Manitowoc Published 10-01-2012, Control # 045-08 1-53
777 SERVICE MANUAL INTRODUCTION
1
When the front drum is placed in free fall mode, the PC
closes a circuit to front drum clutch solenoid HS20. A path for
oil supply is opened from the front drum hoist charge pump
to clutch cylinder and the clutch is released disconnecting
the load drum from its drive motor.
Clutch opens when in free fall mode. When returning to or in
Standard, Luffing, or Clam Shell mode the clutch switch must
be closed to the PC for verification the clutch is engaged
before brakes can be released.
When front hoist control handle is in the off position, the PC
opens the circuit to the front hoist pump EDC and the front
hoist pump does not stroke.
Should a fault relating to the load drum occur while in free fall
mode, the clutch will re-engage load drum with its drive
motor and brakes apply.
Should charge pressure drop below 295 psi (20 bar) on the
low pressure side of the closed-loop while hoisting, power
lowering, or in free fall, the hydraulic park brakes begin to
apply. If pressure drops below 220 psi (15 bar), the park
brakes are fully applied.
WARNING
Dropping Load!
Apply working brake if a limit or operating fault occurs
while hoisting or power lowering.
Hoisted load will drop if working brake is not applied!
FIGURE 1-37
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