INTRODUCTION 999 SERVICE/MAINTENANCE MANUAL
1-50
Published 05-16-17, Control # 233-03
Mast System
See Figures 1-36 and 1-37
When in Crane Setup mode, mast-raising sequence is
controlled by the PC. Mast raising and lowering rate is
controlled by engine speed, as it regulates pay out and haul
in of the cable reeving between gantry and mast sheaves.
Mast raising cylinders also provide assistance to lift and
lower mast during reeving of the mast and gantry sheaves.
A mast operating limit message MAST TOO FAR FWD
appears on the digital display screen when the mast is
lowered to 175°. The PC detects this fault when mast angle
indicator monitors the mast position at 175° and overrides
boom down command to automatically stop the boom from
lowering. It is not possible for the operator to boom down at
this time, and boom should be raised to correct this fault.
Mast switch (2), on front console, should only be used for
raising/lowering mast cylinders without wire rope rigging.
When top of mast switch is pressed and held in the raise
position, the PC sends an output signal to mast cylinders
raise solenoid HS-1. When bottom of mast switch is pressed
and held in the lower position, the PC sends an output signal
to mast cylinders lower solenoid HS-2.
Mast accessory valve is “motor spool” where both cylinder
ports and tank port of the valve spool section are connected
in center position. This type of spool prevents premature
opening of equalizing valves (8). Hydraulic pressure for mast
cylinder solenoids HS-1 and HS-2 is from rear drum low-
pressure side closed-loop system.
When raising the mast, the PC monitors boom hoist drum
speed with the boom hoist drum encoder (3). The PC
maintains a speed that is proportional to accessory system
hydraulic pressure applied to the mast cylinders. The desired
accessory system pressure builds with the actual pressure
between a minimum of 500 psi (34 bar) at the beginning and
3000 psi (207 bar) after the mast starts moving.
When lowering the mast, the PC monitors boom hoist
hydraulic system with boom hoist pressure sender (12). The
PC maintains a minimum rope tension on boom hoist drum.
The PC maintains this tension by controlling boom hoist
pump to create an average system pressure of
approximately 1100 psi (76 bar). The accessory system
hydraulic system is maintaining a minimal hydraulic pressure
by taking advantage of the boom hoist rope tension and the
weight of the mast to retract the cylinders.
Each mast raising cylinder (6) has a counterbalance valve
(7) at each cylinder port. These valves ensure smooth
control when raising or lowering gantry and locks the cylinder
in place when gantry is at a desired position or if a hydraulic
line fails.
CAUTION
Mast bypass valve (5), in right side enclosure, must be
turned to ON position during crane setup (assembly and
disassembly). Mast bypass valve must be turned to OFF
position during normal operation to prevent mast arms
from raising and contacting mast.
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