Danfoss Series 45 Service Manual page 13

Service Manual
Series 45 Frame K and L Open Circuit Axial Piston Pumps
Features
© Danfoss | August 2016
Typical load-sensing control valve:Pressure drop across external control valve defines system demand
Load Return
pressure pressure
Tank
Load sense System
pressure pressure
Cross-section LS control: LS spool shifts to port system pressure to servo piston
System pressure
LS pressure
7 7 8 8 9 9
4 4 5 5 6 6
Case pressure
Servo pressure
The LS control consists of two spool valves that connect the servo piston either to pump case or system
pressure. The PC spool (6) controls the pressure-compensating function of the control as described in the
previous section. The LS spool (9) controls the load-sensing function. The PC spool has priority over the
LS spool.
Via internal porting, system pressure (upstream of ECV) is applied to the non-spring end of the LS spool
and via hydraulic line connected at port X, LS pressure (downstream of ECV) is applied to the spring end.
This arrangement allows the LS spool to act on the delta between system pressure and LS pressure. The
LS spring sets the threshold of operation (LS setting).
Because the swashplate is biased to maximum angle, the pump attempts to deliver full flow to the
hydraulic system. When the flow being delivered exceeds demand, the pressure delta across the ECV is
great enough to overcome spring force and shift the LS spool porting system pressure to the servo
piston. The pump de-strokes reducing flow until the delta across the ECV becomes equal to the LS
setting. When flow being delivered is less than demand, the delta across the ECV drops below the LS
setting and the LS spring shifts the spool connecting the servo piston to pump case. The pump strokes
increasing flow until the delta across the ECV becomes equal to the LS setting.
When the external control valve is placed in neutral, it connects the LS signal line to drain. With no LS
pressure acting on the non-spring end of the LS spool, the pump adjusts stroke to whatever position
necessary to maintain system pressure at the LS setting. The pump is now in standby mode.
Because of the series arrangement of the LS and PC spools, the PC spool will override the LS spool. If at
any time system pressure reaches the PC setting, the PC spool will shift blocking the passage that
connects the LS spool with the servo piston and porting system pressure to the servo piston causing the
pump to de-stroke.
P101 665E
P101 664E
520L0532 | AX00000040en-US0401 | 13