Dover TWG 250PR Service & Repair Manual - Page 3

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Dover TWG 250PR Service & Repair Manual

INTRODUCTION AND THEORY OF OPERATION

The TWG 250PR planetary gearbox is a hydraulically driven 2-stage planetary gearbox designed to
use a motor with SAE "A" 2-BOLT mount and 1.00" 6B spline shaft. This gearbox has a total ratio of
38:1.
The gearbox is designed to utilize a hydraulic motor, driving through a multiple-disc static oil brake,
into a pair of planetary gear sets to the output pinion.
The multiple-disc oil bath static park brake is spring applied and hydraulically released through a
port in the brake housing. The multiple-disc "service brake" is hydraulically applied through a port
in the brake housing.
During operation, dual counterbalance valves are used for dynamic braking to prevent the gearbox
from moving faster than desired. These counterbalance/brake valves partially block the main line
from the motor back to the directional control valve, allowing only a limited amount of hydraulic
fluid through the motor. The counterbalance valves are generally internally modulated by sensing
pressure on the supply line. Additionally, any time there is sufficient pressure to modulate the
counterbalance valves; this same pressure releases the static friction/stator style park brake.
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