TM10-3930-660-34 The variable displacement, axial-piston pump supplies oil flow for the MLRS valve which controls fork, carriage, and MLRS attachment  functions.    The  piston  pump  also  supplies  oil  flow  to  the  hydraulic  joystick  through  the  shuttle  valve.    The shuttle valve closes the port from the emergency steer pump during normal piston pump operation. The  piston  pump  utilizes  specifically  designed  control  valves  which  is  the  "brain"  of  the  piston  pump  and  its  related hydraulic functions.  The valves control delivery of oil flow and pressure in amounts only as required by the function that is operated.  Both flow and pressure are tailored to the specific load.  All adjustments by the control valves occur in fractions of a second. When functions of the MLRS valve are idle, the pump is in "stand-by" mode.  The load sensing line from the MLRS valve senses  no  load  (zero  pressure).  Therefore,  pump  output  pressure  is  controlled  only  by  spring  force  of  the  compensator (low pressure) spool spring.  The pump will continue its low output until the spring force of the compensator is overcome by the load sensing pressure.  Oil from the compensator spool holds the swash plate to near vertical position.  The pump is  allowed  to  supply  only  enough  oil  flow  to  meet  normal  MLRS  valve  leakage  and  output  pressure  is  maintained  at approximately 400 psi (2758 kPa). When one or more of the MLRS valves are actuated, the pump goes into "pumping" mode.  The load sensing line from the MLRS   valve   is   pressurized   by   the   function   experiencing   the   highest   pressure.      This   pressure   is   fed   back   to   the compensator  spool.    The  pump  continues  its  output  until  the  load  sensing  pressure  overcomes  the  compensator  spool spring force.  Oil from the compensator spool moves the swash plate to an angle that will provide the pump with an output equal to the load sense pressure plus approximately 400 psi (2758 kPa).  Therefore the pump will supply only enough flow and pressure to perform the function(s). The pump is in "maximum high pressure" mode when load sensing line pressure reaches approximately 3000 psi (20685 kPa).  The high pressure spool compresses the spring and allows oil to move the swash plate to near vertical position.  Oil flow  from  the  compensator  spool  is  stopped  and  now  the  pump  will  supply  oil  flow  to  meet  circuit  leakage  and  output pressure is maintained at approximately 3000 psi (20685 kPa). The  piston  pump  is  connected  to  the  reservoir  so  any  additional  oil  required  is  readily  available.    Any  by-pass  oil  in  the pump can be returned to the reservoir through the drain line. Return oil from the main valve, steering valve, relief valve of the priority valve, brake valve, and relief valve passes through the hydraulic filter before entering the reservoir.  The filter is equipped with a bypass which has a visual indicator showing when bypass is occurring. b. Frame  Tilt  System.    The  frame  tilt  valve  has  three  operating  positions,  tilt  right,  tilt  left,  and  hold.    The  center position is the hold position. With the frame tilt valve lever in the hold (center) position, the hydraulic oil is trapped in the cylinder and lines.  The cylinder cannot move.  Oil flow from the brake valve, which originates from the small section of the gear pump, continues 16-4