COVER ASSEM. 7M6588 - Caterpillar

Hydraulic Hoses
Illustration 1 g01061345
Hydraulic hoses are made of several layers of material. The various layers are shown in illustration 1:
Polymer inner tube - Seals the oil from leakage.
Reinforcement layer - Either fiber for low pressure or wire for high pressure in order to support the inner tube, one to six layers may be used.
Polymer friction layer - separate reinforcement layers to prevent rubbing and subsequent wear.
Outer cover - Protects the hose from wear and other components.Pressure Ratings of Hoses
Illustration 2 g01061347
Depending on the system requirements, mobile equipment may use a variety of low, medium, and high pressure hoses. The various hoses are shown in illustration 2:
XT-HOSE-3 (Four spiral) - High pressure: 17500-28000 kPa (2500 - 4000 psi)
XT-HOSE-5 (Four/six spiral) - High pressure:41400 kPa (6000 psi)
XT-HOSE-6 (Six spiral) - High pressure: 41400 kPa (6000 psi)
716 (One-wire braid) - Medium/low pressure:4300 - 19000 kPa (625 - 2750 psi)
844 (Hydraulic suction) - Low pressure: 690 - 2070 kPa (100 - 300 psi)
556 (One wire braid fabric) - Medium/low pressure: 1725 - 10350 kPa (500 - 3000 psi)
1130 (Engine/air brake) - Medium/low pressure: 1725 - 10350 kPa (1250 - 3000 psi)
1028 (Thermoplastic) - Medium pressure: 8620 - 207000 kPa (2250 - 5000 psi)
294 (two wire braid) - Medium/high pressure:15500 - 34500 kPa (2250 - 5000 psi) The smaller the inside diameter of a hose, the higher the pressure rating within that type of hose. The inside diameter of a hydraulic hose ranges from 0.188 inch (3/16 inch) to 2.000 inch (2 inch) .Types of Hose Coupling
Illustration 3 g01061348
Hose couplings are used at both ends of each length of hose in order to connect the hose to the hydraulic system components. Three different methods that are used to attach the couplings directly to the ends of the hose are shown in illustration 3.
Crimp On (top) - Permanent, not reusable, with a low failure rate and works well in all pressure applications.
Screw Type (lower right) - Reusable, can be installed on hose in field with hand tools, usable in low and medium pressure applications.
Collet Type (lower left) - Reusable, designed for high pressure hose applications, must be assembled and disassembled using a hose press.The end of the hose coupling that is not directly attached to the hose will attach to another component of the hydraulic system. There are two general types of coupling ends that are used: flange type and threaded connector type. There are two different thickness of flange type ends for some given size hoses, determined by the maximum system pressure. There are many different threaded connector ends, determined by the fittings to which they are to connect. Threaded connectors are generally restricted to hose size 1.25 inch in diameter or smaller.