TM   9-2350-256-34-2 Section  III.  GENERAL  MAINTENANCE 2 - 7 . Installing  Lock  Wire Locking  wire  is  to  be  installed method. by  the  double  twist 2-8. Application   of   Sealing   Compounds Application  of  sealing  compound  to  pipe  threads  is specified   in   applicable   sections   of   this   manual. 2-9. Lubrication R e f e r   t o   T M   9 - 2 3 5 0 - 2 5 6 - 1 0   a n d   T M   9 - 2 3 5 0 - 256-20   for   detailed   lubrication   instructions c o v e r i n g   t h e   c o m p o n e n t s   o f   t h e   R e c o v e r y Vehicle. 2 - 1 0 . Maintenance   and   Operation   of   Main Hydraulic   System a.   General.   The   main   hydraulic   system   powers and  controls  the  main  winch.  hoist  winch,  hoisting boom  and  spade.  The  main  winch  and  hoist  winch are  driven  by  vane-type  hydraulic  motors,  and  the hoisting  boom  and  spade  are  actuated  by  hydraulic cylinders.   Hydraulic   fluid,   under   pressure   for   op- erating   the   hydraulic   motors   and   hydraulic   cylin- ders,  is  provided  through  a  closed  power  circuit  by a  fixed-displacement,  vane-type,  double  pump  driv- en  by  a  mechanical  transmission  (power  takeoff) from   the   main   engine.   The   hydraulic   pump   draws its   fluid   from   the   hydraulic   oil   tank,   and   pump output  is  controlled  by  engine  speed.  The  operation of  the  hydraulic  motors  and  the  hydraulic  cylinders is  controlled  through  the  control  circuit.  Each  winch hydraulic   motor   is   provided   with   a   pilot-operated, spring-centered,  directional  combination  control valve   which   directs   the   fluid   in   the   power   circuit to  the  winch  being  operated.  These  directional  con- trol   valves   are   remotely   controlled   by   manually operated  hydraulic  control  valves,  which  direct  con- trol   pressure   to   them.   The   directional   combination control   valves   for   the   spade   and   boom   cylinders are   manually   controlled.   Any   internal   leakage through   the   hydraulic   motors,   cylinders,   or   valves is  returned  to  the  hydraulic  oil  tank  by  tank  return. Description   of   operation   of   the   basic   circuits   in the  main  hydraulic  system  will  be  found  in  sub- paragraphs  b  through  j  below.  Schematic  diagrams of  the  main  hydraulic  system  idling,  and  the  hydrau- lic   system   operating   the   main   winch,   hoist   winch, hoisting  boom,  and  spade  are  shown  in  figures  FO-1 through   FO-9. NOTE Refer  to  TM  9-2350-256-10  for  operating  in- structions   for   the   winches,   power   takeoff, and  hoist  system. b.   Main   Hydraulic   System-Idling   (Fig.   FO-1). With   the   main   engine   operating   at   system   idling speed,  the  power  control  valve  is  placed  in  the  ON position,   directing   mechanical   transmission   pump pressure  to  the  clutch  (port  no.  228),  thus  engag- ing  the  clutch  which  permits  the  mechanical  trans- mission  to  drive  the  main  hydraulic  pump.  The pump   draws   filtered   fluid   from   the   hydraulic   oil tank   (port   no.   69)   and   discharges   it   through   two outlet   ports   (port   nos.   1   and   44)   under   pressure. The  pump  discharge  pressure  is  directed  to  the  re- lief  and  unloading  valve  (port  no.  2)  and  the  hoist winch   combination   control   valve   (port   no.   27). Pump  discharge  pressure  passes  through  the  relief and   unloading   valve,   (port   no.   3)   through   the hydraulic  subplate  (port  nos.  136  and  125)  of  the main   hydraulic   control   panel,   and   to   the   system selector  valve  (port  no.  45)  which  is  placed  in  the MAIN position. The pump pressure is then directed to, and blocked at the spade and boom cumbination control   valves   (port   no.   33),   as   they   are   in   their normal  spring-centered  HOLD  position.  Differential pressure across the pilot pressure valve, in the main relief  valve,  forces  the  valve  open  to  allow  a  paral- lel   flow   (port   no.   4)   of   pump   discharge   pressure to  be  directed  to  the  hoist  winch  combination  con- trol  valve  (port  no.  22).  Differential  pressure  across the  pilot  pressure  valve,  in  the  hoist  winch  combi- nation  control  valve,  forces  the  valve  open,  direct- ing  the  pump  pressure  (port  no.  20)  to  the  main winch  combination  control  valve  (port  nos.  12  and 13),   where   the   action   duplicates   the   hoist   winch combination  control  valve  and  the  hydraulic  fluid is  returned  to  the  oil  tank  (port  no.  11).  Hydraulic pressure   is   directed   to   both   sides   of   the   winch motors  (port  nos.  17  and  18)  by  the  spring-centered directional  control  valve  in  the  winch  combination control   valves. c.  Main  Winch-Payout  (Fig.  FO-2).  With  the main  winch  control  valve  placed  in  the  PAYOUT position,  the  pilot  pressure  (port  nos.  15  and  16) tends   to   equal   pump   discharge   pressure   and   is directed   to   both   ends   of   the   pilot-operated   direc- tional control valve (port nos. 8 and 10) in the main winch  combination  control  valve.  The  ends  of  the directional   control   valve   differ   in   size,   the   larger end   at   port   no.   10   and   the   hydraulic   differential across   the   valve   causes   it   to   move,   directing   the flow  of  pump  pressure  to  one  side  of  the  main winch   motor   (port   no.   18),   causing   the   motor   to drive   the   main   winch   in   the   PAYOUT   direction. The pilot pressure is also directed to the main winch brake  cylinder  to  disengage  the  winch  brake.  Pump Change 7 2-23