- The travel counterbalance valve prevents a shock load when travel is brought to an abrupt stop.
- The travel counterbalance valve prevents overspeed while the machine is travelling down a slope.
- The travel counterbalance valve prevents cavitation.
For more information about the operation of the travel motor, refer to Systems Operation, "Travel Motor".
Travel counterbalance valve (TRAVEL)
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| Illustration 1 | g01180635 |
Travel counterbalance valve (Travel) (1) Spring (2) Orifice (3) Port (4) Port (5) Orifice (6) Spring (7) Spring (8) Check valve (9) Plunger (10) Port (11) Port (12) Counterbalance valve (13) Check valve (14) Spring | |
Oil from the pump enters port (3) of the counterbalance valve through the control valve. The oil flows through check valve (8) to port (10) of the travel motor. The travel motor attempts to rotate. However, return oil from the travel motor flows from port (11) to the counterbalance valve. The pressure of the oil that is entering the motor increases, because the return oil is blocked by check valve (13) .
Oil pressure increases in port (3). The pressure acts on the end face of plunger (9) through orifice (2). The oil attempts to shift the plunger to the right. The force that is required to shift the plunger is proportional to the force that is created by spring (6) .
When the pressure in port (3) reaches approximately 1034 kPa (150 psi), plunger (9) begins to move to the right. The oil in port (11) goes back to the hydraulic tank. As the oil pressure in the pump increases, the rate of opening in the plunger also increases. As a result, the back pressure in port (3) becomes small. The rate of opening is automatically adjusted and the travel motor rotates at a speed that corresponds to the pressure of the oil and the flow of the oil in port (3). At approximately 1034 kPa (150 psi), the spool is fully shifted to the right.
Travel counterbalance valve (NEUTRAL)
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| Illustration 2 | g01180836 |
Travel counterbalance valve (Neutral) (1) Spring (2) Orifice (3) Port (4) Port (5) Orifice (6) Spring (7) Spring (8) Check valve (9) Plunger (10) Port (11) Port (12) Counterbalance valve (13) Check valve (14) Spring | |
When the operator moves the control lever to the NEUTRAL position, pump oil is blocked and spring (6) attempts to return plunger (9) to the neutral position. This is due to equal pressures in port (3) and port (4). When plunger (9) is shifted, the rate of opening in plunger (9) decreases. However, the travel motor is attempting to rotate because of the inertia of the machine. Therefore, the pressure in port (11) increases. As a result, the speed of plunger (9) is reduced, because the oil in the pilot pressure chamber passes through orifice (2). With this movement, the speed of the plunger is controlled and the shock load is absorbed. Also, the movement stops the travel motor without creating cavitation.