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.
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