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| Illustration 1 | g03206358 |
Hydraulic schematic of one travel motor group (1) Counterbalance valve group (2) Crossover relief valve group (3) Displacement change valve section (4) Travel motor section (5) Park brake | |
Note: Counterbalance valve group (1) consists of the counterbalance valve, four check valves and an orifice.
Counterbalance valve group (1) is mounted on the end of the head of the travel motor. The counterbalance valve directs flow from the travel control valve to the travel motor.
The counterbalance valve helps machine braking. The counterbalance valve helps to prevent an overspeed condition when the machine is driven downhill.
Check valves prevent the flow of the oil from going back to the travel control valves without first going through the travel motor and the counterbalance valve.
When the travel control valve is activated in the FORWARD position, flow enters the left side of the counterbalance valve. The makeup valve on the left side closes and flow the check valve opens. The pressure also goes through internal passages to the left end of the counterbalance spool. The counterbalance spool shifts to the right. The flow from the travel control valve goes through the flow check valve and the line to the travel motor. The return oil from the travel motor enters the spring chamber of the flow check valve on the right side. The oil flows through the throttling slots around the counterbalance spool to the center passage between the two flow check valves. The flow check valve opens and flow returns to the travel control valves through the line and to the tank.
If the machine is operated in reverse, the flow from the travel control valve enters the right side of the counterbalance valve. The flow through the counterbalance valve is the reverse of the flow in the forward direction.