Patent ID: 7780102

Claim:
A wood chipper having a disintegrating member, and a feed roller operable at different speeds for feeding material to be disintegrated into said disintegrating member, a hydraulic motor for driving the feed roller, and a pump assembly for providing hydraulic fluid under pressure to the hydraulic motor, the hydraulic motor normally increasing the speed of the feed roller as hydraulic fluid pressure supplied to the hydraulic motor is increased, the pressure of the hydraulic fluid required to operate the hydraulic motor increasing as loading on the feed roller is increased, said pump assembly including at least a first pump stage providing a first output flow, and a second pump stage providing a second output flow, the output flows provided by the first and second pump stages being added to each other, and a bypass valve connected to the output of the second flow pump stage, and opening when fluid pressure provided to the hydraulic motor is at a selected level due to loading on the feed roller to divert the output flow of the second pump stage from the added flow so as to thereby reduce the speed of the feed roller.