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MATERIALS HANDLING


potential fault – the hydraulic power pack should be shut off and depressurised. A hose consists of an inner metal braid, connected


to the ferrule at either end via a robust crimp, and protected by an external rubber sleeve. Should the braid be visible due to rubber wear, the hose should be replaced as this could be indicative of damage to the inside of the hose and leaves the braid open to rust and abrasion. This can be caused by excessive pressure exerted on the hose, for example, being driven over by forklifts or trapped under other machinery. Where the rubber casing remains intact but the inner braid is damaged, a tell-tale sign is blistering or swelling of the outer coating. Here, oil is seeping through the braid and travels between the two materials, meaning it is only a matter of time until the rubber housing gives way. Another cause of blistering could be an incompatibility between the hydraulic fl uid and the hose materials, again pointing to replacement. A hard, brittle rubber casing is indicative of its


maximum operating temperature being regularly exceeded, meaning it should be replaced with a more suitable product. Conversely, a tube exposed to temperatures below its optimum level will remain soft and fl exible but display hairline cracks, in which case either the system temperature should be raised or the hose replaced. Frays or loose wires at either end of a hose


point to excessive hose movement, which may be the result of vibration, pressure surges, or too short a hose. If vibration can be identifi ed as the cause then clamps or dampers may be required to support the hose if re-routing is not an option. An amount of slack should always be allowed as assemblies shrink when pressurised, so a longer hose may be required. Hoses should always be specifi ed with a higher maximum operating pressure than the system itself to account for surges, however spiral reinforced hoses are available specifi cally for severe pulsing applications if necessary.


SUPPORTING ROLE FOR HEAVY HOSES


Hoses often need to be supported by fi ttings to prevent them being bent out of shape or exerting pressure at weak points. Fraying can occur as a result, exposing parts that can corrode, wear or rust. As hoses of 6-8m in length and 1inch in diameter are not uncommon, they are typically very heavy and without


support, will put pressure on the crimp and


An example of a hose in poor condition


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fi tting at one end or both. Persistent pressure can distort and break a crimp, and oil drips can quickly become a jet under normal operating conditions. When installing supports for hydraulic hoses, it is recommended to replace the hoses at the same time to account for previous wear and tear when unsupported. Any twists or tight bends should be inspected for damage and, in the case of twists, care should be taken not to overtighten the fi tting as this itself can cause pressure. When replacing a hose, engineers should ensure it


is within its ‘best before’ date. Products should show the date of manufacture of all components along with the date of assembly, as hoses have a shelf life – the nitrile rubber casing loses its eff ectiveness after around fi ve years due to UV exposure, so care must be taken to ensure the hose is within date and professionally swaged to ensure components have not been changed or replaced. Brammer’s fl uid power solutions team has extensive experience in the inspection, design and repair of hydraulic hose assemblies. ■


Terry Davis is national technical manager at Brammer. www.brammeruk.com


A hydraulic system can contain as much as 2,000l of oil,


which can completely drain out of a damaged hose within 20 minutes


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