ENGINEMAN 1 & Cpins or keys; or breakage of gearing, shafting, orlinkage. Elimination of troubles resulting fromany of these causes should be accomplished ac-cording to the manufacturer’s instructions for thespecific piece of equipment.MAINTENANCEThe principal requirements necessary to keepa hydraulic transmission in satisfactory operatingcondition are regular operation, proper lubrica-tion, and the maintenance of all the units and thefluid in the required state of cleanliness. Regularoperation of hydraulic equipment prevents theaccumulation of sludge and the freezing of adja-cent parts, and aids in preventing corrosion. Thenecessity of proper lubrication and cleanlinesscannot be too strongly emphasized.Detailed instructions on the maintenance ofa specific unit should be obtained from theappropriate manufacturer’s technical manual, butthe following general information will also beuseful.The Fluid SystemIf an inspection of an oil sample drawn froma hydraulic system reveals evidence of water,sludge, or acidity, the system must beDRAINED, then CLEANED with the prescribedacid-free cleaning fluid (flushing oil), andFILLED with clean hydraulic oil. A hydraulicsystem may be drained and cleaned as follows:1. Remove permanent filters and wash themin flushing oil. Then use low pressure air for dry-ing purposes. If filters have replaceable elements,install new elements.2. Drain the system of old hydraulic oil ascompletely as possible.3. Close all connections and fill the systemwith acid-free cleaning fluid.4. Start and operate the unit under idling con-ditions in order to fill the system thoroughly withthe cleaning fluid.5. Secure the unit and allow it to stand idlefor the prescribed period (usually about an hour).This period of idleness permits the cleaning fluidto dissolve any sludge.6. Start and operate the unit with a light loadfor a short interval of time (3 to 5 minutes, unlessotherwise specified). Allow the equipment to standidle for about 15 minutes, then repeat the wholecleaning process. Do this two or three times.Never operate a hydraulic unit with a full loadwhen it is filled with cleaning fluid. Keep theoperating pressure as low as possible.After each short operating period, turn thecleaning handles of edge type filters (if installed)and drain from the filter an amount of cleaningfluid equal to its volume.7. If time permits, allow the system to standidle for an additional hour following the seriesof short operating periods.8. Drain the system of cleaning fluid. Recleanpermanent filters, if necessary; install newreplaceable filters. Close the system, and fill itwith the proper hydraulic oil.As the system is filled, the hydraulic oil shouldbe strained through a fine wire screen of 180 or200 mesh. If oil is not clean, it should be runthrough a centrifuge. Adequate protection shouldbe provided against dust and moisture. Moistureshould be expelled from the oil before it is pouredinto a system; oil with noticeable water contentshould be rejected or centrifuged.When a hydraulic system is being filled, suf-ficient hydraulic fluid should be used to com-pletely fill the active parts of the mechanism,leaving no air pockets. Air valves should beopened during the filling process, so that air canescape to the oil expansion box. Be sure the valvesare closed tightly after the system has been filled.Pumps and MotorsWhether the pumps and motors of hydraulictransmissions are of the axial or radial piston type,the maintenance procedures, as well as theoperating principles, are relatively the same. Ingeneral, maintenance information on other typesof pumps also applies to hydraulic pumps andmotors.Neoprene is utilized as a seal around the shaftsof most modern hydraulic pumps and motors, butother types of shaft packing are also used.7-18
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