TM   5-3805-258-24-1 H  Y  D  R  A  U  L  I  C   S  Y  S  T  E  M S  Y  S  T  E  M  S      O  P  E  R  A  T  I  O N When   the   attachment   (third)   control   lever   is moved   to   CLOSE   or   LOWER   position,   close   or lower   stem   (36)   moves   to   CLOSE   or   LOWER position.  Pilot  oil  is  now  free  to  go  through  attach- ment pilot valve (33) to the right end of attachment valve   spool   (31).   This   causes   the   valve   spool   to move  to  the  left.  The  pilot  oil  at  the  left  end  of attachment   valve   spool   (31)   goes   through   shuttle valve   (40),   back   to   attachment   pilot   valve   (33), through  open  or  raise  stem  (37)  and  onto  hydraulic tank  (18). The   movement   of   attachment   valve   spool   (31) stops   the   flow   of   oil   through   attachment   control valve  (38).  Implement  pump  pressure  increases  and opens load check valve (32). The oil from implement pump   section   (27)   now   goes   to   the   head   end   of attachment  cylinders  (30)  and  causes  the  cylinder pistons  and  rods  to  extend.  The  movement  of  the cylinder  pistons  and  rods  pushes  the  oil  out  of  the rod  end  of  the  attachment  cylinders.  This  oil  comes into  attachment  control  valve  (38)  and  goes  around all three valve spools (31), (13) and (22) on its way back  to  oil  filters  (29)  and  hydraulic  tank  (18). When  the  pressure  of  the  oil  to  the  head  end  of the   attachment   cylinders   gets   to   approximately 15500  kPa  (2250  psi),  the  spool  of  sequence  valve (39)  moves  up.  This  causes  oil  from  close  or  lower stem  (36)  to  go  through  sequence  valve  (39)  and shuttle  valve  (40)  to  the  left  end  of  attachment valve   spool   (31).   The   springs   on   the   attachment valve  spool  cause  it  to  move  to  HOLD  position. Implement  pressure  oil  to  the  attachment  cylin- ders  is  now  stopped. When  the  pressure  of  the  oil  to  the  head  end  of the  attachment  cylinders  gets  below  approximately 12400 kPa ( 1800 psi), the spool of sequence valve (39)  moves  down.  This  stops  the  flow  of  pilot  oil to  the  left  end  of  attachment  valve  spool  (31).  The valve   spool   again   moves   to   the   left   (CLOSE   or LOWER  position)  and  implement  pressure  oil goes  to  the  attachment  cylinders. See FO-5, STANDARD HYDRAULIC SYSTEM IN LOWER POSITION (ENGINE OFF), located in the back of this manual. The  operation  of  sequence  valve  (39)  and  shuttle valve  (40)  permits  the  operation  of  the  lift  and  tilt circuits   during   CLOSE   or   LOWER   operation. There  are  no  detents  on  the  attachment  control. When  the  attachment  control  lever  is  released,  the lever, close or lower stem (36) and attachment valve spool  (31)  go  back  to  HOLD  position.  The  cylinder pistons  and  rods  are  stopped  and  will  stay  in  this position until the attachment control lever is moved again. OPEN or RAISE Position When  the  attachment  control  lever  is  moved  to OPEN  or  RAISE  position,  open  or  raise  stem  (37) moves to OPEN or RAISE position. Pilot oil is now free  to  go  through  attachment  pilot  valve  (33)  and shuttle valve (40) to the left end of attachment valve spool (31). This causes the valve spool to move to the right.  The  pilot  oil  at  the  right  end  of  attachment valve spool (31) goes back to attachment pilot valve (33),  through  close  or  lower  stem  (36)  and  on  to hydraulic  tank  (18). The   movement   of   attachment   valve   spool   (31) stops   the   flow   of   oil   through   attachment   control valve  (38).  Implement  pump  pressure  increases  and opens load check valve (32). The oil from implement pump  section  (27)  now  goes  to  the  rod  end  of attachment  cylinders  (30)  and  causes  the  cylinder pistons  and  rods  to  retract.  The  movement  of  the cylinder  pistons  and  rods  pushes  the  oil  out  of  the head end of the attachment cylinders.  This oil comes into  attachment  control  valve  (38)  and  goes  around all  three  valve  spools  on  its  way  back  to  oil  filters (29)  and  hydraulic  tank  (18). When   the   attachment   control   lever   is   released, the  lever,  open  or  raise  stem  (37)  and  attachment valve  spool  (31)  go  back  to  HOLD  position.  Move- ment  of  the  cylinder  pistons  and   rods   is   stopped until  the  attachment  control  valve  is  moved  again. See FO-7, OPTIONAL HYDRAULIC SYSTEM IN CLOSE OR LOWER POSITION, located in the back of this manual. 3-114