Fluid Power

1
Fluid Power

• Control Power
• CVHS

2
Fluid Power

• Fluid power systems are used to transmit power
  from one point to another
• They are used in many transportation devices
• example brake system on a car
• 2 types of Fluid Power Systems
• 1) Hydraulic systems are those that use a liquid,
  such as oil as the transmitting medium
• 2) Pneumatic systems use air or gas as the medium

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Hydraulic Pneumatic

• Hydraulic fluids can not be compressed
• Pneumatic fluids are considered gases and are
  compressible
• Hydraulic fluids must have complete hydraulic
  circuits. Return lines must be used, and a
  reservoir is needed to hold the extra fluid
  (closed system)
• Pneumatic fluids do not need complete circuits.
  Air can be dumped into the atmosphere
  (open system)

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Force Pressure

• Force is defined as the pushing or pulling
  action of one object upon another
• force usually causes an object to move
• usually measured in pounds
• Pressure is defined as a force acting upon an
  area
• measured commonly in psi

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Types of Pressure

• Pressure per square inch-absolute (psia)
• Measure of pressure of a fluid starting at zero
  atmospheres and working upward to a maximum
  pressure
• An atmosphere is a unit of pressure in which 14.7
  psi of pressure is considered absolute at sea
  level
• Pressure per square inch-gage (psig)
• Measures the pressure of a fluid above or below
  the surrounding atmosphere

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Pascals Law

• A pressure applied to a confined fluid is
  transmitted undiminished to every portion of the
  surface of the containing vessel
• Also states Pressure on a fluid is equal to the
  force applied divided by the area
• P F / A
• where
• P pressure in psi
• F force applied in pounds
• A area to which the force is applied

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Applying Pascals Law

• Given
• Pressure 200 psi
• Force 100 lbs
• Determine the Area to which the Force is Applied
• P F / A
• A F / P
• A 200 lbs / 100 psi
• A 2 in2

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Boyles Law

• The volume of a gas varies inversely with the
  pressure applied to it, provided the temperature
  of the gas remains constant
• This means that as the volume of a gas is reduced
  such as in an engine when the piston compresses
  air - the pressure is increased
• If the volume was halved, the pressure would be
  doubled
• Note remember hydraulic fluids cannot be
  compressed, but pneumatic fluids can

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Charles Law

• As the temperature of a gas increases, the
  volume of the gas increases proportionally, if
  the pressure is kept constant
• This means that as the temperature of a gas goes
  up, so will the volume of that gas
• If the temperature is doubled, then the volume is
  also doubled (unconfined gas)

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Measuring Pressure

• Bourdon Gage
• Can read either pneumatic or hydraulic
  fluid
  pressure
• Tube bends out with pressure, hook end is
  connected to
  the end of the pressure needle
  (mounted on a pivot)
• Manometer
• Used to read pneumatic pressures and vacuum
  
  readings
• U shaped tube with a fluid inside (fluid varies
  dependent upon
  application - i.e. mercury
  used for high pressure)

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Fluid Characteristics

• Viscosity - the fluidity or thickness of the
  liquid at a specific temperature
• Measured by a device known as a Saybolt universal
  viscosimeter - (SUS) Saybolt universal seconds
  test
• Viscosity Index - a measure of how much the
  viscosity of a fluid changes with a given
  temperature
• Usually, the higher the VI, the smaller the
  relative change in viscosity with temperature
• Pour Point - the temperature at which the fluid
  ceases to flow

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SAE Ratings

• SAE - Society of Automotive Engineers
• ratings in viscosity
• they use the Saybolt universal seconds test (SUS)
• 10W-30
• rating with the W after it (10) means it was
  tested at 0oF
• if no W after (30), it was tested at 210oF
• thicker fluids have higher SAE ratings
• sometimes a third rating is mentioned, the
  middle, - tested at 150oF

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Fluid Power Pumps

• Provide the pressure needed for a fluid power
  system to operate
• Hydraulic types include
• Gear Pumps
• Centrifugal Pumps
• Reciprocating Pumps
• Pneumatic are called air compressors
• Use pistons to compress air (reciprocating)
• May be single or multi stage
• Usually send air to a receiver (tank)

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Fluid Power Conductors

• Provide a path for
  the pressurized fluid to travel
• Includes hoses (flexible)
  and lines (ridged)
• Must be properly sized
  to suit system requirements

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Control Devices

• Valves control fluid pressures, flow rates and
  directions
• Include
• Pressure Relief Valves
• Flow Control Valves
• Pressure Control Valves (regulator)
• Directional Control Valves

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Fluid Power Actuators

• These devices put the pressurized fluid to work
• Cylinders are devices that use pressure to move
  in or out (linear)
• Single Acting
• Double Acting
• Motors are devices that use pressure to rotate
  (spin)

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Fluid Power storage

• Pneumatic use a receiver (pressure tank) to
  store large volumes of pressurized air
• Hydraulic systems may use an accumulator to store
  a small amount
  of pressurized liquid
  (acts like a capacitor)

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Fluid Power Components Example Circuit-

• http//www.patchn.com/tutr-hyd.htm

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Assignment

• Chapter 9 Questions
• 1-10
• 23-34