Pump Servo Valves
Servo Piston Assembly.
(1) Lever. (2) Piston. (3) Swashplate neutral adjusting screw.
(4) Cavity. (5) Cavity.
The pump swashplate is moved by the servo piston assembly.
The servo piston is a double-acting piston that is a part of the
propel pump. The swashplate is connected to the center of the
piton with lever (1).
The control valve is manual displacement controlled. The
valve controls the flow of charge oil to the servo piston
When the propel lever is in the NEUTRAL position, the control
valve is spring centered. Charge oil is blocked by the valve
spool and both ends of the servo piston assembly are vented
to the hydraulic oil tank. Piston (2) is held in the center
position by adjusting screw (3) and a spring. The pump
swashplate will remain at zero angle and there is no oil flow
from the pump.
When the propel lever is in the FORWARD or REVERSE
position, the control valve is shifted. The oil shifts the servo to
put the pump on stroke. The manual displacement control
spool has a return spring located externally of the pump.