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| Illustration 1 | g00604794 |
(1) Pilot logic network. (2) Bucket valve. (3) Return passage for the pilot logic network. (4) Valve for the left piston motor (travel). (5) Parallel passage. (6) Straight travel valve. (7) Valve for the right piston motor (travel). (8) Piston pumps. | |
The combined function hydraulic system allows the operator to use one of the hydraulic functions while the machine continues to travel in a straight line.
The straight travel valve (6) is supplied by the piston pumps (8). When the travel valves (4) and (7) are moved, pressure in the pilot logic network (1) increases. The pressure causes the straight travel valve to shift to the working position. This routes oil to the piston motors (travel) only.
If the travel levers are moved and another hydraulic function is used, pressure in the pilot logic network increases. The increased pressure shifts the straight travel valve to the lower position. The flow from the piston pumps is split between the travel valves and the hydraulic function. The following example describes the operation of the system when the bucket function is used and the machine is travelling.
When the travel levers are moved forward, the spools in the travel valves shift upward. The pressure in the pilot logic network increases in order to shift the spool in the straight travel valve to the middle position. This is done because the return passage (3) for the pilot logic network is restricted. When the bucket is closed, the spool in the bucket valve (2) shifts downward. This causes the flow in the pilot logic network to be totally restricted from going to the return passage. The pressure in the pilot logic network increases. This causes the spool in the straight travel valve to shift to the lower position. The flow from the piston pumps then flows to the travel valves and to the bucket valve through the parallel passage (5).