Disengaged
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| Illustration 1 | g01180635 |
Counterbalance valve (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). This increased pressure acts on the end 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 system pressure in port (3) reaches approximately 1034 kPa (150 psi), valve (9) starts moving to the right. When the system pressure reaches 3447 kPa (500 psi), valve (9) is fully shifted to the right.
Engaged
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| Illustration 2 | g01180836 |
Parking brake (parking brake engaged) (1) Spring (2) Orifice (3) Port (4) Port (5) Orifice (6) Spring (7) Spring (8) Check valve (9) Plunger (10) Port (11) Port (12) Throttle for the plunger (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.