Oil makeup operation
(1) Motor rotary group
(2) Left travel motor
(4) Check valve
(9) Left travel control valve
(11) Return line
Return oil flow from the travel control valve is used as makeup oil. Makeup oil prevents a vacuum condition in the travel motor when operation is stopped. The description for makeup operation is given for left travel. The makeup operation for left travel functions in the same manner as the makeup operation for right travel.
When left travel control valve (9) is returned to the NEUTRAL position in order to stop left travel, pump oil supply to left travel motor (2) is blocked at passage (10) . The motor continues to rotate because of the mass (weight and size) of the machine. Oil pressure decreases at passage (3) of motor rotary group (1) . Check valve (4) opens.
When left travel control valve (9) is in the NEUTRAL position, return oil from return line (11) flows to passage (8) . The return oil then flows through line (7) , through swivel (6) and through line (5) . The return oil then enters left travel motor (2) . The oil passes through check valve (4) and passage (3) . The oil then enters motor rotary group (1) as makeup oil. The makeup oil circuit eliminates the possibility of cavitation in the travel motor.