Abstract: A wood chipper or grinder includes counter rotating upper and lower feed drums driven by a hydraulic motor at variable fluid pressure to produce variable torque to the feed drums. Wood debris fed to a gap between the rollers is advanced toward a grinder or chipper to reduce the material. A hydraulic feed control system operates off the variable hydraulic pressure associated with the motor and, in an automatic mode, exerts more or less downward clamping pressure on the upper feed drum with changes in pressure to the motor. The system sets an upper limit on the clamping pressure in the automatic mode which can be overridden manually if necessary to apply greater downward force than that achievable in the automatic mode. The upper feed drum can also be manually raised if necessary.

Abstract: A wood chipper or grinder includes counter rotating upper and lower feed drums driven by a hydraulic motor at variable fluid pressure to produce variable torque to the feed drums. Wood debris fed to a gap between the rollers is advanced toward a grinder or chipper to reduce the material. A hydraulic feed control system operates off the variable hydraulic pressure associated with the motor and, in an automatic mode, exerts more or less downward clamping pressure on the upper feed drum with changes in pressure to the motor. The system sets an upper limit on the clamping pressure in the automatic mode which can be overridden manually if necessary to apply greater downward force than that achievable in the automatic mode. The upper feed drum can also be manually raised if necessary.