Backhoe hydraulic system

A backhoe hydraulic system comprising:

• travel pumps (P1, P2) for feeding pressure oil to control valves (V4, V5) for a travel device;
• a swivel pump (P3) for feeding pressure oil to a control valve (V1) for a swivel base;
• a first flow channel switching valve (V12) that is capable of switching between a work position (31) in which the pressure oil from said travel pumps is fed to control valves (V6, V7, V8) 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 (V4, V5) for a left-right travel device during travel;
• a second flow channel switching valve (V13) that is capable of switching between a non-feed position (39) in which the pressure oil from said swivel pump (P3) is not supplied to the control valves (V6, V7, V8) for said ground working device, and a feeding position (40) in which the pressure oil from said swivel pump (P3) is fed to the control valves (V6, V7, V8) for the ground working device;
• a travel detection circuit (54) for feeding a pilot pressure to the first flow channel switching valve (V12) to switch the first flow channel switching valve (V12) to said travel position (34) when the control valves (V4, V5) 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 (V13) so as to switch the second flow channel switching valve (V13) to the feeding position (40) when the control valves (V4, V5) for said travel device are operated during operation of the control valves (V6, V7, V8) for said ground working device;
• wherein a flow channel switching operation valve (V17) is provided to said flow channel switching circuit (41), and the flow channel switching operation valve (V17) 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 (V13), and an operating position (59) in which the pilot pressure is fed to said second flow channel switching valve (V13), 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 (V13) switches from the non-feeding position (39) to the feeding position (40) at the same time as said first flow channel switching valve (V12) or before said first flow channel switching valve (V12) when the control valves (V4, V5) for said travel device are operated during operation of the control valves (V6, V7, V8) for said ground working device, and said first flow channel switching valve (V12) is switched from the work position (31) to the travel position (34).