Pc, Pd; Operation; Functional Description; Pc Control - Danfoss 51 Series Service Manual

Service Manual

PC, PD

Operation

42
Series 51 Two Position Controls Service Manual

Functional Description

PC Control

The PC control consists of a multifunction block with PCOR valve attached. The multifunction block
contains the servo supply spool. It resolves high loop pressure for servo supply, and routes the high loop
pressure to the PCOR valve. At the same time it connects the low loop pressure to the PCOR.
The PC control uses a ported plug in place of the 4-way valve that connects the servo supply pressure to
the minimum displacement end of the servo piston. It drains the maximum displacement end to case
through orifice T7.
System pressure operates the PCOR valve. When system pressure reaches the PC threshold pressure, the
PCOR spool shifts, routing system pressure to the maximum displacement end of the servo piston,
saturating the T7 orifice, while draining the minimum displacement end to low loop. Optional orifices at
locations T1, T2, T3, T5, T7, U6 and U7 control shift speed. Brake pressure defeat option is not available
with the PC control.

PD Control

The PD control consists of a multifunction block with PCOR valve attached. The multifunction block
contains the servo supply spool that resolves high loop pressure, routing it to the 4-way valve for servo
supply, and to the PCOR valve.
The motor defaults to minimum displacement, shifting to maximum when directed by an external
hydraulic signal applied to port X1. This signal acts on the 4-way valve. When the signal pressure
overcomes the threshold spring force, the valve shifts.
External pressure in the range of 5 to 12 bar [72.5 to 174 psi] is required at port X1 to shift the motor to
maximum displacement. The threshold setting is adjustable within this range.
Pressure from an external source, applied to port X4 operates the PCOR valve. When this external
pressure reaches the PCOR setting, the PCOR spool shifts. This routes high system pressure to the
maximum displacement end of the servo piston while the minimum displacement end drains through
the 4-way valve out of X1.
Port X4 requires external pressure in the range of 130 to 370 bar [1890 to 5370 psi] to operate the PCOR
valve and shift the motor to maximum displacement. The PCOR threshold pressure setting is adjustable
within this range. Optional orificesT1, T2, T3, T7, T8, and U7 control shift speed. The PD control does not
have brake pressure defeat option.

Adjustment

PC, PD PCOR Adjuster Stop-pin

A stop-pin is installed in the PCOR adjuster to prevent over-travel of the PCOR valve spool. If the spool is
allowed to over-travel, due to high system pressure, it will close off flow to the servo piston. This would
keep the PCOR from shifting the motor toward maximum displacement and regulating the system
pressure.
The stop-pin must protrude from the spring seat (dimension X, shown) 24 mm [0.94 inch] for PCOR
settings of 110 to 260 bar [1600 to 3750 psi] or 19 mm [0.74 inch] for PCOR settings of 270 to 370 bar
[3900 to 5370 psi].
11009442 • Rev CA • January 2015