Oil makeup operation
(1) Motor rotary group
(2) Left travel motor
(4) Check valve
(9) Left travel control valve
(11) Return passage
In order to prevent cavitation in the travel motor during travel stop, makeup oil is supplied to the travel motor.
The following description is given for travel stop of the left travel motor. The right travel motor functions in the same manner as the left travel motor.
During travel stop, the travel levers/pedals are moved to the NEUTRAL position. The oil delivery from the left pump through passage (8) is blocked at travel control valve (9). The oil delivery from the left pump is not supplied to the left travel motor.
Since no oil delivery is supplied to left travel motor (2), the travel motor will attempt to stop. However, the travel motor will continue to rotate because of the inertia (weight and size) of the machine. This causes a vacuum condition in passage (3) of the travel motor.
When travel control valve (9) is in the NEUTRAL position, return oil flows from return passage (11) through passage (8). The return oil then flows through line (7), swivel (6), line (5), check valve (4) and passage (3) to motor rotary group (1) as makeup oil. This makeup oil prevents cavitation in the travel motor during travel stop.
Makeup oil is supplied for forward travel in the same manner as reverse travel.