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DESCRIPTION OF THE MODEL PL8
GENERAL DESCRIPTION:
The PULLMASTER Model PL8 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
✛ Over-running clutch
✛ 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 of the primary reduction stage is 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 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 paying out 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. A hydraulic counterbalance valve or holding valve is not required for smooth and positive operation
of the automatic brake.
During the lowering operation of the winch, the friction created by the brake discs results in temperature. This
temperature is dissipated by an internal circulation flow, supplied out of the hydraulic motor or from an external
source. For models with external circulation, supply winch with approximately 2.5 (US) gpm - 9.5 l/min circulation
flow. 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.
271 REV.970407
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