overrides the control by reducing the pressure to the displacement control. As the control pressure
reduces, the internal forces rotating the swashplate overcome the force of the servo pistons and
decreases the pump’s displacement.
POR-Valve (180 frame size only)
Shuttle
valve
Multi-function valve
Multi-function valve
Bypass
adjustment
Charge pressure
relief valve
Pressure
override control valve
To control
Port "A"
Port "B"
P104 124E
Manual displacement control (MDC)
The manual displacement control converts a mechanical input signal to a hydraulic signal using a spring-
centered four-way servo valve. This valve ports hydraulic pressure to either side of a dual-acting servo
piston. The servo piston rotates the cradle swashplate through an angular rotation of ±17°, varying the
pump’s displacement from full in one direction to full in the opposite direction.The angular position of
the pump swashplate is proportional to the rotation of the control input shaft.
Non-Linear MDC
The non-linear manual displacement control operates in the same manner except that it is designed so
the change in the angular position of the pump swashplate progressively increases as the control input
shaft is rotated toward its maximum displacement position.
Solenoid override valve for MDC
A solenoid override valve option is available for the MDC. This safety feature returns the swashplate to
zero displacement. It is available in normally open (activate to allow) or normally closed (activate to
disallow) options..
Neutral start switch (NSS)
The neutral start switch is an optional feature available with the MDC. When connected properly with the
vehicle’s electrical system, the neutral start switch ensures that the prime mover can start only when the
control is in neutral position.
Hydraulic displacement control (HDC)
The hydraulic displacement control uses a hydraulic input signal to operate a spring-centered four-way
servo valve. This valve ports hydraulic pressure to either side of a dual-acting servo piston. The servo
piston rotates the cradle swashplate through an angular rotation of ±17°, thus varying the pump’s
displacement from full displacement in one direction to full displacement in the opposite direction. The
angular position of the pump swashplate is proportional to input pressure.
Service Manual
Series 90 Pumps
Operation
14
520L0818 • Rev 0101 • August 2015