Operation; Two-Position Controls; Control Options; Pressure Compensator Override (Pcor) Option - Danfoss 51 Series Service Manual

Service Manual

Operation

Two-position Controls

Control Options

8
Series 51 Two Position Controls Service Manual
Two-position controls shift the motor to either maximum or minimum displacement. Control input may
be hydraulic or electric. To change displacement, the control routes pilot pressure to one end of the servo
piston while draining the other.
A 4-way valve integral to the motor's endcap routes the flow of oil in all two-position controls except N2,
G1, G2 and PC. The 4-way valve consists of a spool and a logic sleeve. The control shifts the spool and
ports pressure to one end of the servo and drains the other. Ports in the logic sleeve regulate the flow
from the valve to the servo piston ends. The sleeve logic may be standard or reversed. The standard logic
sleeve defaults the motor displacement to maximum and shifts to minimum displacement when the
control operates. The reverse logic sleeve defaults the motor displacement to minimum and shifts to
maximum displacement when the control operates.
With N2 controls, external valving pressurized and drains the servo piston ends. With G1, G2 controls, a
two-position 4-way solenoid cartridge valve replaces the 4-way valve. The PC control feeds servo supply
pressure directly to the minimum displacement end of the servo piston.
Optional orifices in the control and motor end cap modulate shift speed.
Series 51 servo mechanism
4-way
valve
Servo piston

Pressure Compensator Override (PCOR) Option

The PCOR function allows the motor to match its displacement to the system load. The PCOR overrides
the control command allowing the motor to increase displacement when system pressure reaches a set
level due to load. This permits the motor to regulate system pressure by modulating the displacement of
the rotating group. As displacement increases, so does available torque while output speed decreases
and system pressure remains nearly constant at the PCOR setting.
11009442 • Rev CA • January 2015
Tamper resistant
cap
Minimum
displacement
limiter
Valve segment
Spacer
Miximum
displacement
limiter
P101 195E