INTRODUCTION 999 SERVICE/MAINTENANCE MANUAL
1-22
Published 05-16-17, Control # 233-03
When boom hoist brake switch is placed in off - park position,
boom hoist brake remains spring-applied to boom hoist drum
until the PC releases the brake. Boom hoist drum pawl out
solenoid HS-15 is enabled to disengage pawl from boom
hoist drum. Boom control handle circuit to PC remains open.
Boom Hoist Raise
When boom hoist handle (1) is moved back for booming up,
the handle neutral switch closes, sending an input voltage of
5 volts or more to PC. The PC sends a positive output
voltage to boom hoist system pump EDC (3) and a positive
output voltage to motor PCP (11). Boom up limit switch (12)
must closed and with no hydraulic system faults present.
The PC requires that boom hoist pump strokes in up
direction to satisfy pressure memory. The PC compares
boom hoist-holding pressure to value stored in pressure
memory. When system pressure is high enough, the PC
sends a positive output signal to enable brake release
solenoid HS-13. Brake release solenoid HS-13 shifts to block
tank port and open port from low-pressure side of closed-
loop system to release spring-applied brake.
The PC sends a positive output voltage to enable boom hoist
pump EDC that tilts pump swashplate to stroke pump in the
up direction. Hydraulic fluid flows from hoist pump port A to
port B of hoist motor (13). Fluid from motor port A, returns to
boom hoist pump port B.
The PC controls raising speed by varying the voltage to
pump EDC and motor PCP in relation to handle movement.
As boom hoist handle is moved back, the PC sends a signal
to increase the boom hoist pump swashplate angle. The PC
FIGURE 1-14
HS-14
.06
X
X
6 GPM
B
A
A
B
SERVO PRESSURE
CHARGE PUMP
LOW PRESSURE SIDE
HIGH PRESSURE SIDE
350 PSI
(24 BAR
)
HS-13
BOOM HOIST
DRUM
LOW PRESSURE
HS-15
BRAKE
PAWL
SUPERCHARGE
MANIFOLD
CHARGE
PUMP
FROM TRAVEL
PILOT
BOOM
HOIST
BOOM HOIST PUMP
999CSM1-113
3
5
3
9
3
6
3
2
3
4
3
13
3
10
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