on  each  face  of  the  piston  is  balanced. Removing  the  oil  signal  from  the  valve  rod actuator stops motion in the valve rod and the hub servomotor. The self-centering feature of the servomotor over the regulating valve pin provides the   restoring   force   to   counteract   any hydrodynamic  tendency  to  change  pitch  from  that set by the command signal. INSPECTIONS The  inspections  mentioned  here  are  the minimum   requirements   for   reduction   gears. Where defects are suspected, or operating condi- tions so indicate, inspections should be made at more frequent intervals. No inspection plates or other fittings of the main reduction gear may be opened without the permission of the engineer officer. Before replac- ing  of  an  inspection  plate,  connection,  fitting,  or cover which permits access to the gear casing, make  a  careful  inspection  to  ensure  that  no foreign matter has entered or remains in the cas- ing or oil lines. An entry of the inspections, and the name of the CPO or officer who witnesses the closing of the inspection plate, should be made in the Engineering Log. PMS INSPECTIONS The  PMS  requirements  discussed  in  this  sec- tion are general in scope. Inspection requirements for your ship are listed in the ship’s PMS Manual and  should  be  referred  to  for  all  maintenance action. Gears   should   be   jacked   DAILY—AT ANCHOR—so   that   the   main   gear   shaft   is moved  1  1/4  revolutions.  This  jacking  should  be done with lubricating oil circulating in the system. You   should   take   the   following   actions QUARTERLY: 1. Sound with a hammer the holding down bolts, ties, and chocks to detect signs of loosen- ing of casing fastenings. 2.  Open  inspection  plates,  inspect  gears,  and oil-spray nozzles. Wipe off oil at different points and note whether the surface is bright or if already corroded,  and  whether  or  not  new  areas  are affected. 3.   Inspect   the   strainers   for   the   oil-spray nozzles  to  see  that  dirt  or  sediment  has  not accumulated in them. 4.  Take  and  record  all  main  thrust  bearing readings. When  conditions  warrant  or  if  trouble  is suspected, a work request should be submitted to a naval shipyard to perform a 7-YEAR INSPEC- TION of the main reduction gears. This inspec- tion  includes  clearance  readings  of  bearings  and journals; alignment checks and readings; and any other inspections, tests, or maintenance work that may  be  considered  necessary. If  the  ship’s  propeller  strikes  ground  or  a submerged object, a careful inspection should be made  of  the  main  reduction  gear  immediately following the OCCURRENCE of the casualty. In this  inspection,  the  possible  misalignment  of  the bull  gear  and  its  shaft  should  be  considered. Where practicable, a naval shipyard should be re- quested to check the alignment and concentricity of the bull gear. NAVAL  SHIPYARD  OVERHAUL During  a  naval  shipyard  overhaul,  the  fol- lowing  work  should  be  performed:  inspection  of the condition and clearance of thrust shoes to en- sure proper position of gear; inspection of the thrust collar, nut, and locking device; and inspec- tion of the flexible couplings between turbines and reduction  gears  and  removal  of  the  sludge deposits. FULL POWER TRIALS The  correction  of  any  defect  disclosed  by regular tests and inspections, and the conscien- tious observance of the manufacturers’ instruc- tions, should assure that the gears are ready for full power at all times. It  is  not  advisable  to  open  up  gear  cases, bearings,   and   thrusts   immediately   BEFORE TRIALS.  In  addition  to  the  inspections  which may be directed by proper authority which are conducted during the FULL POWER TRIALS, the  following  checks  must  be  made  AFTER TRIALS. Open the inspection plates, and examine the tooth contact and the condition of the teeth to note changes that may have occurred during Chapter  4—REDUCTION  GEARS  AND  RELATED  EQUIPMENT 4-15