Reverse, High Speed With Parking Brake Off
(1) Flushing valve. (2) Charge relief valve. (3) Line from charge filter. (4) Tandem propel pump. (5) Axle propel motor. (6) Servo control valves. (7)
Drum drive motor. (8) Brake interlock valve. (9) Unfiltered charge oil. (10) Parking brake and speed shift valve. (11) Thermal bypass valve. (12)
Hydraulic oil tank. (13) Line from charge filter relief. (14) Hydraulic oil cooler. (15) Axle motor flushing valve. (16) Drum motor flushing valve
When the parking brake button is pulled out (released), parking
brake and interlock valves (8) are energized. The parking
brake valve shifts to the right. Charge oil goes to the parking
brake and moves the piston against the spring force and
releases the parking brake. The interlock valve shift to the left
when energized. The passage for each side of the pump
control piston is now separated and the swashplate will move
when oil is directed to one side.
When the operator moves the propel lever to the REVERSE
position, servo control valves (6) shift from the neutral position.
Filtered charge oil enters the pump at line (3). Charge oil flows
through the control valves to the servo-pistons, causing the
swashplates to rotate.
Swashplate angle is determined by how far the propel lever is
moved off center. Due to normal operating force changes, the
swashplates tend to drift from the set position. Drift is sensed
by the feedback linkage connecting the swashplates to the
control valves. This activates the control valves, supplying
pressure to the servo-pistons and maintaining the swashplates
in the set position.