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GENERAL DESCRIPTION:
The PULLMASTER Model M12 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
✛ 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. The pressure required to rotate the drum at full speed may vary
up to 250 psi (17 bar) without load. 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 pressure
required to rotate the drum at full speed may vary from 250 to 500 psi (17 to 34 bar) depending upon load and without
load from 500 to 800 psi (34 to 55 bar). The over-running clutch, connecting the motor drive shaft to the brake
assembly, locks, causing the brake discs to rotate between divider plates. Thus, a completely smooth lowering
speed can be achieved in a stepless operation by modulation of the winch control valve 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 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 the required flow is approximately 3.5 (US) gpm - 13 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.
245 REV.990710
DESCRIPTION OF THE MODEL M12
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