H Y D R A U L I C  S Y S T E M lever  is   moved  to  the  TILT   BACK   position,   the spring for the tilt control, beside spring (7) moves the roller into detent (6) which keeps the control lever in the  TILT  BACK  position. TM   5-3805-258-24-1 S Y S T E M S      O P E R A T I O N system. The oil then goes through lift and tilt control valve  (26)  because  both  valve  spools  are  in  HOLD position. The oil then goes through oil filters (29) and back  into  hydraulic  tank  (18).  If  oil  filters  (29)  get full  of  foreign  material  (debris),  filter  bypass  valve (28)  will  open  and  let  the  return  oil  go  directly  into the  hydraulic  tank. When   the   tilt   control   lever   is   moved   to   TILT BACK  position,  tilt  back  stem  (12)  moves  to  TILT BACK position. Pilot oil is now free togo through lift and tilt pilot valve (5) to the left end of tilt valve spool (13).  This  causes  the  tilt  valve  spool  to  move  to  the right. The pilot oil at the right end  of tilt valve spool (13) goes back to lift and tilt pilot valve (5), through C O N T R O L     L E V E R S     A N D     L I N K A G E I N     H O L D     P O S I T I ON 5.   Detent   for   lift   and   float.   6.   Detent   for   tilt   back.   7.   Spring (for    lift    detent    roller).    8.    Lift    kick    out    solenoid.    9.    Bucket positioner solenoid. TILT  CIRCUIT TILT BACK Operation When the engine is running with the control levers in HOLD position, pilot pump section (19) takes oil from  hydraulic  tank  (18)  and  sends  it  first  to  pilot section relief valve (17) which controls the maximum pressure  in  the  pilot  system.  The  pilot  oil  flow  then divides. Some oil goes through line (16) to the hand metering  unit  of  the  steering  system.  Some  oil  goes through  check  valve  (15)  and  selector  and  pressure control valve (10) to lift and tilt pilot valve (5). The valve stems in the pilot valve stop the flow of oil in HOLD position. The oil from pilot pump section (19) goes  through  pilot  section  relief  valve  (17)  through oil  filters  (29)  and  back  into  hydraulic  tank  (18). At   the   same   time,   steering   pump   section   (20) sends  oil  through  line  (23)  to  the  steering  control valve  of  the  steering  system.  Also,  implement  pump section (27) sends oil to main relief valve (4) which controls the maximum pressure in the implement oil dump   stem   (11)   and   on   to   hydraulic   tank   (18). The  movement  of  tilt  valve  spool  (13)  stops  the flow  of  oil  through  lift  and  tilt  control  valve  (26). Implement  pump  pressure  increases  and  opens  load check  valve  (9).  The  oil  from  implement  pump  sec- tion (27) now goes to the head end of tilt cylinder (1) and causes the cylinder piston and rod to extend. The Z-bar   linkage   causes   the   bucket   to   tilt   back.   The movement  of  the  cylinder  piston  and  rod  pushes  the oil  out  of  the  rod  end  of  the  tilt  cylinder.  This   oil comes  into  lift  and  tilt  control  valve  (26)  and  goes around  both  valve  spools  (13)  and  (22)  on  its  way back  to  oil  filters  (29)  and  hydraulic  tank  (18). There  is  a  detent  in  TILT  BACK  position  when the  bucket  is  between  DUMP  position  and  the  cor- rect  angle  to  dig.  This  detent  holds  the  tilt  control lever  [and  tilt  back  stem  (12)]  in  TILT  BACK  posi- tion until the bucket gets to the correct angle to dig. When the bucket gets to the correct angle, the bucket positioner releases the tilt control lever and the lever and  tilt  back  stem  (12)  go  back  to  HOLD  position. The  flow  of  pilot  oil  through  lift  and  tilt  pilot  valve (5)  is  stopped.  The  springs  on  tilt  valve  spool  (13) move  the  valve  spool  back  to  HOLD  position.  The pilot oil at the left end of the tilt valve spool goes back to  lift  and  tilt  pilot  valve  (5),  through  tilt  back  stem (12)  and  on  to  hydraulic  tank  (18).  The  implement oil in tilt cylinder (1) is held by tilt valve spool (13) and  movement  of  the  cylinder  piston  and  rod  stops. The bucket will stay at the correct angle to dig until the  tilt  control  lever  is  moved  again.  There  is  no detent  from  the  digging  angle  to  tilt  back.  The  con- trol  lever  must  be  held  in  TILT  BACK  position  to move  the  bucket  farther. See FO-1, STANDARD HYDRAULIC SYSTEM IN TILT BACK POSITION, located in the back of this manual. 3-111