Patent ID: 7743611

Claim:
A backhoe hydraulic system comprising: travel pumps (P 1 , P 2 ) for feeding pressure oil to control valves (V 4 , V 5 ) for a travel device; a swivel pump (P 3 ) for feeding pressure oil to a control valve (V 1 ) for a swivel base; a first flow channel switching valve (V 12 ) that is capable of switching between a work position ( 31 ) in which the pressure oil from said travel pumps is fed to control valves (V 6 , V 7 , V 8 ) for a ground working device during non-travel, and a travel position ( 34 ) in which the pressure oil from said travel pumps is fed to control valves (V 4 , V 5 ) for a left-right travel device during travel; a second flow channel switching valve (V 13 ) that is capable of switching between a non-feed position ( 39 ) in which the pressure oil from said swivel pump (P 3 ) is not supplied to the control valves (V 6 , V 7 , V 8 ) for said ground working device, and a feeding position ( 40 ) in which the pressure oil from said swivel pump (P 3 ) is fed to the control valves (V 6 , V 7 , V 8 ) for the ground working device; a travel detection circuit ( 54 ) for feeding a pilot pressure to the first flow channel switching valve (V 12 ) to switch the first flow channel switching valve (V 12 ) to said travel position ( 34 ) when the control valves (V 4 , V 5 ) for said travel device are operated; and a flow channel switching circuit ( 41 ) that is capable of feeding a pilot pressure to the second flow channel switching valve (V 13 ) so as to switch the second flow channel switching valve (V 13 ) to the feeding position ( 40 ) when the control valves (V 4 , V 5 ) for said travel device are operated during operation of the control valves (V 6 , V 7 , V 8 ) for said ground working device; wherein a flow channel switching operation valve (V 17 ) is provided to said flow channel switching circuit ( 41 ), and the flow channel switching operation valve (V 17 ) is configured so as to be capable of switching between a non-operating position ( 58 ) in which the pilot pressure is not fed to said second flow channel switching valve (V 13 ), and an operating position ( 59 ) in which the pilot pressure is fed to said second flow channel switching valve (V 13 ), and so as to be switched to the operating position ( 59 ) by the pilot pressure from said travel detection circuit ( 54 ); and wherein said second flow channel switching valve (V 13 ) switches from the non-feeding position ( 39 ) to the feeding position ( 40 ) at the same time as said first flow channel switching valve (V 12 ) or before said first flow channel switching valve (V 12 ) when the control valves (V 4 , V 5 ) for said travel device are operated during operation of the control valves (V 6 , V 7 , V 8 ) for said ground working device, and said first flow channel switching valve (V 12 ) is switched from the work position ( 31 ) to the travel position ( 34 ).