Hydraulics

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Hydraulics Pneumatics Technology

• DMM3623

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What is Fluid Power ?

• Technology that deals with generation, control
  and transmission of power, using pressurized
  fluids
• example brake automobile, launches spacecraft,
  mines coal, drives machine tools even drills
  teeth.
• Hydraulics when the fluid is liquid
• - petroleum oils, synthetic oils and water.
• Pneumatics when the fluid is gas
• - air (very abundant and can be readily
  exhausted into the atmosphere after completing
  task)

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Hydraulics
Hydraulic Basics Hydraulics is the science of
transmitting force and/or motion through the
medium of a confined liquid. In a hydraulic
device, power is transmitted by pushing on a
confined liquid. The transfer of energy takes
place because a quantity of liquid is subject to
pressure. To operate liquid-powered systems, the
operator should have a knowledge of the basic
nature of liquids. This chapter covers the
properties of liquids and how they act under
different conditions.
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Fluid System
Fluid transport Delivery of a fluid from one
location to another to accomplish some useful
purpose.
Fluid power Designed specifically to perform
work. Work-accomplished by a pressurized fluid
bearing directly on an operating fluid cylinder
or fluid motor. Fluid cylinder-produces a force
in linear motion. Fluid motor-produces a torque
in rotary motion.
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EXAMPLES
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Advantages of using Hydraulics

1. Very high force despite small components (if
   pneumatics, bigger components are needed for high
   force, thus, incur high cost as well as wastage
   of compressed air)
2. Very slow and linear movements (if pneumatics,
   too slow will create jerking on the cylinder)
3. Very exact positioning (stops exactly on a
   point). Compared to pneumatics, theres a
   tolerance and if a load is given, it will move a
   little.

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Advantages of using Hydraulics

• Start-up under heavy loads (Possible to start the
  motor process a job with a load attached to it.
  This is because there is oil in the actuator
  though the pump is idling).
• Simplicity, safety, economy
• In general, fluid power systems use fewer moving
  parts than comparable mechanical or electrical
  systems. Thus, they are simpler to maintain and
  operate. This, in turn, maximizes safety,
  compactness and reliability.

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Disadvantages of using Hydraulics

• Slow movement of actuators (Pneumatics are
  faster)
• Messy (Leakage may occur and if not bothered, the
  surrounding area could be messy. However,
  constant cleaning could avoid messy.)
• Dangerous!
• i. It produces extreme pressure and if theres a
  leakage, oil will be forced out. Stopping the
  flow with bare hand would result in a punctuated
  wound.
• ii. While in process, oil became hot and
  flammable (though not easily happened).
  Therefore, it is advisable to control the
  temperature by limiting it (turning off the
  machine if the limit is exceeded).

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General Application of Hydraulics
Stationary Hydraulics
Mobile Hydraulics

• Using manual hydraulics to control
• Crane
• Excavator
• Back-hoe

• Using electro-hydraulics to control
• Press machine
• Molding machine
• Lathe machine

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4 hydraulic cylinders
stick
boom
bucket
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Sky tram is unique. It is self-propelled and
travels on a stationary cable. Because the tram
moves instead of the cable, the operator can
stop, start, and reverse any one car completely
independently of any other car in the tram
system. Integral to the design of the Sky-tram
drive is a pump (driven by a standard
eight-cylinder gasoline engine) which supplies
pressurized fluid to four hydraulic motors.
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Tilt Cylinders - are hydraulic cylinders that are
mounted to the truck frame and the mast. The tilt
cylinders pivot the mast to assist in engaging a
load. The Mast - is the vertical assembly that
does the work of raising and lowering the load.
It is made up of interlocking rails that also
provide lateral stability. The interlocking rails
may either have rollers or bushings as guides.
The mast is either hydraulically operated by one
or more hydraulic cylinders or it may be chain
operated with a hydraulic motor providing motive
power. It may be mounted to the front axle or the
frame of the forklift.
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Common Fluid in Hydraulic System

• Base stock may be either castor oil, glycol,
  ester, ethers, mineral oil, chutte etc.
• Some of the trade names for hydraulics fluids
  include
• Durad
• Fyrquel
• Houghton-Safe
• lubritherin

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Fluid Selection

• A hydraulic fluid has the following 4 primary
  functions-
• Transmit power
• Lubricate moving parts
• Seal clearance between mating parts
• Dissipate heat

• In addition a hydraulic fluid must be inexpensive
  and readily available. A hydraulic fluid should
  have the following properties-
• Good lubricity
• Ideal viscosity
• Chemical stability
• Fire resistance
• Low density
• Foam resistance
• Nontoxicity
• Low volatility

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Physical differences between liquids and gases
Parameter Liquid Gas Volume Has its own
volume Volume is determined by
container Shape Takes shape of
container Expands to completely but only to
its volume fill and take the shape of the
container Compressibility Incompressible for
most Readily compressible engineering
applications
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Pressure
Pressure is force exerted against a specific area
(force per unit area) expressed in pounds per
square inch (psi). Pressure can cause an
expansion, or resistance to compression, of a
fluid that is being squeezed. A fluid is any
liquid or gas (vapor). Force is anything that
tends to produce or modify (push or pull) motion
and is expressed in pounds.
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Force
Pressure is defined as force per unit area.
Hence, pressure is the amount of force acting
over a unit area, as indicated by
Pressure (P) Force (F) / Area (A)
Example of P at 100 kPa and A at 20 m², F P x
A, so F 100 kPa x 20 m² F 2000 kN.
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Flow
Flow Flow is the movement of a hydraulic fluid
caused by a difference in the pressure at two
points. In a hydraulic system, flow is usually
produced by the action of a hydraulic pump-a
device used to continuously push on a hydraulic
fluid. The two ways of measuring flow are
velocity and flow rate. a. Velocity. Velocity
is the average speed at which a fluid's
particles move past a given point, measured in
feet per second (fps). Velocity is an important
consideration in sizing the hydraulic lines that
carry a fluid between the components. b. Flow
Rate. Flow rate is the measure of how much
volume of a liquid passes a point in a given
time. Flow rate determines the speed at which a
load moves and, therefore, is important when
considering power.
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Energy
Energy is the ability to do work. The three forms
of energy are potential, kinetic, and heat. Work
measures accomplishments it requires motion to
make a force do work. Power is the rate of doing
work or the rate of energy transfer.
a. Potential Energy. Potential energy is energy
due to position. An object has potential energy
in proportion to its vertical distance above the
earth's surface. For example, water held back by
a dam represents potential energy because until
it is released, the water does not work. In
hydraulics, potential energy is a static factor.
When force is applied to a confined liquid, as
shown in Figure 1-4, potential energy is present
because of the static pressure of the liquid.
Potential energy of a moving liquid can be
reduced by the heat energy released. Potential
energy can also be reduced in a moving liquid
when it transforms into kinetic energy. A moving
liquid can, therefore, perform work as a result
of its static pressure and its momentum.
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Example

• A lifting is to lift a load of 15kN and is to
  have a system pressure of 75 bar. How large does
  the piston surface need to be?
• Solution
• P F/A
• A F/P
• 15000N/(75x105 Pa)
• 0.002 m2

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EXAMPLE

F210 kN d23 m d10.5 m S20.5m F1 ? S1 ?
S1

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Answer

• F1/A1 F2/A2
• A1 0.1963 m2 (1 mark)
• A2 7.0686 m2 (1 mark)
• F1 (F2/A2) x A1
• (10 kN / 7.0686 m2) x 0.1963 m2
• 0.278 kN (3 marks)

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Answer

• W F.s
• F1s1 F2s2
• 0.278 x s1 10 x 0.5
• s1 17.986 m (5 marks)

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