Hydraulic circuitry for a backhoe

Claim 1

A hydraulic circuitry for a backhoe or the like comprising a multiplex valve assembly provided with a first center bypass including at least one first and second control valve connected to a hydraulic cylinder for swinging a boom about a horizontal axis and to a hydraulic motor for driving one of two travelling members, the first and the second control valve being connected in parallel to each other to a first pump, and a second center bypass including at least one third to fifth control valve successively connected to a further hydraulic motor for driving another travelling member, a hydraulic motor for slewing a platform as well as a hydraulic cylinder for flexing and stretching a shovel arm, the third to a fifth control valve being connected in parallel to each other to a second pump and the fourth control valve being downstream of the third control valve and upstream of the fifth control valve; wherein (a) the first control valve (V 1 ) is disposed upstream of the second control valve (V 2 ) relative to the first center bypass; (b) a sixth control valve (V 6 ) for a hydraulic cylinder (14) for swinging a bucket (11) and a seventh control valve (V 7 ) for a hydraulic cylinder (15) for actuating a dozer (7) are additionally disposed within the second bypass (A 2 ); (c) the sixth control valve (V 6 ), downstream of the fifth control valve (V 5 ) and upstream of the seventh control valve (V 7 ), is connected to these ones in parallel and to the second pump (P 2 ); (d) a first block (B 1 ) is interposed between the first (V 1 ) and the second control valve (V 2 ); (e) a second block (B 2 ) provided between the fourth (V 4 ) and the fifth control valve (V 5 ); (f) a first confluence line (D 1 ) provided to connect a first center bypass portion (a1) included in the first block (B 1 ) to a parallel connection line portion (e) included in the second block (B 2 ), said first confluence line (D 1 ) being adapted to pass a portion of fluid from the first pump (P 1 ) therethrough into the second center bypass when the hydraulic motor of the first center bypass is brought into operation and also when the work elements of the first center bypass are all idle, first confluence lines (D 1 ) connecting to a connection line (e) so that a plurality of control valves in the second bypass receive a portion of fluid from the first pump (P 1 ); (g) a second confluence line (D 2 ) provided to connect a downstream end of the first center bypass (a 1 ) to a second center bypass portion (a2) included in the second block (B 2 ) and to the parallel connection line portion (e) said second confluence line (D 2 ) being adapted to pass the remaining portion of fluid from the first pump (P 1 ) therethrough into the second center bypass when the work elements of the first center bypass are all idle; (h) a check valve (17) mounted on the first confluence line (D 1 ) to prevent backflow of the first center bypass portion (a1); (i) a further check valve (18) mounted on the second confluence line (D 2 ) between the second center bypass portion (a2) and the parallel connection line portion (e) in the second block (B 2 ) to prevent backflow to the second center bypass portion (a2); (j) a third check valve (19) mounted on a parallel connection line portion (e or e1) connected to the fourth control valve (V 4 ) to prevent backflow therein; and (k) a fourth check valve (21) mounted in the second bypass (A 2 ) between the fourth (V 4 ) and fifth control valve (V 5 ) to prevent backflow to the fourth control valve (V 4 ).