Danfoss Series 45 Service Manual page 12

Service Manual
Series 45 Frame K and L Open Circuit Axial Piston Pumps
Features
12 | © Danfoss | August 2016
Cross-section pump: Bias spring and servo piston set swashplate position
PC control
The PC control is designed to maintain a constant pressure in the hydraulic circuit as flow varies. The PC
control modulates pump flow accordingly to maintain system pressure at the PC setting as defined by
the PC adjustment screw (4) and spring (5).
When system pressure, acting on the non-spring end of the PC spool (6), overcomes the force of the PC
spring, the spool shifts porting system pressure to the servo piston and the swashplate angle decreases.
When system pressure drops below the PC setting, the PC spring shifts the spool in the opposite
direction connecting the servo piston to pump case and the swashplate angle increases. The swashplate
is maintained at whatever angle is required to keep system pressure at the PC setting.
Cross-section PC control: PC spool shifts to port system pressure to servo piston
System pressure
Case pressure
4 4 5 5 6 6
Servo pressure
LS control
The LS control is designed to match pump flow with system demand. The flow demand of the system is
sensed by the LS control as a pressure drop across the External Control Valve (ECV). As the ECV opens and
closes, the pressure delta across the valve changes. When opening, the delta decreases. When closing,
the delta increases. The LS control then increases or decreases pump flow to the system until the
pressure delta becomes equal to the LS setting as defined by the LS adjustment screw (7) and spring (8).
P101 662E
520L0532 | AX00000040en-US0401