MAGM 262

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MAGM 262
Hydraulic Lines and Fittings
Mr. Conrado
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Lines and Fittings

• A vital part of any hydraulic system
• Connect the components of any hydraulic system
• Conduct fluid from one component to the others
• Are often a cause of repair
• An understanding of their construction and design
  will help avoid costly repairs.

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Hoses

• Provide flexible connections between components.
• Permit some movement of components, absorb
  vibration and pressure surges.

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Hose Selection

• Always replace damaged hoses with the kind of
  hose specified in the technical manual or parts
  catalog.
• Hose construction follows the SAE standards and
  tolerances. Some of which are
• Inside diameter
• Outside diameter
• Maximum operating temperature
• Minimum burst pressure
• Minimum bend radius
• Temperature limits
• Hose size is determined by the amount of flow
  needed. Too little will cause flow restriction,
  slow operation, and generate heat. Too large may
  cause rupture due to the greater internal surface
  area of the hose.

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Hose Selection

• Hose pressure rating is based on operating
  pressure and burst pressure. The hose must
  withstand normal operation plus pressure surges.
  
• High temperature hoses can be specified if fluid
  temperature is exceptionally high.

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Types of Hoses

• Common hose types
• Fabric braided
• Single wire braid
• Double wire braid
• Spiral braid

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Types of Hoses

• Fabric Braided Hose
• Construction
• Inner tube Synthetic rubber
• Reinforcement One fiber braid or woven fiber
  reinforced with spiral wire to prevent collapse.
• Cover Synthetic rubber, oil and abrasion
  resistant.
• Uses
• Petroleum based oils, gasoline, or fuel oil.
• Suction lines
• Low pressure return lines
• Temperature ranges
• -40 to 250F
• Vacuum
• 30 in Hg.
• Fabric braided hoses should not be used for
  hydraulic pressure lines.

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Types of Hoses

• Single wire braid hose
• Construction
• Inner Tube Synthetic Rubber
• Reinforcement
• Two Fiber braids or one braid of high tensile
  steel wire
• Cover
• Synthetic Rubber oil and abrasion resistant
• Uses
• Hydraulic lines, fuel oil, or gasoline
• Temperature ranges
• -40 to 250F

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Types of Hoses

• Double Wire Braid hose
• Construction
• Inner Tube Synthetic Rubber Oil resistant.
• Reinforcement
• Two braids or more of high tensile steel wire
• Cover
• Synthetic Rubber oil and abrasion resistant
• Uses
• High pressure Hydraulic lines, fuel oil, or
  gasoline
• Temperature ranges
• -40 to 200F

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Types of Hoses

• Spiral Wire hose
• Construction
• Inner Tube Synthetic Rubber Oil resistant.
• Reinforcement
• Multiple spiral high tensile steel wire and one
  fabric braid
• Cover
• Synthetic Rubber oil and abrasion resistant
• Uses
• Very high pressure Hydraulic lines, fuel oil, or
  gasoline
• Temperature ranges
• -40 to 200F
• Spiral wire is recommended in high flexing
  applications. The spiral wire strands do not rub
  and wear as much as the braided strands do.

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Hose Failures

• When hydraulic hoses fail dangerous conditions
  can occur. Such as penetration of skin,
  mechanical damage.
• Troubleshooting Hoses
• Mainly done by inspection and replacement.
• Cracks and splits
• Pinhole leaks
• Incorrect hose length
• Improper installation
• Incorrect type of hose
• Incorrect fittings

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Hose Failures

• Cracks and Splits
• Outer-cover cracks and splits do not always mean
  a hose failure. However if it leaks the source
  must be found and fixed immediate
• Do not look for Cracks, splits or leaks with your
  hands or fingers.
• Leaks
• Reduce efficiency and lead to heat and wear
  problems

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Hose Failures

• Hose length
• Hoses must be of correct length. If too short,
  stretching will cause failure. If too long the
  hose will vibrate and flex until it failures.
• Hydraulic hoses should never be looped.

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Hose Installation

• Twisted Hoses
• Can restrict oil flow
• Usually from tightening couplers incorrectly

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Hose Installation

• Hose Routing
• Often the cause of premature hose failure.
• Incorrect routing may cause abrasion, kinking,
  twisting, and burning
• Keep hoses away from heat. If necessary use heat
  shields
• When removing complicated hoses lay a wire in the
  hose path before removal. The wire will aid you
  during installation.
• Do not move clamps or brackets to new locations
  when replacing hoses.

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Tubing

• Tubing is used where flexibility is not needed.
  Correctly sized, shaped and installed tubing will
  add to reliability.
• Selection
• Size Must have correct inside and outside
  diameters, maximum operating pressure, minimum
  burst pressure, and temperature capacity.
• Types of tubing include
• Copper - Low pressure, moderate temps, and low
  vibration applications.
• Aluminum Easily bent and flared but must be
  used in only low pressure applications.
• Plastic Nylon is suitable for low pressure,
  moderate temp systems but will melt at high temps
  and break in cold temps.
• Steel The strongest of tubing. Can take high
  pressures and temperature extremes. More
  difficult to form and manipulate.

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Couplers and Fittings

• Couplers join hoses to components, change hose
  size, connect lines, and route houses through
  bulk heads
• Hose Couplers
• Fittings attached to the end of hoses
• Aluminum
• Steel
• Brass
• Copper
• Stainless
• plastic
• Must provide a strong, long lasting seal.
• High pressure and medium pressure fittings look
  the same. To reduce confusion manufactures mark
  high pressure fittings with notches.

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Couplers and Fittings

• Permanent Hose Fittings
• Are discarded with the hose
• Are either crimped or swedged onto the hose.
• Reusable hose fittings
• When the hose wears out the fittings can be
  reused.
• Thread types can often be interchanged.
• Skive fittings Require the hose cover to be
  removed from the end before installation
• Non-Skive The hose cover remains intact during
  and after installation.

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Sealing Methods of Fittings

• The Six standard sealing methods for hydraulic
  couplers and fittings.
• Pipe Thread
• Dry seal for cone seat
• O-Ring seal
• Split flange o-ring seal
• O-ring face seal

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Quick Disconnect Couplers

• Used when lines must be connected and
  disconnected often
• They are self sealing devices that do the work of
  two shut off valves and a coupler
• Are fast and easy and keep fluid loss to a
  minimum.
• No need to bleed the system each time a hook-up
  is made
• However dust plugs must be inserted into coupler
  port to prevent fluid contamination.

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Quick Disconnect Couplers

• Poppet coupler
• Have a self sealing poppet in each half. When
  closed poppet seal the oil. When connected the
  poppet push each other off their seats. The
  couplers are locked in place by a ring of balls.

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Quick Disconnect Couplers

• Sleeve and Poppet Coupler
• One half has a self sealing poppet the other has
  a tubular valve and sleeve. The sleeve is
  inserted firs and gives an added margin of
  sealing against oil loss or air entry.

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Quick Disconnect Couplers

• Ball Bearing Coupler
• Utilize a spring loaded ball bearing for a metal
  to metal sealing valve.

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Quick Disconnect Couplers

• Straight Through Coupler
• Allows for full flow of hydraulic oil. Used when
  full flow is required and separate shut off is
  installed.

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Quick Disconnect Couplers

• Rotating Ball
• Utilize a quarter turn ball valve in each half.
  Ball valve must be opened and closed during
  transition. Used for low pressure high flow
  systems.