conditions that lead to additional trouble, since dirt mayenter an open system.Leaks are a frequent cause of trouble in hydraulicequipment. Generally, leaks are a result of excessivelyworn parts, abnormal and continuous vibration,excessively high operating pressures, or faulty orcareless assembly. External leaks usually have littleeffect on the operation of equipment other than a steadydraining of the oil supply. Even a small leak wastes oil,and the resulting unsightly appearance of a machine isindicative of poor maintenance procedures.External leaks may result from improperlytightened threaded fittings; crossed threads in fittings;improperly fitted or damaged gaskets; distorted orscored sealing rings, oil seals, or packing rings; scoredsurfaces of working parts; improperly flared tube ends;or flanged joints not seating squarely.Internal leaks usually result in unsatisfactoryoperation of the equipment. Large internal leaks aresignified by a loss of pressure and the failure ofequipment. While large internal leaks can usually belocated by installing pressure gauges in various parts ofthe equipment, the location of small leaks generallyrequires disassembly and visual inspection of the parts.Internal leaks may result from worn or scored valves,pistons, valve plates or bushings, or improperly fitted ordamaged gaskets.The most common symptom of trouble in ahydraulic system is an unusual noise. Some noises arecharacteristics of normal operation and can bedisregarded, while others are evidence of serioustrouble. Even though the exact sound indicating aspecific trouble can be learned only through practicalexperience, the following descriptive terms will give ageneral idea of which noises are trouble warnings.If popping and sputtering noises occur, air isentering the pump intake line. Air entering the system atthis point may be the result of too small an intake pipe,an air leak in the suction line, a low oil level in the supplytank, cold or heavy oil, or possibly the use of improperoil.If air becomes trapped in a hydraulic system,hammering will occur in the equipment or transmissionlines. When this occurs, check for improper venting.Sometimes, a pounding or rattling noise occurs as theresult of a partial vacuum produced in the active fluidduring high-speed operation or when a heavy load isapplied. This noise may be unavoidable under theconditions stated and can be ignored if it stops whenspeed or load is reduced. If the noise persists at lowspeeds or light loads, the system needs to be vented ofair. Air in a hydraulic system can also cause unevenmotion of the hydraulic motors.When a grinding noise occurs, it can usually betraced to dry bearings, foreign matter in the oil, worn orscored parts, or overtightness of some adjustments.The term hydraulic chatter is sometimes used toidentify noises caused by a vibrating spring-actuatedvalve, by long pipes improperly secured, by air in lines,or by binding of some part of the equipment.Squeals or squeaks indicate that the packing is tootight around some moving part or that a high-frequencyvibration is occurring in a relief valve.Electrical TroublesEven though troubles occurring in electricalequipment are the responsibility of the Electrician’sMate, the Engineman can help maintain the equipmentby making a few simple checks when electrical troublesoccur. Failure to have a switch in the ON position willcause unnecessary delay in operating electricalequipment. If the switch is closed and the equipment stillfails to operate, check for blown fuses or tripped circuitbreakers. Troubles of this type are usually the result ofan overload on the equipment. If a circuit breakercontinues to cut out, the trouble may be caused bydamaged equipment, excessive binding in the hydraulictransmission lines, or faulty operation of the circuitbreaker. Check for visual indication of open or shortedleads, faulty switches, or loose connections. Do notmake repairs to the electrical equipment or system. Donot open enclosures of electrical equipment, but doreport evidence of possible electrical failure to theElectrician’s Mate.Mechanical TroublesWhen electrohydraulically driven auxiliarymachinery becomesinoperative because of amechanical failure, a check should be made. Look forimproper adjustment or misalignment of parts; shearingof pins or keys; or breakage of gearing, shafting, orlinkage. Elimination of these causes should be doneaccording to the manufacturer’s instructions for thespecific piece of equipment.MAINTENANCEThe principal requirements necessary to keep ahydraulic transmission in satisfactory operatingcondition are regular operation, proper lubrication, and8-7
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