Fluid Power Application - Introduction

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Fluid Power Application

Hydraulics & Pneumatics KMD 3133

By,Mohd Darnalis A.Rahman

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What is Fluid Power?

Deals with the generation, control, and transmission of power using pressurized fluids.The muscle that moves industry. Most modern machines driven by it.Applications,

fluid power steering & brakes automobiles, drives machine tools, controls airplanes, moves earth (excavation), even drills teeth.

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Fluid Transport? or Fluid Power?

Should be realized that there are actually 2(two) different types of fluid systems.

1. Fluid transportSole objective is to deliver a fluid from one location to another to accomplish some useful purpose.

2. Fluid powerDesigned specifically to perform work.

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Fluid Power

The work is accomplished by a pressurized fluid acting on a fluid cylinder or fluid motor.

A fluid cylinder produces a force.A fluid motor produces a torque.Fluid cylinders & motors provide the muscle to do desired work.

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Fluid Power - History

Known as hydraulics & pneumatics due to the working fluid can either be liquid or gas.Working on the Pascal’s Law

“Pressure is transmitted undiminished in a confined body of fluid”Pascal found that when he rammed a cork into a jug completely full of wine, the bottom of the jug broke and fell out.

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Pascal’s law indicated that the pressures were equalat the top and bottom of the jug, however, the jug has a small opening area at the top and a large area at the bottom, thus the bottom absorbs greater forcedue to its larger area.

Pressure

Pressure Transmitted

Acting Area 2

Acting Area 1

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While Bernoulli developed his law of conservation of energy for a fluid flowing in a pipeline.Pascal’s & Bernoulli’s law is the working principle of all fluid power applications and are used for analysis purposes.

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Fluid Power – Hydraulics

Hydraulics SystemsUses liquids such as mineral oils, water, synthetic oils, even molten metals.Water was the 1st hydraulic fluids

Not very suitable due to several deficiencies, such as freezes, poor lubricant & corrosive characteristics.

Oils are superior and widely used.Liquids provides very rigid medium (uncompressible) for transmitting power & thus provides huge forces moving loads (with accuracy & precision)

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Fluid Power – Pneumatics

Pneumatics SystemsUses air as the gas medium due to abundantsupply and can be readily exhausted to the atmosphere.Other gasses are not favorable due to cost, efficiency reasons but might be considered for special/critical purposes, should there be.Gas exhibits spongy characteristics due to compressibility of gas.However it is less expensive to build, operate& maintained.

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Applications

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Applications

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Advantages of Fluid Power

3 basic methods of transmitting power;ElectricalMechanicalFluid Power

Efficient overall system – using combination of all above.Fluid systems can transmit power more economically over greater distance than mechanical system. However, restricted to shorter distances compared to electricalsystems

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Fluid power secret is its versatility and manageability.Not constrain to the physical geometry of the machine compared to mechanical systems. E.g. automotive braking systems.Power transmitted in almost limitlessquantities. Not constrained by the physical limitation of materials such in an electrical systems. (E.g. Electromagnets, depends on saturation limit of steel)

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Main advantages of Fluid Power systems are:1. Ease and accuracy of control.2. Multiplication of force.3. Constant force or torque.4. Simplicity, safety & economy.

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Drawbacks of Fluid Power

In spite of all highly desirable of fluid power, it is not the answer of all power transmission problems.

Hydraulics oil are messy.Leakage is virtually impossible to eliminate completely.Safety issue – hydraulics lines might burst resulting to injuries if proper design are not implemented.

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Applications of Fluid Power

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Pneumatic powered Dextrous articulated artificial limb

Courtesy of ,

Shadow Robot Company

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Pneumatic powered artificial muscle. Air Muscle, Courtesy of Shadow Robot Company

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Components of a Fluid Power System (Hydraulic System)

There are 6(six) basic components1. Tank (reservoir) – holding the liquid (hydraulic oil).2. Pump – forcing liquid through the system.3. Electric motor or other power source to drive the

pump.4. Valves – controlling liquid direction, pressure & flow

rate.5. Actuators – convert energy of liquid into mechanical

force / torque providing useful work.Cylinders – linear motions.Motors – rotary motions.

6. Piping – Carries the liquid from one location to another.

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Figure 1-21

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Figure 1-20

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Complexity of hydraulic systems will vary depending on the specific applicationsEach unit is a complete, packaged power system containing,

Electric motorPumpShaft couplingReservoir (oil tank)Miscellaneous piping, pressure valves and Other components as required for proper operation such as pressure gages.

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Figure 1-22

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Components of a Fluid Power System (Pneumatic System)

There are also 6(six) basic components1. Air Tank (reservoir) – storing a given volume of

compressed air.2. Compressor – Compresses air from the atmosphere.3. Electric motor or other prime mover to drive the

compressor.4. Valves – controlling liquid direction, pressure & flow

rate.5. Actuators – convert energy of liquid into mechanical

force / torque providing useful work.Cylinders – linear motions.Motors – rotary motions.

6. Piping – distribute the pressurized air from one location to another.

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Fig 1-23

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Complexity of pneumatic systems will vary depending on the specific applications.Self-contained pneumatic power unit is consist of,

Electric motorCompressorShaft couplingReservoir (Air tank)Miscellaneous piping, pressure valves and Other components as required for proper operation such as pressure gages.

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Should be noted;In pneumatic systems after pressurized air is spent driving actuators, it is then exhaustedback to the atmosphere.

While,In hydraulic systems, the spent oil drains back to the reservoir and is repeatedly reused after being re-pressurized & filtered by the system.

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Closed-Loop vs. Open Loop System

Fluid power can either be using the closed-loop or open-loop type.

Closed-loop SystemUsing feedback.Output from system is automatically sampled and compared (fed back) to the input / command signal by means of a device known as feedback transducer.If there is significance difference between command signal and feedback signals, action will be taken automatically to correct the system output.A.K.A servo systemsservo systems, valves used to direct fluid are typically called servo valves.

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Open-loop SystemNot using feedback.Performance solely depends on individual components and how they interact in the circuit.No input / output compensation occur.Most hydraulic circuits are of the open-loop type, which generally not so complex / precise as closed-loop.Errors due to slippage (oil leakage which somehow depends on the pressure & temperature.)Example,

Leakage past seals inside pumps due to viscosity change of fluid which affected to the rise of operating temperature.Leading to pressure and speed of actuators to drop.

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Fluid Power Application - Introduction

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