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DESCRIPTION OF THE MODEL H25
GENERAL DESCRIPTION:
The PULLMASTER Model H25 is a planetary, hydraulic winch with reversing or lowering speed 4.67 times faster
than forward or hoisting speed. 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
★ final drive housing
★ cable drum
FUNCTION IN FORWARD ROTATION (HOISTING):
In forward rotation, 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 shaft, 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 sun gear 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, hydraulic pressure from the reversing 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 with the internal gear of the primary planet reduction locks,
causing the internal gear to rotate at the same rpm as the primary sungear. Thus, the primary reduction stage
is eliminated and the output torque and rpm of the hydraulic motor are transmitted directly to the final planet
reduction stage. With the primary reduction stage eliminated, the reduction is reduced to a ratio of 8.75:1 and
the cable drum will rotate 4.67 times faster than in forward or hoisting speed.
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 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 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 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 back 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 the brake housing and drum has been
damaged.
251 REV.040708
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