| 摘要 |
An arrangement for adjusting the compressive force of drive rolls used for advancing a tree along a feed line for lopping. Drive rolls are arranged on opposite sides of the tree trunk and driven by hydraulic motors. Each drive wheel is pivotably mounted on its own arm and a cylinder-piston is connected between the arms and is used to adjust the distance between the drive rolls and to produce a compression force between them. A hydraulic circuit is provided which includes a drive motor, a pressure reducing valve and the cylinder-piston. The tank connection of the control pressure of the pressure-reduction valve is connected to the working pressure of the hydraulic motor so that when the rolls require a low rotating force the compression pressure created by the cylinder-piston is low and when the rolls require a high rotating force the working pressure required by the hydraulic motor increases and this working pressure increases the compression forces exerted by the cylinder-piston.
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