Patent ID: 7571558

Claim:
A backhoe hydraulic system comprising: a first pump and a second pump that supply pressurized oil to travel apparatus control valves and ground work apparatus control valves; a third pump that supplies pressurized oil to a swiveling base control valve; a fourth pump that supplies a pilot pressure; a travel detection circuit that is in communication with a discharge oil path of the fourth pump via a pressurized oil introduction orifice, and detects that the travel apparatus control valves have been operated; a first channel switching valve that is switchable between a merging position where pressurized oil from the first pump and the second pump merges together and is supplied to the ground work apparatus control valves, and an independent supply position where pressurized oil from the first pump and the second pump is respectively independently supplied to left and right travel apparatus control valves, wherein the first channel switching valve is switched to the merging position during a state of non-travel, and is switched to the independent supply position with pilot pressure when pressure has been established in the travel detection circuit by operation of the travel apparatus control valves; a second channel switching valve that is switchable between a non-supply position where pressurized oil from the third pump is not supplied to the ground work apparatus control valves, and a supply position where pressurized oil from the third pump is supplied to the ground work apparatus control valves, wherein the second channel switching valve is switched to the non-supply position during a state of non-travel, and is switched to the supply position with pilot pressure when pressure has been established in the travel detection circuit by operation of the travel apparatus control valves in a state in which the ground work apparatus control valves are being operated; and a pilot pressure control valve that is switchable between an operation position where pilot pressure is supplied to the first channel switching valve, and a non-operation position where pilot pressure is not supplied to the first channel switching valve, wherein the pilot pressure control valve is switched to the non-operation position during a state of non-travel, and is switched to the operation position with pilot pressure established in the travel detection circuit, and furthermore, in the operation position the pilot pressure control valve supplies pilot pressure to the first channel switching valve from the fourth pump on the upstream side of the pressurized oil introduction orifice.