MNET 350 Fundamentals Primarily Hydraulics

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MNET 350 Fundamentals(Primarily Hydraulics)

• Primarily from Chapters 12

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Pascals Law(Blaise Pascal 1623-1662)

• Pressure applied to a confined liquid is
  transmitted undiminished in all directions, and
  acts with equal force on all equal areas, and at
  right angles to those areas.
• This is the basis for hydrostatics. The static
  part implies that the fluid is confined and at
  rest, or nearly so.
• If the fluid is moving we will have to consider
  pressure drops.

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Fluid Stiffness

• We will consider hydraulic fluid to be
  incompressible for many of our circuits
• Later we will find that it is not truly
  incompressible but acts like a stiff spring
• Bulk modulus quantifies the fluid stiffness and
  is determined as ß (-?p)/(?V/V)
• A typical value for petroleum oil is about
  250,000 psi

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Similarities to Electrical Circuits

• Pressure is the analog to Voltage
• Fluid flow rate is analogous to Current
• Line loss in a hydraulic circuit is analogous to
  the I2R loss in an electrical conductor
• Pressure drops across an orifice as voltage drops
  through a resistor
• Power in a hydraulic circuit is a function of
  Flow x Pressure, as in EE it is I x V

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Schematic Diagrams

• Similar to electrical schematics, but with
  different symbols
• You MUST learn to read schematic diagrams and
  construct them if you want to be competent in
  fluid power systems
• Your text has an appendix (B) with accepted ANSI
  and ISO schematic symbols. REVIEW IT! See if
  you can see how the symbol represents the function

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Hydraulic Schematic Symbols

• Fixed Displacement Pump
• Variable Displacement Pump
• Reservoir
• Filter or screen
• Pressure Relief Valve
• Directional Control Valve (3 pos, 4 way)
• Spring return and lever actuated

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A Few More Schematics

• Linear actuator, or cylinder (double acting)
• Hydraulic motor (fixed displacement)
• Motor variable displacment, reversible
• Working Line
• Pilot or control line

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Cylinder Clamp Form Circuit
Double Acting Cylinders
Pressure Reducing Valve
DCVs (3Pos-4Way, Spring Return, Solenoid Actuated)
Sequence Valve
Fixed Displ. Pump
Filter Strainer
Pressure Relief Valve
Reservoir