H Y D R A U L I C  S Y S T E M TM   5-3805-258-24-1 S Y S T E M S  O P E R A T I O N When the engine is off and the lift arms are raised, check valve (4) will permit pressure oil from the head end  of  the  lift  cylinders  to  go  to  the  selector  and pressure  control  valve  for  operation  of  pilot  valves. Check valve (2) will not let the oil from the head end of  the  lift  cylinders  go  into  the  pilot  pump  section. Pressure  oil  at  inlet  passage  (6)  pushes  valve  (7) against spring (8). The oil is then free to go through holes  (9)  in  valve  (7)  and  out  outlet  passage  (10). Pressure  oil  at  outlet  passage  (10)  pushes  against valve (7) and holds it closed. No oil can flow through the check valve. SELECTOR AND PRESSURE CONTROL VALVE The  selector  and  pressure  control  valve  is  in  the pilot  oil  system.  It  sends  oil  to  the  lift  and  tilt  pilot valve   for   its   operation.   The   selector   and   pressure control valve makes pressure oil available to the pilot valve  to  lower  a  raised  bucket  (lift  arms)  when  the engine is off. S E L E C T O R      A N D      P R E S S U R E      C O N T R O L      V A L V E 1.    Drain    passage.    2.    Spacers.    3.    Spring.    4.    Holes    (four).    5. I n l e t    p a s s a g e    f r o m    h e a d    e n d    o f    l i f t    c y l i n d e r s .    6 .    V a l ve spool.   7.   Inlet   passage   from   pilot   pump   section.   8.   Holes (two).    9.    Outlet    passage    to    lift    and    tilt    pilot    valve. During normal operation, pressure oil from the pilot pump section goes through inlet passage (7). The pressure of this oil is controlled by the pilot relief valve. This oil goes through holes (4) in valve spool  (6), through the center of the valve spool and out outlet passage (9) to the lift and tilt pilot valve. This oil can not go through holes (8) and out inlet passage (5). There is a check valve in this line to stop the flow of oil to the head end of the lift cylinders. When the engine is off, there is no pressure oil at inlet passage (7). When the engine is off and the lift arms are raised, the pressure from the head end of the lift cylinders is in inlet passage (5). This oil is stopped (held) in the lines as long as the lower stem in the lift and tilt pilot valve is in the HOLD position. When the lower stem is moved to LOWER position, the pressure oil from the head end of the lift cylinders can now go through holes (8) in valve spool (6), through outlet passage (9), the pilot valve, and on to the lift valve spool in the lift and tilt control valve. The lift valve spool moves to LOWER position and the lift the lift arms will lower. A check valve in the line from inlet passage (7) will not let oil go to the pilot pump section. NOTE:  When  the  engine  is  off  and  the  lift  arms  are raised,  the  bucket  can  also  be  dumped. When  the  engine  is  off,  valve  spool  (6)  also  con- trols the pressure of the oil from inlet passage (5) to the  pilot  valve  [approximately  1030  kPa  (150  psi)]. When  the  pressure  through  outlet  passage  (9)  gets too  high,  the  pressure  will  cause  valve  spool  (6)  to move  against  the  force  of  spring  (3).  This  decreases the flow of oil through holes (8) in the valve spool and decreases  the  pressure  in  outlet  passage  (9). LIFT AND TILT PILOT VALVE The  lift  and  tilt  pilot  valve  is  controlled  manually by the operator. It sends oil from the pilot system to the lift and tilt control valve which controls the oper- ation  of  the  lift  and  tilt  cylinders.  There  are  four valve stems (of the pressure metering type) in the lift and  tilt  pilot  valve.  Two  valve  stems  are  needed  for each  operation  of  lift  and  tilt. When  a  lift  or  tilt  control  lever  is  moved,  one plunger  is  pushed  down  in  the  pilot  valve.  The plunger causes a valve stem to move down and send pilot oil to one end of a valve spool in the lift and tilt control valve. The valve spool then moves and pushes oil, from the opposite end of the valve spool, out of the lift  and  tilt  control  valve.  The  oil  goes  back  to  the pilot valve to another valve stem. The oil then goes to drain  through  tank  passage  (11). Three of the valve stems in the pilot valve are the same:  dump  stem,  tilt  back  stem  and  lift  stem  (13). Lower stem (12) is longer than the other three stems. All  four  stems  are  held  in  place  the  same  way. HOLD Position Of Lift Operation When  the  lift  control  lever  is  in  HOLD  position, plungers  (3)  and  (4)  are  in  the  same  position  (as shown).  The  plungers  do  not  push  up  against  actua- tor (1) in the hold position. Pressure oil from the pilot pump section goes through pump passage (20) and is stopped by the position of stems (12) and (13). Holes (14)  and  (15)  are  open  to  tank  passage  (11). 3-95