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GENERAL DESCRIPTION:
The PULLMASTER Model M25 is a planetary hydraulic winch having equal speed in both directions. The main
components of this unit are:
✛ Hydraulic gear motor
✛ Multi disc brake with static and dynamic function
✛ Primary planet reduction
✛ Final planet reduction
✛ Brake housing
✛ Cable drum
✛ Final drive housing
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 final reduction stage by the final sungear, which is splined to the primary planet hub.
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 over-running clutch, connecting the motor drive shaft to the brake
assembly, locks, causing the brake discs to rotate between divider plates which are engaged into the brake
housing. If the load on the cable drum tends to effect 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 lowering operations of the winch, the friction created by the brake discs results in temperature. This
temperature is dissipated by the circulation of hydraulic fluid through the brake housing, supplied internally from
the motor or externally depending on the brake code of the winch. For efficient cooling of the automatic brake,
models with external circulation should be adjusted to supply 5 (US) gpm (19 l/min). This 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 damage to the drum seal and end cover of the final drive housing, 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
that the seal between brake housing and drum has been damaged.
249 REV.040708
DESCRIPTION OF THE MODEL M25
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