ME12002
HYDRAULIC SYSTEM
Section Drive Counterbalancing System (straight travel)
Straight travel spool (305) allows the machine to continue to be driven straight while performing other operations, for example, swinging the boom while driving. See Figure 3-150. If driving and not performing any other operations, hydraulic fluid from front pump (27) flows through straight travel spool (305), travel left spool (301L), and into the left travel motor. Hydraulic fluid from rear pump (28) flows through travel right spool (301R) and into the right travel motor. See Figure 3-150. Unless there are travel resistance differences between the two drive motors, the excavator continues to drive straight because the left and right drive circuits are isolated from each other. Performing Other Functions While Driving If operating the excavator using both valves: 1. When driving, only hydraulic fluid from rear pump (28) flows into both travel motors. See Figure 3-150.
Figure 3-149 Section Drive 1 2 3 PL PR
2. When driving and performing other functions, only hydraulic fluid from front pump (27) flows for all other functions. Flow required for all other functions while driving reduces because these functions operate at a reduced speed to maintain the safety and stability of the machine. See Figure 3-150.
Plug Main pressure limiting valve (MR) Spool Port pump 1 Port pump 2
Drive Counterbalancing System Function (straight travel)
Any remaining hydraulic fluid from front pump (27) flows into both travel motors. See Figure 3150. If the machine does not have the straight travel function, hydraulic fluid flow supplied into each drive motor from one pump differs from that of the other pump. Because of the difference between flow suppliled, the machine cannot travel straight.
Figure 3-150 Drive Function Printed in U.S.A
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909768/BP1207
