled by means of a set of pressure, flow, and directional control valves. Then, it is
converted to the required mechanical power by means of pneumatic cylinders and motors
(expanders)
Use compressed air
as a working medium
for the power
transmission
Principle of operation
is similar to electrical
power systems
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Example
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Fluid Power Applications
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McKibben Air Muscles
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Fluid Power Applications
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Application of FPC is space shuttle
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FP Applications in Landing Gear
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Fluid Power Applications
PositionControl
Industrialmachineryandequipment
Aerospace
ManufacturingIndustrialApplication
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Advantages of Fluid Power
Ease and accuracy of control
Multiplication of force
Constant force or torque
Simplicity, safety, economy
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Power systems comparison
SystemProperties
Mechanical Electrical Pneumatic Hydraulic
Inputenergysource ICEandelectricmotor
ICEandhydraulic,
airorsteam
turbines
ICE,electric
Motorand
Pressuretank
ICE,electric
motor and
accumulators
Energy transferelement
Mechanicalparts,
levers,shafts,gearsElectricalcables
andMagneticfieldPipesandhoses Pipesandhoses
Energycarrier Rigidand elasticobjects
Flowofelectrons Air Hydraulicfluids
Powertoweightratio
Poor Fair Best Best
Torque/ Inertia Poor Fair Good Best
Response speed Fair Best Fair Good
Control(acceleration)
Fair Best Good Verygood
Dirtsensitivity Best Best Fair FairRelativecost Best Best Good FairMotiontype Mainlyrotary Mainlyrotary Linearorrotary Linearorrotary
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Parameter comparison
Typeofpowersystem
Effort Flow PowerVariable Unit Variable Unit Variable Unit
Mechanical
(linear)
Force(F) N Velocity (v) m/s P=Fv W
Mechanical
(rotary)
Torque(T) Nm Angularspeed
()
rad/s P=T W
Electrical
(DC)
Electric
Potential, (V/e)
V Electriccurrent
(i)
A P=Vi W
Hydraulic Pressure (p) Pa FlowRate(Q) P=pQ W
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Different Forms of Pressure Measurement
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Energy conversion example Load lifting by a Forklift
Consider a forklift that lifts a
load vertically for a distance
y in time t
The vertical force needed to lift
the load = F = mg
Where m = mass to be lifted and g = acceleration due to gravity
Work done by the forklift in time t = W = Fy = mgy (assuming no friction)
The mechanical power delivered to the load = W/ t
= mgy/ t
= F.v
Assuming that the load lifting is to be done by a hydraulic cylinder.
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This cylinder acts on the lifted body by a force F and drives it with a speed v.
It is a single acting cylinder which extends by the pressure force
and retracts by the body weight.
The pressurized oil flows to the hydraulic cylinder at a flow rate
Q and its pressure isp
Assuming no friction the pressure force needed to extend the
piston = F = p Ap
In timet the piston moves y, hence volume of oil entering = V = Ap y
The oil flow rate entering the cylinder = Q = V/ t = Ap y/ t = Ap v
The inlet to the cylinder assuming ideal cylinder = F.v = p Ap .v = pAp . Q/Ap
= pQ (v = Q/Ap)
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