Day 1c - Hydraulic Fluids and Fluid Properties

PEMP – PEMP – MMD 2516

Introduction to Fluid Power System Session Speaker: Arup Bhattacharya

Session Objectives


At the end of this session the delegate would have understood

• The meaning of fluid power • Clas Classi sifi fica cati tion on of powe powerr syst system emss • Drives, control and actuation in a power system • Comp Compar aris ison on of dif differe ferent nt powe powerr syst system emss

© M S Ramaiah School of Advanced of Advanced Studies – Studies – Bangalore

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Session Objectives


At the end of this session the delegate would have understood

• The meaning of fluid power • Clas Classi sifi fica cati tion on of powe powerr syst system emss • Drives, control and actuation in a power system • Comp Compar aris ison on of dif differe ferent nt powe powerr syst system emss


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Session Topics


• Flui Fluid d pow power – Intr Introd oduc ucti tion on • Introduction to power systems: Mechanical, Electrical, Hydraulic, Pneumatic, Hydrodynam Hydrodynamic, ic, Hydrostati Hydrostaticc

• Appl Applic icaation tion of flui fluid d pow power in indu indust stry ry appli ppliccation tion.. • Energ Energy y transm transmiss ission ion • Anal Analog ogy y betw betwee een n dif differe ferent nt powe powerr circ circui uits ts


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Fluid Power

PEMP – MMD 2516

• 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

© M S Ramaiah School of Advanced Studies – Bangalore

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History of Fluid Power

PEMP – MMD 2516

• Fluid power technology began in 1650 with the discovery of Pascal’s 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.)

PEMP – MMD 2516

• The modern era of fluid power is considered to have begun in 1906, when a hydraulic system was developed to replace electrical systems for elevating controlling guns on the battleship USS Virginia

• In 1926, the United States developed the first utilized, packaged hydraulic system consisting of a pump, controls and actuators

• The military and naval industry had used fluid power for cargo handling, winches, propeller pitch control, submarine control systems, operation of shipboard aircraft elevations and drive systems for radar and sonar

• During world war II aviation and aerospace industry provided impetus for many fluid power technology like hydraulic actuated landing gears, cargo doors, gun drives and flight control devices like rudders, ailerons and elevons for aircrafts


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History (cont.)

PEMP – MMD 2516

• 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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PEMP – MMD 2516

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 © M S Ramaiah School of Advanced Studies – Bangalore

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PEMP – MMD 2516

Power System • Power systems are used to transmit and control power • This function is shown as below:

Rotary Motion (ω and T)

Input Power

Power transmission, transformation and control (Mechanical/ Electrical/ Liquids/ Compressed Air)

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. © M S Ramaiah School of Advanced Studies – Bangalore

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Classification of Power System

PEMP – MMD 2516

Power System

Mechanical

Electrical

Fluid

Hydraulic

Hydrodynamics (Hydrokinetics)


Pneumatic

Hydrostatics

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Mechanical Power System

PEMP – MMD 2516

• Uses mechanical elements to transmit and control mechanical power

• Advantages compared to other power systems: – Relatively simple construction 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 same speed as the engine •The output shaft (4) turns at different speeds, depending on the selected gear transmission ratio •The power is then transmitted to the wheels (8) through the universal joints (5), drive shaft (6) and differential (7)

– Easy maintenance – Smooth operation – Low cost

• Disadvantages include: – Minimal power to wt. ratio – Limitation of the power transmission distance

– Poor flexibility and controllability


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Electrical Power System

PEMP – MMD 2516

• 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 the rotary motion using a suitable gear system or by using drum and wire © M S Ramaiah School of Advanced Studies – Bangalore

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Electrical System - Example


PEMP – MMD 2516

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Hydrostatic Power System

PEMP – MMD 2516

• Power is transmitted by increasing the pressure energy of the liquid

• Widely used in industry, mobile equipment, aircrafts, ship control and others

• These are commonly called hydraulic power system © M S Ramaiah School of Advanced Studies – Bangalore

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Example


PEMP – MMD 2516

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Hydrodynamic Power Systems

PEMP – MMD 2516

• 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 © M S Ramaiah School of Advanced Studies – Bangalore

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Hydraulic Coupling

PEMP – MMD 2516

• 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

PEMP – MMD 2516

• 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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PEMP – MMD 2516

Basic Pneumatic Power System

•Use compressed air as a working medium for the power transmission •Principle of operation is similar to electrical power systems 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) © M S Ramaiah School of Advanced Studies – Bangalore

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Example


PEMP – MMD 2516

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Fluid Power Applications

PEMP – MMD 2516

McKibben Air Muscles © M S Ramaiah School of Advanced Studies – Bangalore

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PEMP – MMD 2516

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PEMP – MMD 2516

Application of FPC is space shuttle


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PEMP – MMD 2516

FP Applications in Landing Gear


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PEMP – MMD 2516

Aerospace

Industrial machinery and equipment

Position Control

Manufacturing

Industrial Application


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Advantages of Fluid Power

PEMP – MMD 2516

• Ease and accuracy of control • Multiplication of force • Constant force or torque • Simplicity, safety, economy


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Power systems comparison System Properties

Mechanical

Electrical

Pneumatic

PEMP – MMD 2516

Hydraulic

Input energy source

ICE and electric motor

ICE and hydraulic, air or steam turbines

ICE, electric Motor and Pressure tank

ICE, electric motor and accumulators

Energy transfer element

Mechanical parts, levers, shafts, gears

Electrical cables and Magnetic field

Pipes and hoses

Pipes and hoses

Energy carrier

Rigid and elastic objects

Flow of electrons

Air

Hydraulic fluids

Power to weight ratio

Poor

Fair

Best

Best

Torque/ Inertia

Poor

Fair

Good

Best

Response speed

Fair

Best

Fair

Good

Control (acceleration)

Fair

Best

Good

Very good

Dirt sensitivity

Best

Best

Fair

Fair

Relative cost

Best

Best

Good

Fair

Motion type

Mainly rotary

Mainly rotary

Linear or rotary

Linear or rotary


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PEMP – MMD 2516

Parameter comparison Type of power system

Effort Variable

Flow Unit

Power

Variable

Unit

Variable

Unit

Mechanical (linear)

Force (F)

N

Velocity (v)

m/s

P = Fv

W

Mechanical (rotary)

Torque (T)

Nm

Angular speed (ω)

rad/s

P = Tω

W

Electrical (DC)

Electric Potential, (V/e)

V

Electric current A (i)

P = Vi

W

Hydraulic

Pressure (p)

Pa

Flow Rate (Q)

P = pQ

W


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PEMP – MMD 2516

Different Forms of Pressure Measurement


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PEMP – MMD 2516

Energy conversion example – Load lifting by a Forklift • Consider a forklift that lifts a load vertically for a distance ‘y’ in time ‘Δt’

• 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 Δt = W = Fy = mgy (assuming no friction) • The mechanical power delivered to the load = W/ Δt = mgy/ Δt = F.v

Assuming that the load lifting is to be done by a hydraulic cylinder. © M S Ramaiah School of Advanced Studies – Bangalore

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PEMP – MMD 2516

• 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 is p

• Assuming no friction the pressure force needed to extend the piston = F = p Ap

• In time Δt the piston moves y, hence volume of oil entering = V = Ap y • The oil flow rate entering the cylinder = Q = V/ Δt = Ap y/ Δt = Ap v • The inlet to the cylinder assuming ideal cylinder = F.v = p Ap .v = pAp . Q/Ap = pQ © M S Ramaiah School of Advanced Studies – Bangalore

(v = Q/A p) 31

Day 1c - Hydraulic Fluids and Fluid Properties

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