day 1c - hydraulic fluids and fluid properties

7/29/2019 Day 1c - Hydraulic Fluids and Fluid Properties

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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

MSRamaiah SchoolofAdvancedStudies Bangalore 2


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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

MSRamaiahSchoolofAdvancedStudies Bangalore 3


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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


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.


Powertransmission,

transformationand

control(Mechanical/

Electrical/Liquids/

CompressedAir)


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Classification of Power System


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


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)


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


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


McKibben Air Muscles


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Application of FPC is space shuttle



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FP Applications in Landing Gear



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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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MSRamaiahSchoolofAdvancedStudies Bangalore CenterforMachineryDesign 32

day 1c - hydraulic fluids and fluid properties

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