Download Chapter 3 Basic Physical Principles

1/28/2010
Chapter 3
Basic Physical Principles
Applications to Fluid Power
Systems
y
1
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Objectives
 Identify and explain the design and operation of
th six
the
i basic
b i machines.
hi
 Describe the factors that affect energy in fluid
power systems.
 Explain how the potential power of a fluid
power system is established
established.
 Describe the nature of heat and how it is
measured in fluid power systems.
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Objectives
 Explain the nature of electricity and the basic
methods
th d usedd for
f electrical
l t i l measurement.
t
 Identify and explain the operation of basic
electrical circuits.
 Name and describe the characteristics
associated with the fluids used in fluid power
systems.
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Simple Machines
 Millions of designs of complex machines exist
i our society
in
i t today.
t d
Brand X
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Simple Machines
 However, there are only six basic types of
machines:
hi
–
–
–
–
–
–
Lever
Inclined plane
Wedge
Screw
Pulley
Wheel and axle
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Simple Machines
 Levers
– First-class lever
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Simple Machines
 Levers
– Second-class lever
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Simple Machines
 Levers
– Third-class lever
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Simple Machines
 Inclined plane
 Wedge
Photo courtesy of handiramp.com
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Simple Machines
 Screw
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Simple Machines
 Pulley
Dynamic Graphics
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Simple Machines
 Wheel and axle
Creatas
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Basic Principles of
Mechanics
 Energy is the capacity to do work
– Potential energy is stored energy
– Kinetic energy which is energy in motion
 Force is the overall effort needed to produce,
change, or stop motion
 Pressure is force exerted over a unit area
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Mechanical
Measurements
 Torque is a turning or twisting force applied to
a shaft
h ft
– Designated in pound-feet or pound-inches
 Work is the application of force through a
distance
– Designated in foot
foot-pounds
pounds or horsepower
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Mechanical
Measurements
 Power is the rate at which work is performed
– Designated in foot-pounds per minute
 Mechanical advantage is a relationship between
the effort put into a machine and the resistance
overcome
– Calculated using either the forces or distances
involved
– Expressed as a numeric ratio
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Mechanical
Measurements
 Mechanical efficiency is a comparison of the
workk input
i
t andd workk output
t t off a machine
hi
– Calculated by dividing the workput of the machine
by the work input
– Expressed as a percentage
– Always
y less than 100% due to losses
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Principles of Heat
Transfer
 Thermodynamics is the science dealing with the
properties
ti off matter
tt related
l t d to
t heat
h t andd the
th
conversion of energy from one form to another
 Heat is kinetic energy
– Measured in British thermal units (Btu) or calories
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Principles of Heat
Transfer
 Heat is generated in a fluid power system
whenever a pressure drop occurs that does
not produce work
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Principles of Heat
Transfer
 Temperature is determined by the rate of
molecular
l l movementt within
ithi a substance
bt
 Temperature is measured in degrees
– Fahrenheit scale (United States)
– Celsius scale (everywhere else)
– Rankine and Kelvin scales (often used for
scientific and engineering calculations)
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Principles of Heat
Transfer
 Sensible heat can be measured by a thermometer
– Felt as “hot” or “cold”
 Latent heat is the heat needed to change the state
of a substance without changing its temperature
– Ice to water
– Water to steam
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Principles of Heat
Transfer
 Heat may be moved using three modes of
t
transfer:
f
– Conduction
– Convection
– Radiation
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Principles of Heat
Transfer
 Conduction involves molecular activity in
solids
lid
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Principles of Heat
Transfer
 Convection uses physical currents in gases or
li id
liquids
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Principles of Heat
Transfer
 Radiation transfers heat by the use of
electromagnetic
l t
ti waves
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Electricity and Magnetism
 An atom is the smallest identifiable part of an
element
l
t
 Composed of:
– Electrons (–)
– Protons (+)
– Neutrons (no charge)
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Electricity and Magnetism
 Electrical flow occurs
when electrons leave the
outer orbital paths and
move other free
electrons through the
substance with them
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Electricity and Magnetism
 Magnetism is the ability of a material to attract
iron
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Electricity and Magnetism
 Electrical current can be used to magnetize iron
andd iron
i
alloys
ll
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Electricity and Magnetism
 Electricity may be produced using the lines of
f
force
th
thatt surroundd a magnett
– When an electrical conductor cuts these magnetic
lines of force, electricity is produced
– Electrical output is dependent on the number of
lines cut and the speed with which they are cut
– This is called electromagnetic induction
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Electricity and Magnetism
 Electricity flowing in a conductor involves:
– Electrical current (amperage)
– Potential (voltage)
– Resistance (ohms)
 The relationship between these elements is
stated in Ohm
Ohm’ss law
Amperage = Volts  Ohms
I=ER
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Electricity and Magnetism
 Two types of current flow are used in electrical
circuits
i it
– Direct current (dc)
• Electrons flow in one direction only
– Alternating current (ac)
• Electrons flow first in one direction, stop, and then
reverse their direction of flow
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Electricity and Magnetism
 Electrical circuits are made up of four basic
elements
–
–
–
–
Conductors
Control devices
Loading devices
El t i l energy source
Electrical
 Electrical circuits may be connected using
either a series or parallel format
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Electricity and Magnetism
 Series circuit places all of the loads on a single
currentt flow
fl path
th
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Electricity and Magnetism
 Parallel circuit provides an individual current
fl path
flow
th for
f eachh off the
th loads
l d
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General Characteristics
of Fluids
 Liquids and gases are both considered fluids
– Each substance is able to flow
– Each adjusts its shape to fit the container in which it
is held
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General Characteristics
of Fluids
 Major difference between liquids and gases is
compressibility
ibilit
– Liquids act much like a solid
– Gases change volume when pressurized
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Basic Properties of
Materials
 Specific weight is the weight of a specified
volume
l
off a substance
bt
att a given
i
temperature
t
t
and pressure
 Specific gravity is a comparison of the weight
of a substance to the weight of an equal volume
of water
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Pressure Measurements
in Fluids
 Several pressure scales are used to indicate the
pressure off a fl
fluid
id
–
–
–
–
–
Gauge pressure
Absolute pressure
Vacuum
Head
Atmosphere
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Pressure Measurements
in Fluids
 Under normal atmospheric pressure:
– Gauge pressure scale reads 0 psi
– Absolute scale reads 14.7 psi
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Fluid Reactions to Pressure
and Temperature
 Pascal’s law is a key principle
related to the operation of a
fluid power system
– States that pressure applied to a
confined nonflowing fluid is
transmitted undiminished to all
points in the fluid
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Fluid Reactions to Pressure
and Temperature
 Bernoulli’s theorem
states the total energy in
a volume of flowing
fluid is the same at every
point in its path of flow
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Fluid Reactions to Pressure
and Temperature
 Ideal gas laws are used in many situations in
pneumatic
ti systems
t
– Approximate how real gases react to pressure,
temperature, and volume changes
– Boyle’s law for constant temperature
– Charles’ law for constant p
pressure
– Gay-Lussac’s law for constant volume
– General gas law combines all three
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Review Question
Examine the descriptions below and then
id tif the
identify
th basic
b i machine:
hi
A. Two inclined planes fastened together.
B. A spiral inclined plane.
C. A circular form of a lever.
A. Wedge. B. Screw C. Wheel and axle
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Review Question
Energy in motion is known as _____ energy.
kinetic
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Review Question
The distance traveled in a standard basic unit of
time,
i
suchh as 3 per second,
d iis known
k
as _____.
velocity
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Review Question
Name four ways in which heat is generated in a
fl id power system.
fluid
t
A) Resistance to fluid flow in pipes
and hoses, B) flow over relief valves,
C) flow
fl through
h
h flow
fl controll valves,
l
and D) internal leakage of pumps and
motor.
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Review Question
The two factors that control the amount of
electricity
l t i it produced
d d by
b electromagnetic
l t
ti
induction are _____ and _____.
A) The rate of movement of the conductor
or the
th magnetic
ti field
fi ld andd B) the
th number
b off
magnetic lines of force cut.
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Review Question
Name the four basic elements of a basic
electrical
l t i l circuit.
i it
A) Electrical conductors, B) control devices,
C) loading devices, and D) source of
electrical
l
i l energy.
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Review Question
The basic concept of _____ law is that pressure
applied
li d to
t a confined,
fi d nonflowing
fl i fluid
fl id is
i
transmitted equally to all points in the fluid.
Pascal’s
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Glossary
 Absolute pressure
– A pressure scale
l where
h the
th zero point
i t represents
t a
perfect vacuum.
 Alternating current
– Electrical current that reverses direction on a
regular cycle due to a change in voltage polarity.
The common international standards are 50 or 60
cycles per second (or hertz).
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Glossary
 Atmosphere
–1
1. The pressure created by a column of gas
extending between space and the surface of Earth
at sea level.
– 2. A pressure of 14.7 psia.
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Glossary
 Conduction
– A basic term relating to the transfer of heat or
electricity through a material.
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Glossary
 Electron
– One of the three basic parts of an atom. These
negatively-charged portions of the atom orbit the
nucleus containing neutrons and protons.
 Force
– An influence on a body
y that causes it to accelerate
(move).
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Glossary
 General gas law
– A generall equation
ti that
th t expresses the
th relationships
l ti hi
between pressure, volume, and temperature when
applied to a gas (P1V1T1 = P2V2T2).
 Head
– The height of a column of water or other liquid
necessary to develop a stated pressure.
pressure
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Glossary
 Horsepower
– A standard unit of power equal to 550 foot-pounds
of work per second or 33,000 foot-pounds per
minute.
 Latent heat
– The amount of heat absorbed or released by
ya
substance without changing temperature during a
change of state.
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Glossary
 Lever
– One of the simple machines. Consists of a rigid bar
pivoted about a fulcrum. Used to multiply a force or
movement.
 Magnetism
– The pphenomena produced
p
byy the magnetic
g
lines of
force surrounding natural or electromagnets.
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Glossary
 Mechanical advantage
– The ratio of the force produced by a machine to the
applied input force.
 Parallel circuit
– An electrical or fluid power circuit that
simultaneously
y provides
p
multiple
p paths
p
for the
current or fluid to follow as it moves through a
circuit.
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Glossary
 Pascal’s law
– A bbasic
i scientific
i tifi law
l that
th t states
t t pressure applied
li d to
t
a confined, nonflowing fluid is transmitted
undiminished to all points in the fluid.
 Pressure
– Force per unit area, which is usually expressed in
pounds per square inch (psi) or bar.
bar
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Glossary
 Sensible heat
– Heat that can be measured with a thermometer and
will result in a feeling of warming or cooling as
heat is applied or removed from a substance. Does
not change the state of a substance.
 Specific gravity
– The ratio of the weight of a given volume of a
material to the weight of an equal volume of water
at 4° Celsius.
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Glossary
 Thermodynamics
– A science dealing with the relationships between
the properties of matter affected by temperature and
the conversion of energy from one form to another.
 Torque
– The turning
g or twisting
g force applied
pp
to a shaft.
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Glossary
 Vacuum
– A space in which the pressure is below normal
atmospheric pressure. The concept applies to a
variety of fluid power component and circuit
applications, such as the intake lines of both
hydraulic pumps and pneumatic compressors.
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Glossary
 Wheel and axle
– One of the simple machines, consisting of a wheel
attached to an axle. The common center of the
wheel and axle is the fulcrum, allowing the device
to act as a second or third class lever depending
where the effort is applied.
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