Hydraulic hose and crimp fittings

Hydraulic hoses and press fittings are central components of modern hydraulic systems. Hoses transport hydraulic fluids under pressure, while press fittings ensure a secure and leak-proof connection between hose and hydraulic system. Together they enable precise control and power transmission – in mobile applications such as agricultural machinery and excavators as well as in stationary applications such as machine tools, presses or robotics.

Hydraulic hoses have a multi-layer construction:

• Inner tube: Chemically resistant, usually made of nitrile, polyamide or polyester.
• Reinforcement: Textile or steel wire braids, possibly glass or carbon fibers – determines pressure resistance and flexibility.
• Outer cover: Abrasion, oil and weather resistant, usually made of polyamide or polyurethane.

Press fittings are usually made of steel or stainless steel and are permanently pressed onto the hose with special tools. Reuse after pressing is excluded.

• Single-layer reinforcement: One textile or steel wire layer. Flexible, lightweight, for low-pressure systems.
• Multi-layer reinforcement: Multiple layers of textile or wire. Higher pressure resistance, less flexible. Ideal for medium pressure.
• Spiral reinforcement: Multiple spiral wire layers. Very high pressure resistance, robust, but stiffer. For high pressure, construction machinery and dynamic loads.

• High flexibility: Easier installation, especially with moving parts.
• Vibration and shock dampening: Protection against material fatigue.
• Easy assembly: Quick and uncomplicated.
• Standardization: Uniform sizes facilitate replacement and maintenance.

Important selection criteria:

• Pressure range: Must withstand system pressure including reserve.
• Medium: Hose material must be compatible with hydraulic fluid.
• Temperature range: Consider environment and medium.
• Environmental conditions: Abrasion, UV, moisture, chemicals.
• Bend radius & flexibility: Must fit the installation.
• Standards & regulations: Compliance with DIN/ISO standards.

• Nitrile rubber (NBR/HNBR): Standard for mineral oil-based oils. HNBR also for synthetic oils and higher temperatures. Not suitable for water-based media.
• EPDM: For water-based and glycol-containing media. Unsuitable for oil and fuel.
• PTFE (Teflon): Very chemically resistant, wide temperature range. Ideal for aggressive media such as phosphate esters.
• Viton (FKM): For fire-resistant, synthetic or aggressive hydraulic fluids and high temperatures.

When in doubt, the safety data sheet of the hydraulic fluid should be checked.

Assembly is carried out with special crimping machines according to manufacturer specifications:

• Fitting must align exactly at the hose end.
• After crimping, the diameter of the crimp sleeve must be checked.
• Improper crimping poses safety risks.
• Reuse of crimped fittings or hoses is inadmissible.

• Inspection after assembly: Immediate function check before initial operation.
• Regular inspection: At least annually by qualified person. Shorter intervals under harsh operating conditions.
• Extraordinary inspection: After accidents, collisions, overheating or long standstills.
• Replacement interval: Maximum 6 years (including 2 years storage). Under extreme conditions often shorter, e.g. 2 years.

Extension beyond 6 years is only permissible with risk assessment and shortened inspection intervals.