HOISTS MLC165-1 SERVICE/MAINTENANCE MANUAL
5-8
Published 05-26-17, Control # 238-02
Free Fall System (Optional)
Drum 1, Drum 2, or both drums can be equipped with the
free fall (FF) option. When FF is enabled, a large brake using
spring-applied, hydraulically released friction discs is used to
control the lowering of a load. Raising a load when FF is
enabled works the same as in normal operation.
NOTE When the crane is not in FF mode, depressing the
clutch/brake pedal has no effect on hoist operation.
The motor and motor brake used on the FF drum are the
same as are used on the non-free fall drum. The only
difference is that the motor supplied with the FF option does
not have a speed sensor. Drum speed is taken from an
external speed sensor assembly (See Speed Sensor—Free
Fall Drum on page 5-11).
Cooling oil flow through the brake is continuous whether or
not FF mode is enabled. Cooling oil flow (50 psi, 3.5 bar) is
provided by the FF cooling pump, which is dedicated for this
purpose.
During free fall operation, the accessory pump pressure is
limited to 1,000 psi (69 bar) by a pressure control valve on
the pump. Brake release pressure is reduced to 800 psi (55
bar) by a pressure compensator in the free fall pedals.
Figure 5-5. Drum Operation—Free Fall Mode
Drum Control Handle—Raise
Hoist Operates Normally
Drum Control Handle—Neutral
The load is controlled by the operator
using the clutch/brake pedal
Free fall brake is spring-engaged—
Brake shaft does not rotate, is
disconnected from drive gears.
Free fall brake can be
hydraulically released—
Brake shaft can rotate as the
clutch/brake is released. Brake
shaft is connected to drive gears.
Motor shaft disconnected from
drive gears
M10026
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