Chapter  7—AUXILIARY  MACHINERY On some modern hydraulic transmissions, the SHAFT STUFFING BOX PACKING is of the square-braided  pure  asbestos  type.  This  packing is  easily  removed,  but  care  must  be  taken  to ensure that it is not replaced too tightly. If prop- erly installed, this packing makes a tight joint when  you  apply  light  pressure.  If  packing  wears out  quickly,  the  shaft  should  be  inspected  for roughness. If a lathe is available, roughness may be eliminated from a shaft by a finishing cut to smooth the surface. If a lathe is not available, it may be necessary to replace the shaft. Packing should  be  renewed  at  prescribed  intervals  to eliminate the possibility of the packing becoming hard and scoring the shaft. When packing is be- ing replaced, make certain that there is a uniform thickness around the shaft. An excess of packing on one side of the shaft will cause shaft deflec- tion  and  may  cause  breakage.  Stuffing  boxes should  be  packed  loosely  and  the  packing  gland set up lightly to allow adequate leakage for cool- ing and lubrication. There will be very little likelihood of poor alignment   between   the   driving   and   driven members   of   a   hydraulic   transmission   if   the wedges,    shims,   jacking   screws,   or   adjusting setscrews are properly set and secured when con- necting  units  are  installed.  However,  when  a casualty occurs or a unit is replaced, it is possi- ble for units to get out of alignment sufficiently to  cause  severe  stress  and  strain  on  the  coupling and  connected  parts.  Excessive  misalignment should be eliminated as soon as possible by replac- ing  any  defective  parts  and  by  readjusting  the aligning devices.    If   this   is   not   done,   pins, bushings, and bearings will wear out too fast and will have to be replaced frequently. Since there is no end play to either the pump shaft or the motor shaft, flexible couplings are generally used in hydraulic transmissions. Such couplings  permit  satisfactory  operation  with  a slight misalignment, without requiring frequent renewal of parts. Piping and Fittings If properly installed, the piping and valves of a   hydraulic   system   are   seldom   a   source   of trouble,  except  for  leakage.  Since  some  leaks, however, can be of sufficient seriousness to cause a reduction in the efficiency of the unit, frequent inspections should be made for leakage and steps should  be  taken  to  eliminate  any  leakage  found. If leaks occur at a flanged joint in the line of a  hydraulic  system,  tighten  the  flange  bolts evenly, but not excessively. If the leaks persist, use the auxiliary gear while the leaking flange is being refitted with copper asbestos or "O" ring packing.  Be  sure  the  flange  surfaces  are  cleaned carefully before the packing is applied. CAUTION: Exposure to asbestos fibers is a recognized  health  hazard.  Refer  to  N.S.T.M. chapter 635 for safety requirements applicable to handling asbestos packing and gaskets. Operation  of  hydraulic  equipment  may  be continued while leakage repairs are being made in some parts of the system if certain measures are taken. When lines in an auxiliary system leak, they should be valved off from the main line con- nection  to  prevent  leakage  between  the  two systems. If leaks occur in the pumping connec- tions to the three-way valves of a steering gear installation,  the  pump  can  be  cut  out  with  the valve, and another pump cut in. If the three-way valves  fail  to  cut  out  the  leaking  unit,  and  it becomes necessary to cut out both pumps of a steering  gear  installation,  the  valves  may  be closed at the ram cylinder. Since hydraulic systems will work without pressure control, leaking pipes or cylinders of the pressure control can be cut out of the system for repair by closing the valves in the lines where they join the main piping. Expansion lines and replenishment lines in hydraulic  systems  of  older  ships  are  seldom  a source of leakage or breakage, since they are not under any appreciable pressure; however, all con- nections  must  be  maintained  intact.  In  more recent installations, however, replenishing lines are under pressure of as much as 300 psi. In these installations, the hydraulic systems should not be operated during repair of the lines. Relief valves and shuttle valves of a hydraulic system may also be a source of trouble. The seats of  relief  valves  which  are  leaking  should  be reground. Loss of power is a symptom of a leak- ing relief valve. Shuttle valves may stick and fail to cut off; this condition is evidenced either by the escape of oil from the high pressure side of the line into the expansion tank or by the failure 7-19