conditions that lead to additional trouble, since dirt may enter an open system. Leaks are a frequent cause of trouble in hydraulic equipment. Generally, leaks are a result of excessively worn  parts,  abnormal  and  continuous  vibration, excessively   high   operating   pressures,   or   faulty   or careless  assembly.  External  leaks  usually  have  little effect on the operation of equipment other than a steady draining of the oil supply. Even a small leak wastes oil, and the resulting unsightly appearance of a machine is indicative of poor maintenance procedures. External   leaks   may   result   from   improperly tightened threaded fittings; crossed threads in fittings; improperly   fitted   or   damaged   gaskets;   distorted   or scored sealing rings, oil seals, or packing rings; scored surfaces of working parts; improperly flared tube ends; or  flanged  joints  not  seating  squarely. Internal  leaks  usually  result  in  unsatisfactory operation  of  the  equipment.  Large  internal  leaks  are signified   by   a   loss   of   pressure   and   the   failure   of equipment.  While  large  internal  leaks  can  usually  be located by installing pressure gauges in various parts of the  equipment,  the  location  of  small  leaks  generally requires disassembly and visual inspection of the parts. Internal leaks may result from worn or scored valves, pistons, valve plates or bushings, or improperly fitted or damaged  gaskets. The  most  common  symptom  of  trouble  in  a hydraulic system is an unusual noise. Some noises are characteristics  of  normal  operation  and  can  be disregarded,  while  others  are  evidence  of  serious trouble.  Even  though  the  exact  sound  indicating  a specific trouble can be learned only through practical experience, the following descriptive terms will give a general idea of which noises are trouble warnings. If   popping   and   sputtering   noises   occur,   air   is entering the pump intake line. Air entering the system at this point may be the result of too small an intake pipe, an air leak in the suction line, a low oil level in the supply tank, cold or heavy oil, or possibly the use of improper oil. If   air   becomes   trapped   in   a   hydraulic   system, hammering  will  occur  in  the  equipment  or  transmission lines.  When  this  occurs,  check  for  improper  venting. Sometimes, a pounding or rattling noise occurs as the result of a partial vacuum produced in the active fluid during  high-speed  operation  or  when  a  heavy  load  is applied.  This  noise  may  be  unavoidable  under  the conditions stated and can be ignored if it stops when speed  or  load  is  reduced.  If  the  noise  persists  at  low speeds or light loads, the system needs to be vented of air.  Air  in  a  hydraulic  system  can  also  cause  uneven motion of the hydraulic motors. When  a  grinding  noise  occurs,  it  can  usually  be traced to dry bearings, foreign matter in the oil, worn or scored parts, or overtightness of some adjustments. The  term  hydraulic  chatter  is  sometimes  used  to identify  noises  caused  by  a  vibrating  spring-actuated valve, 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 too tight around some moving part or that a high-frequency vibration is occurring in a relief valve. Electrical  Troubles Even   though   troubles   occurring   in   electrical equipment  are  the  responsibility  of  the  Electrician’s Mate, the Engineman can help maintain the equipment by making a few simple checks when electrical troubles occur. Failure to have a switch in the ON position will cause  unnecessary  delay  in  operating  electrical equipment. If the switch is closed and the equipment still fails to operate, check for blown fuses or tripped circuit breakers. Troubles of this type are usually the result of an  overload  on  the  equipment.  If  a  circuit  breaker continues  to  cut  out,  the  trouble  may  be  caused  by damaged  equipment,  excessive  binding  in  the  hydraulic transmission  lines,  or  faulty  operation  of  the  circuit breaker. Check for visual indication of open or shorted leads,  faulty  switches,  or  loose  connections.  Do  not make repairs to the electrical equipment or system. Do not  open  enclosures  of  electrical  equipment,  but  do report  evidence  of  possible  electrical  failure  to  the Electrician’s   Mate. Mechanical  Troubles When   electrohydraulically   driven   auxiliary machinery  becomes inoperative   because   of   a mechanical failure, a check should be made. Look for improper  adjustment  or  misalignment  of  parts;  shearing of  pins  or  keys;  or  breakage  of  gearing,  shafting,  or linkage.  Elimination  of  these  causes  should  be  done according  to  the  manufacturer’s  instructions  for  the specific  piece  of  equipment. MAINTENANCE The  principal  requirements  necessary  to  keep  a hydraulic  transmission  in  satisfactory  operating condition are regular operation, proper lubrication, and 8-7