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Hydraulic Hose Assemblies - Thorburn Flex Inc

Hydraulic Hose Assemblies - Thorburn Flex Inc

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Technical Data<strong>Hose</strong> failures normally aren’t a problem– the hose is replaced and the equipment goes back in operation. However, whenthe same problems keep occuring with the same equipment, one must determine their causes and correct them.Improper ApplicationBegin with the most obvious and commoncause of hose failures, improper application,and compare the hose specifications withthe requirements of the application. Payattention especially to the following:1. Maximum operating pressure of thehose.2. Recommended temperature range ofthe hose.3. Whether the hose is rated forvacuum service.4. Fluid compatibility of the hose.Check these against the requirements of theapplication. If they don’t match up, anotherhose must be selected. A <strong>Thorburn</strong> representativecan help you select the proper hose.Analyzing FailuresA physical examination of the failed hose can often offer a clue to the cause of failure. Following are 20 symptomsto look for, along with the conditions causing them:1. Symptom: The hose tube is very hardand has cracked.Analyzing FailuresImproper Assembly and InstallationThe second major cause of premature hosefailures is improper assembly and installationprocedures. This can involve any factorfrom using the wrong hose fitting to poorrouting of the hose.Your <strong>Thorburn</strong> representativecan help you solve this problem.External DamageExternal damage ranges from abrasion andcorrosion to a hose crushed by a forklift truck.Once the cause is identified, most of theseproblems are easily solved. The hose can bere-routed or clamped or a fire sleeve or abrasionguard can be used. With corrosion, thesolution may simply be to switch to a hose witha more corrosion resistant cover or re-routingthe hose away from the corrosive element.3. Symptom: The hose has burst.Examination of the wire reinforcementafter stripping back the cover reveals randombroken wires the entirelength of the hose.Faulty EquipmentA malfunction in equipment is a factor to beconsidered since prompt corrective actioncan avoid serious and costly equipmentbreakdown.Faulty <strong>Hose</strong>Sometimes a failure is caused by the hoseitself. The likeliest cause of a faulty rubberhose is old age. Check the lay line on the hoseto determine the date of manufacture. Thehose may have exceeded its recommendedshelf life. If, after exhausting other possibilities,you suspect the problem is in the manufactureof the hose, contact <strong>Thorburn</strong>. Given effectivequality control methods, the odds of a faultyhose being released for sale are tiny.deteriorated badly.Cause: Heat has a tendency to leach theplasticizers out of the tube. This is amaterial that gives the hose its flexibilityor plasticity. Aerated oil causes oxidationto occur in the tube. This reaction of oxygenand heat will greatly accelerate thehardening of the hose tube. Cavitationoccuring inside the tube would have thesame effect.2. Symptom: The hose is cracked bothexternally and internally but the elastomericmaterials are soft and flexible atroom temperature.Cause: Probably the hose was flexedunder intense cold ambient conditions.Most standard hoses are rated to -40°F(-40°C). Some <strong>Thorburn</strong> hoses are ratedat -55°F (-49°C). Military specified hosesare commonly rated to -65°F (-54°C).Teflon hose is rated to -100°F (-73°C).Some Polyon thermoplastic hoses arerated -65°F (-54°C).Cause: This points to a high frequencypressure impulse condition. SAE impulsetest requirements for a double wire braidreinforcement are 200,000 cycles at 133%of the recommended working pressure.The SAE impulse test requirements for afour spiral wrapped braid reinforcement(100R9) are 300,000 cycles at 133% ofthe recommended working pressure andat 200°F (93°C). If the extrapolated impulsesin a system amount to over a million ina relatively short time a spiral reinforcedhose would be the better choice.4. Symptom: The hose has burst, but thereis no indication of multiple broken wiresthe entire length of the hose. The hosemay have burst in more than oneplace.Cause: The pressure has exceeded minimumstrength of the hose. Either astronger hose is needed or the hydrauliccircuit has a malfunction which is causingunusually high pressure conditions.5. Symptom: The hose has burst. An examinationreveals that the wire braid is rustedand the cover has been cut, abraded or7Cause: The primary function of the cover isto protect the reinforcement. Elements thatmay destroy or remove the hose covers are:1. abrasion2. cutting3. battery acid4. steam cleaners5. chemical cleaning solutions6. muriatic acid (for cement clean-up)7. salt water8. heat9. extreme coldOnce the cover protection is gone, the wirereinforcement is susceptible to attack frommoisture or other corrosive matter.6. Symptom: The hose has burst on the outsidebend and seems elliptical in the bentsection. In the case of the pump supply line,the pump is noisy and very hot. Theexhaust line on the pump is hard and brittle.Cause: In both cases, the likeliest cause isa violation of the minimum bend radius.Check the minimum bend radius and makesure that it is within specifications. In thecase of pump supply line partial collapse ofthe hose is causing the pump to cavitatecreating both noise and heat. This is a mostserious situation and will result in catastrophicpump failure if not corrected.

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