Chapter 7—AUXILIARY MACHINERYOn some modern hydraulic transmissions, theSHAFT STUFFING BOX PACKING is of thesquare-braided pure asbestos type. This packingis easily removed, but care must be taken toensure that it is not replaced too tightly. If prop-erly installed, this packing makes a tight jointwhen you apply light pressure. If packing wearsout quickly, the shaft should be inspected forroughness. If a lathe is available, roughness maybe eliminated from a shaft by a finishing cut tosmooth the surface. If a lathe is not available, itmay be necessary to replace the shaft. Packingshould be renewed at prescribed intervals toeliminate the possibility of the packing becominghard and scoring the shaft. When packing is be-ing replaced, make certain that there is a uniformthickness around the shaft. An excess of packingon one side of the shaft will cause shaft deflec-tion and may cause breakage. Stuffing boxesshould be packed loosely and the packing glandset up lightly to allow adequate leakage for cool-ing and lubrication.There will be very little likelihood of pooralignment between the driving and drivenmembers of a hydraulic transmission if thewedges, shims, jacking screws, or adjustingsetscrews are properly set and secured when con-necting units are installed. However, when acasualty occurs or a unit is replaced, it is possi-ble for units to get out of alignment sufficientlyto cause severe stress and strain on the couplingand connected parts. Excessive misalignmentshould be eliminated as soon as possible by replac-ing any defective parts and by readjusting thealigning devices. If this is not done, pins,bushings, and bearings will wear out too fast andwill have to be replaced frequently.Since there is no end play to either the pumpshaft or the motor shaft, flexible couplings aregenerally used in hydraulic transmissions. Suchcouplings permit satisfactory operation with aslight misalignment, without requiring frequentrenewal of parts.Piping and FittingsIf properly installed, the piping and valves ofa hydraulic system are seldom a source oftrouble, except for leakage. Since some leaks,however, can be of sufficient seriousness to causea reduction in the efficiency of the unit, frequentinspections should be made for leakage and stepsshould be taken to eliminate any leakage found.If leaks occur at a flanged joint in the line ofa hydraulic system, tighten the flange boltsevenly, but not excessively. If the leaks persist,use the auxiliary gear while the leaking flange isbeing refitted with copper asbestos or "O" ringpacking. Be sure the flange surfaces are cleanedcarefully before the packing is applied.CAUTION: Exposure to asbestos fibers is arecognized health hazard. Refer to N.S.T.M.chapter 635 for safety requirements applicable tohandling asbestos packing and gaskets.Operation of hydraulic equipment may becontinued while leakage repairs are being madein some parts of the system if certain measuresare taken. When lines in an auxiliary system leak,they should be valved off from the main line con-nection to prevent leakage between the twosystems. If leaks occur in the pumping connec-tions to the three-way valves of a steering gearinstallation, the pump can be cut out with thevalve, and another pump cut in. If the three-wayvalves fail to cut out the leaking unit, and itbecomes necessary to cut out both pumps of asteering gear installation, the valves may beclosed at the ram cylinder. Since hydraulic systemswill work without pressure control, leaking pipesor cylinders of the pressure control can be cut outof the system for repair by closing the valves inthe lines where they join the main piping.Expansion lines and replenishment lines inhydraulic systems of older ships are seldom asource of leakage or breakage, since they are notunder any appreciable pressure; however, all con-nections must be maintained intact. In morerecent installations, however, replenishing linesare under pressure of as much as 300 psi. In theseinstallations, the hydraulic systems should not beoperated during repair of the lines.Relief valves and shuttle valves of a hydraulicsystem may also be a source of trouble. The seatsof relief valves which are leaking should bereground. Loss of power is a symptom of a leak-ing relief valve. Shuttle valves may stick and failto cut off; this condition is evidenced either bythe escape of oil from the high pressure side ofthe line into the expansion tank or by the failure7-19
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