Hydraulics: Controlling the Transmission of Force and Energy

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Hydraulics Controlling the Transmission of
Force and Energy

• Symbolic Representation of Components Bowling
  Green Presentation
• July 21, 2009
• Dave Baker and Paul Turner

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Prior knowledge assumed to understand this
lecture.

• Can you guess how many beans are in the Jar?

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Carriage Brake System
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Brake System Components
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Typical Automotive Breaking System
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Master cylinder with 2 slaves
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Hydraulic Multiplication
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Putting the Stop to a Vehicle
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Typical Disk Brake

• Calipers travel a distance of 1/8 to 3/32 of an
  inch per wheel.

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Fluid Under Pressure
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Liquid Characteristics

• Liquid is a substance made up of molecules.
• Liquid molecules are continuously moving
  (molecular energy)
• Liquids take on the shape of their container.
• Liquids are relatively incompressible.

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Force Transmission Solid vs. Liquid

• Fluid power systems are capable transmitting a
  static force (potential energy)
• A force transmitted through a solid is
  transmitted in one direction only.
• A force applied to a confined liquid is
  transmitted equally in all directions throughout
  the fluid in the form of fluid pressure.

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Fluid Facts

• An ideal liquid will not compress at all.
• Common Hydraulic Oil is compressed approximately
  1 to 1.5 at a pressure of 3000 psi.
• Blaise Pascal (1623-1662) was a French
  mathematician and philosopher who discovered the
  phenomenon of fluid pressure transmission in
  1653.
• Pressure is equal to the Force divided by Area
• P F/A

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Pascals Law
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Hydraulic Pressure to Mechanical Force

• Hydraulic Pressure must be converted to a
  mechanical force before work can be performed.

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Mechanical Force Multiplication

• Mechanical forces can be multiplied using
  hydraulics
• The determining factor for force multiplication
  is the square inch area on which hydraulic
  pressure is applied

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Hydraulic Horsepower

• Hydraulic Horsepower GPM or gallons per minute
  X psi or pounds per square inch X .000583
• Hyd. Horsepower GPM x PSI x .000583
• 1 Horsepower is 746 watts

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Power is the rate of energy change per length of
time.

• It tells us the quantity of energy that changed
  during a certain period of time.
• The units of power are chunks of energy per
  amount of time.

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Why do we need a system?

• The reason for using hydraulics or any other type
  of energy transmission is to perform work.
• Accomplishment of work requires the application
  of energy to a resisting object.

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Positive Displacement Pumps

• A positive displacement pump you get constant
  flow regardless of pressure.
• You must have a method to drive the pump (this is
  known as a prime mover)

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Resistance of a Positive Displacement Pump

• Resistance to flow comes from the load and liquid
• There is a direct relationship between pressure
  and resistance
• Pump applies pressure the load determines how
  much

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Heat Generation in a Hydraulic System

• Extra energy which a pump applies to overcome a
  liquids resistance changes to heat.
• This is inefficiency
• Heat generation is caused by viscosity, fluid
  friction , and changing direction.

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Viscosity

• Viscosity is a measure of the resistance of a
  liquidss molecules to flow or slide past each
  other.
• Viscosity is affected by temperature.
• Saybold Universal Seconds (SUS) is a measure of a
  liquids viscosity
• In many industrial applications, the viscosity of
  oil is 150 SUS at 100 degrees F.

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Friction and Changing Directions
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Fluid Velocity

• Recommend Fluid Velocity in a pump suction line
  is 4 FPS or 4 feet per second.
• Recommended Fluid Velocity in a system return
  line is 8 FPS.
• Faster is not always better (cavitation can occur)

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Pressure Differential

• Pressure differential is the difference in
  pressure between any two points in a system.
• Indicates that working energy is present in the
  form of a moving, pressurized liquid.
• Measures the amount of working energy that
  changes to heat energy between two points.

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Hydraulic System Design

• Hydraulic systems are designed to avoid the
  generation of heat.
• Design should consider oil of the proper
  viscosity, piping of a proper size, and keep
  bends to a minimum.

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Physical World of a Machine

• Man invented machinery to work for him.
• All things on earth are surrounded by physical
  elements which hinder the performance of work

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Force

• It can cause a body to move.
• It can retard or stop a body which is moving
• One unit for measuring force is the pound.
• A Force is any influence capable of producing
  change in the motion of a body.

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What is Force

• The Pound is a unit of force in the English
  system.
• The Newton is its comparable metric unit.
• One Newton is equal to 0.2248 pounds

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Resistance

• Frictional resistance is always present between
  contacting surfaces
• Inertia is the reluctance of a body to a change
  in its motion.

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Inertia (the car or the load doesnt want to
start stop)

• Inertia as a resistance, is of concern in a fluid
  power system when a load has to be accelerated.
• Inertia as energy is a concern in fluid power
  systems when a load is required to be decelerated.

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Overcoming a Resistance

• In overcoming a resistance, energy changes form.
  For example, when friction is overcome, kinetic
  energy changes to heat energy. When gravity is
  overcome, kinetic energy changes to potential
  energy since it is raised to a higher level.

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Work, Power, Horsepower

• The unit of work in the Metric system is the
  Joule
• The unit of work in the English system is Ft. pd.
• All work is done within a certain time
• Power is the Speed that work is done.
• The unit for measuring power is Horsepower

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More about Horsepower

• The first measurement of horsepower was done by
  James Watt (1736-1819) a Scottish inventor.
• 1 hp 550 ft-lb/sec 33,000 ft-lb/min 42.44
  Btu/min 745.7 watts
• Metric Horsepower 542.5 ft.lb./sec.
• A human in good physical condition can output
  1/10 of a horsepower over sustained time
  increments.

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Effects of Pressure
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More about Pressure

• Pressure is force intensity or
  concentration.
• Fluid pressure is also potential energy.
• In the measure of pressure is the BAR. One BAR
  equals 14.5 psi.
• Pressure Force / Area

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Fluid Power Systems

• Hydraulic systems operate by means of a liquid
  under pressure. Generally, these are closed
  systems, meaning the liquid is returned to a
  reservoir.
• Pneumatic system operates by means of a gas under
  pressure. These are open systems the air
  returns to the atmosphere after use. We are
  standing in the reservoir.

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Why Symbols??

• Trouble shooting any system with pneumatics or
  hydraulics will be much easier if the Technician
  can understand the flow of power.
• Reading symbols correctly on a schematic will
  enable the Technician to find a fault and return
  the system to productivity.

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Fluid System Parts

• Hydraulic

• Pneumatic

• Reservoir (tank)
• Lines
• Pump
• Filters
• Valves
• Actuators (hyd. motors and cylinders)

• Receiver (tank)
• Lines
• Compressor
• Filters
• Valves
• Actuators (air motors and cylinders)

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Drawing Types

• Assembly drawing
• Pictorial-shows components in an outline that
  closely resembles the actual shape.
• Schematic-uses symbols to represent the
  components in a system. Shows the order of
  components but does not indicate size of the
  system.

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Schematics

• Hydraulic schematics are often included in
  employment tests.
• You should be familiar with the most common
  symbols.
• These will be included on a quiz.

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Common Symbols

• Hydraulic Pumps- see arrow direction
• Hydraulic Motors

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Arrows
Solid arrows, usually black, indicate hydraulic
components. Arrows that are outlined only
indicate pneumatic components.
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Common Symbols

• Electric Motor- M
• Cylinders-
  Double Acting
• Single Acting
• 
  Double Rod

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Common Symbols

• Squares indicate a type of valve.
• Squares are called envelopes
• The number of squares indicate valve positions

3 position valve 2 position valve
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Valve Control Methods(Manual)
Look in your text to identify these actuation
methods.
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Fluid Conditioners

• Diamonds indicate fluid conditioners
• Filters
• Heat exchangers (coolers)
• Air cooled
• Water cooled
• Heaters

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Common Symbols

• Pressure Relief Valve

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Check Valve
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A simple system
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A simple system, continued
Can you trace the flow path? Name as many
components as you can.
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More Symbols

• We will go over more symbols as class progresses.
• Next class session will include combining symbols
  to build systems, utilizing symbols to aid in
  troubleshooting.

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Thats All!