With the propel lever (on operators console) in the NEUTRAL
position, the control valves are in the NEUTRAL position. The
spring-loaded servo-pistons hold the swashplates in the
center/neutral positions when the parking brake is ON.
Although the rotating groups are turned by the pump drive, no
high-pressure oil output is generated. With no pressure to
either side of the swashplate there is no oil flow from the
With the parking brake button pushed in (applied), the parking
brake valve is not energized. The springs in the brake apply
the parking brake.
Charge oil opens the charge relief valve, flows through the
pump case, and exits the pump through the case drain outlet.