Patent ID: 7350353

Claim:
A hydraulic circuit including a first system having a changing valve for a right side running motor that is connected to a first pump and controls supply of a hydraulic oil to the right side running motor, and a changing valve for a first actuator of a closed center type that is connected to the first pump and controls supply of the hydraulic oil to the first actuator; and a second system having a changing valve for a left side running motor that is connected to a second pump and controls supply of a hydraulic oil to the left side running motor, and a changing valve for a second actuator of a closed center type that is connected to the second pump and controls supply of the hydraulic oil to the second actuator; comprising: the changing valve for the right side running motor and the changing valve for the left side running motor that are the changing valves of a center bypass type; the changing valve for the first actuator that is tandem-connected to the changing valve for the right side running motor; the changing valve for the second actuator that is tandem-connected to the changing valve for the left side running motor; a supply path for right side running for introducing the hydraulic oil from the first pump into the changing valve for the right side running motor; a supply path for the left side running for introducing the hydraulic oil from the second pump into the changing valve for the left side running motor; a first supply path for introducing the hydraulic oil from the downstream side of a center bypass path in the changing valve for the right side running motor into the changing valve for the first actuator; a second supply path for introducing the hydraulic oil from the downstream side of a center bypass path in the changing valve for the left side running motor into the changing valve for the second actuator; and a merging valve having a merging position that communicates the first supply path with the second supply path and interrupts the supply path for the right side running and the supply path for the left side running, a running direct position that communicates the first supply path with the second supply path and communicates the supply path for the right side running and the supply path for the left side running, and an interruption position that interrupts the first supply path and the second supply path and interrupts the supply path for the right side running and the supply path for the left side running.