problems.   The   two   most   common   casualties   that   you can   identify   just   by   noting   variations   in   the   system pressure  are  loss  of  pitch  control  and  loss  of  hydraulic oil   pressure. Loss  of  Pitch  Control A   loss   of   pitch   control   can   be   caused   by   either   a mechanical   or   an   electrical   failure.   Mechanical   failures tend  to  occur  more  frequently.  You  should  be  aware, however,   that   electrical   problems   can   occur   that   will occasionally   produce   a   loss   of   control.   Normally,   an electrical  problem,  such  as  a  broken  or  loose  cannon plug  or  loss  of  feedback  position,  will  require  the  system to  be  shifted  to  manual  control.  In  DDG-51  class  ships, however,   the   CPP   system   has   both   a   normal   and   an alternate   system   by   which   the   pitch   position   can   be monitored.   If   the   normal   system   fails   to   provide command   or   feedback   data,   the   CPP   system   can   be shifted   to   the   alternate   system.   When   investigating   a loss   of   pitch   control   on   any   gas   turbine-powered   ship, you  must  be  aware  of  the  components  in  the  CRP/CPP systems   that   are   most   likely   to   fail.   The   following   are some  of  the  components  you  will  have  to  monitor  most frequently. ELECTROHYDRAULIC   SERVO   VALVE.— The   most   common   component   failure   is   the electrohydraulic   servo   valve.   This   valve   is   the   primary component   for   remote   operation   and   control.   If   this valve  were  not  installed,  all  operations  would  require personnel  to  be  stationed  at  the  OD  box  at  all  times. You   can   easily   identify   a   faulty   electrohydraulic servo   valve.   Any   of   the   following   symptoms   should alert  you  as  to  the  possible  failure  of  this  valve: Pitch  fails  to  respond  to  a  desired  integrated throttle   control   (ITC)   change. Pitch   changes   (fluctuations)   occur   without   a pitch  change  command. Hub   servo   pressure   increases   steadily   without   a change   in   system   demands. AUXILIARY   RELIEF   VALVE.—   A   faulty auxiliary   relief   valve   also   will   cause   a   loss   of   pitch control.  If  the  valve  fails  in  the  open  position,  all  of  the control  oil  will  be  ported  back  to  the  sump.  Pitch  cannot be  changed  without  control  oil  to  position  the  auxiliary servo  piston  in  the  OD  box.  In  addition  to  the  loss  of pitch   control,   you   should   investigate   any   loss   of pressure.  You  should  be  able  to  spot  a  pressure  loss  by checking  the  HOPM  pressure  gauges.  This  should  be one  of  your  first  steps  in  checking  the  system. REDUCING   VALVE.—   A  faulty  reducing  valve  is another  cause  for  a  loss  of  pitch  control.  If  the  reducing valve  fails  in  the  closed  position,  the  flow  of  control  oil will  be  cut  off  to  the  auxiliary  servo  piston,  and  pitch will  fail  to  respond.  Like  the  auxiliary  relief  valve,  this loss  of  pressure  will  have  to  be  viewed  at  the  HOPM during   the   initial   system   investigation. Loss  of  Hydraulic  Oil  Pressure Usually,  a  loss  of  hydraulic  oil  pressure  will  cause an   alarm   to   be   generated   at   the   PACC/PCC.   The generation   of   this   alarm,   of   course,   will   immediately alert   the   operator   to   a   problem.   The   alarm   will   sound when  casualties  occur  either  to  the  main  relief  valve  or to  a  sequencing  valve.  The  alarm  may  or  may  not  sound, however,  when  a  major  leak  occurs.  Look  at  the  three main  causes  of  hydraulic  oil  pressure  loss  and  the resulting  alarms. MAIN  RELIEF  VALVE.—  A   faulty   main   relief valve  can  be  identified  by  a  low-pressure  alarm  at  the console,   but   the   actual   answers   can   be   found   at   the HOPM.  This  component  failure  can  be  easily  identified by  the  operator.  The  operator  simply  looks  at  the  HOPM pressure   gauges   and   notes   that   all   pressures   are extremely   low   or   nonexistent. SEQUENCING   VALVE.—   You  may  suspect  that  a sequencing  valve  is  faulty  after  a  loss  of  pitch  control  as well   as   a   loss   of   hydraulic   oil   pressure,   depending   on how  the  valve  fails.  For  instance,  if  the  valve  fails  in  the open   position,   then   all   the   oil   would   become high-pressure  oil  and  the  low-pressure  alarm  would  not sound.  In  this  case,  the  auxiliary  servo  supply  (control oil)   pressure   would   be   drastically   low   and   the   system control  would  fade.  On  the  other  hand,  if  the  sequencing valve  fails  in  the  closed  position,  a  low-pressure  alarm would  sound  and  alert  the  operator.  In  this  instance,  the operator  would  also  be  able  to  see  an  extremely  sluggish pitch   response   time. MAJOR  LEAK.—  A  major  leak  can  provide  the same   symptoms   as   a   loss   of   hydraulic   oil   pressure, depending  on  the  location  of  the  leak. We  have  just  told  you  about  some  of  the  components you  should  check  when  you  detect  a  loss  of  pitch  control or  a  loss  of  hydraulic  oil  pressure.  Now,  we  will  discuss some  of  the  most  common  maintenance  procedures  you as  a  supervisor  will  expect  your  personnel  to  perform. 3-17