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Service Manual
Series T90 Axial Piston Pumps
Operation
T90 MDC solenoid override valve operation
Neutral start switch (NSS) for MDC
T90 HDC operation
T90 3-Position (FNR) electric control operation
High Current Electrical Displacement Control (HCEDC)
©
Danfoss | March 2020
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.
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.
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.
This control utilizes a 12 or 24 Vdc electrically operated spool valve to port pressure to either side of the
pump servo piston. Energizing one of the solenoids causes the pump to go to its maximum displacement
in the corresponding direction. All functions of the three-position (FNR) electric control are preset at the
factory
HCEDC Principle
An HCEDC is a displacement (flow) control. Pump swashplate position is proportional to the input
command and therefore vehicle or load speed (excluding influence of efficiency), is dependent only on
the prime mover speed or motor displacement.
P003 191
The High Current Electrical Displacement Control (HCEDC) consists of a pair of proportional solenoids on
each side of a three-position, four-way porting spool. The proportional solenoid applies a force input to
the spool, which ports hydraulic pressure to either side of a double acting servo piston. Differential
pressure across the servo piston rotates the swashplate, changing the pump's displacement from full
AX216086485386en-000101 | 15
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