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MAGM 262

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MAGM 262

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    2. 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.

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

    4. 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.

    5. 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.

    6. Types of Hoses Common hose types Fabric braided Single wire braid Double wire braid Spiral braid

    7. 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.

    8. 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

    9. 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

    10. 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.

    11. 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

    12. 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

    13. 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.

    14. Hose Installation Twisted Hoses Can restrict oil flow Usually from tightening couplers incorrectly

    15. 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.

    16. 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.

    17. 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.

    18. 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.

    19. 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

    20. 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.

    21. 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.

    22. 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.

    23. Quick Disconnect Couplers Ball Bearing Coupler Utilize a spring loaded ball bearing for a metal to metal sealing valve.

    24. 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.

    25. 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.

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