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GENERAL DESCRIPTION:
The PULLMASTER Model M75 is a planetary hydraulic winch with reversing speeds 4.1 times faster than forward
speed. The main components of this unit are:
✛ hydraulic gear motor
✛ multi disc brake with static and dynamic function
✛ primary planet reduction
✛ secondary planet reduction
✛ final planet reduction
✛ brake housing
✛ final drive housing
✛ cable drum
FUNCTION IN FORWARD ROTATION (HOISTING):
In forward rotation, or when the winch is pressurized for hoisting, the output torque and rpm of the hydraulic motor
are transmitted to the sungear of the primary planet reduction. The output torque and rpm of the primary reduction
stage are transmitted to the secondary reduction stage by the secondary sungear, which is splined to the primary
planet hub. The final sungear is splined to the secondary planet hub and transmits the output torque and rpm of the
secondary reduction stage to the final planet reduction stage. The final planet hub is splined onto the cable drum.
In forward rotation, or when a load is raised, an over-running clutch, which connects the motor drive shaft to the
automatic brake assembly, permits free rotation of the sungear, without effecting the brake. When the winch rotation
is stopped, the load on the cable drum causes the over-running clutch to lock and the maximum load is held safely
by the disc brake.
FUNCTION IN REVERSE ROTATION (LOWERING):
In reverse rotation, or when the winch is pressurized for lowering of a load, hydraulic pressure from the reverse side
of the hydraulic motor is channelled to the brake piston, causing the brake piston to release the multi-disc brake
against a number of brake springs. The pressure required to release the brake is 400-800 psi (28-55 bar). The over-
running clutch, connecting the motor drive shaft to the brake assembly, locks, causing the brake disks to rotate
between divider plages, which are engaged into the brake housing. If the load on the cable drum tends to affect the
lowering speed, the resulting pressure drop in the brake piston causes friction between the brake discs and the
divider plates. In this way a completely smooth lowering speed can be achieved in a stepless operation by
modulation of the winch control handle. When the control handle is returned to neutral position, rotation stops and
the disc brake applies automatically.
During the lowering operation of the winch, the friction created by the brake discs results in heat. This heat is
dissipated by the circulation of hydraulic fluid through the brake housing, supplied externally. For efficient cooling
of the automatic brake, models with external circulation should be adjusted to supply 7.0 (US) gpm-26 l/min. This
circulation flow must be returned directly to the reservoir with a permissible back pressure of 30 psi (2 bar).
IMPORTANT: Under no circumstances must the pressure in the brake housing be permitted to exceed 30
psi (2 bar). Excessive pressure in the brake housing will damage the oil seal separating the
brake housing from the drum interior. Damage to this seal will cause the drum to fill up with
hydraulic fluid. In order to prevent potential damage to the drum seals and the end cover of
the winch, when the cable drum fills up with hydraulic fluid, a breather relief (see PARTS
REFERENCE, item 130) is installed on the end cover. The breather relief bleeds to atmosphere
and serves as a warning signal that the oil seal between brake housing and drum has been
damaged.
DESCRIPTION OF THE MODEL M75
354 REV.030819
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