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Hydraulic Hose Basics
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-Selecting Hose -Hose Types -Hose Assemblies-Hose Installation
      Hydraulic Hose is one of the most important parts of a hydraulic system. Hose gives flexability to a hydraulic system design connecting components over long distances,through tight spaces, or around corners.
SAE Standards       A Hose Standard, J517, sets the guidlines for the current SAE 100R series of hoses. Today there are 16 different hose styles which have to meet certain characteristics established by SAE. SAE doesn't certify manufacturers hose they only have given a guideline for manufacturers to follow.
Type of fluid Pressure Range
SAE # Petroleam oil Synthetic oil High-water content Temperature PSI ID inch
100R1 X X - 40 to 100oC 3000 3/16
100R2 X X - 40 to 100oC 5000 3/16
100R3 X X - 40 to 100oC 1500 3/16
100R4 X X - 40 to 100oC 300 3/4
100R5 X X - 40 to 100oC 3000 3/16
100R6 X X - 40 to 100oC 500 3/16
100R7 X X X - 40 to 93oC 3000 3/16
100R8 X X X - 40 to 93oC 5000 3/16
100R9 X X - 40 to 100oC 4500 3/8
100R10 X X - 40 to 100oC 10000 3/16
100R11 X X - 40 to 100oC 12500 3/16
100R12 X X - 40 to 121oC 4000 3/8
100R13 X X - 40 to 121oC 5000 4/4
100R14 X X X - 54 to 204oC 1500 1/8
100R15 X - 40 to 121oC 6000 3/8
100R16 X X - 40 to 100oC 5000 1/4
Hose Construction      Hydraulic hose contains three parts listed below.
  1. Inner Tube - (Has to be compatible with system fluid and flexible. Made of either synthetic rubber, teflon, or thermoplastics.)
  2. Reinforcement layer - (Consists of braided wire, textile yarn, or spiral-wound wire.)
  3. Protective Outer Layer - (Design to resist weather, oil, or abrasions.)
      How to prolong hose life. Here are a few things to stay away from. SAE has identified the following as things not to do:

  • twisting, pulling, kinking, crushing, or abrading hose.
  • bending past minimum bend radius
  • operating system above or below maximum or minimum tempurature
  • exposing hose to pressure surges or exposing hose to pressures past maximum operating pressure
  • intermixing hose, fittings, or assemblies.(Without seeing if they are compatible.)
How to Select a Hose      Here is a guideline to follow when selecting hose and couplings for your system. There are things to consider under each catagory below:
  1. Size - When selecting a replacement hose be sure to measure the inside and outside hose diameters with a precision caliper. You have to take the outer diameter of the hose into account when you have support clamps or the hose goes bulkheads. When you need to replace a hose assembly, cut the new hose to the same length as the replaced hose. Using hose that is too long in an application with moving parts may pinch or severe the hose. Using hose that is too short may cause hose the strech or contract. Consider possible hose shortening during operation;make the hose lengths slightly longer then the actual distance between connections.
  2. Temperature - All hoses are rated to a max fluid temperature of 200o to 300oF. Exposing your hoses to repeated high tempuratures will cause them to lose their flexibility; this problem will be accelerated using the improper viscosity fluid. Follow manufacturer's recomendations. You can lose up to 80% hose life ignoring temperature recomendations. If hose will be next to a heat source take into account the external temperatures. If hose is exposed to hot equipment parts use insulating sleeves and a additional barrier to protect it.
  3. Application - Make sure your hose will meet its minimum bending radius(in inches usually). If this radius requirement is exceeded you will score the hose. Run hose lines parrallel to machine contours when possible. This will reduce length of hose, flow restrictions, and hard angles in line.
  4. Materials - Always make sure that the fluid in your system is compatable with the hose or tubing you are using. Biodegradeable and green fluids sometimes are not chemically sound in some hoses and can cause problems. Most hoses are compatable with petroleum based fluids. 
  5. Pressure capablities - Working pressure of hose and tubing as to be greater or equal to your maximum working pressure(Including pressure spikes). Pressure spikes past the max pressure of the hose will shorten the life of the hose.
  6. Hose ends - Couplings have to be compatable to the hose they are attached to. Make sure to consider proper mating of thread ends to ensure leak-free sealing. There are two types of connections permanent and field-attachable. Permanently attached couplings are formed on the hose with machinery. These connections are economical and less complicated to install. The feild-type couplings are either clamped or screw-on. To ensure correct sizing you can use a caliper to measure the Outer diameter of male couplings or the inner diameter of female couplings. Also, thread pitch gages are used to find the numbers of threads per inch a fitting has.

    To identify a fitting:

    • type of seat — inverted (BSPP & DIN), regular (JIS & Komatsu) or flat (flange, flat-face)
    • seat angle — 30o (JIS, BSP, DIN and Komatsu) or 12o (DIN), and
    • type of threads — metric (DIN or Komatsu), BSP (BSPP, BSPT or JIS), or tapered (BSPT or JIS Tapered)

         SAE standards relating to hydraulic/ pneumatic fittings and assemblies specifically designed to eliminate leakage include:
    • J514 — straight thread ports/fittings
    • J518c — 4-bolt flange ports/fittings, and
    • XJ1453 — the number provisionally assigned to O-ring face seal fittings.
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