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
P104 049
4
5
6
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 and spring.
Typical load-sensing control valve
Load
pressure
Load sense
pressure
System
pressure
Tank
Return
pressure
P101 665E
Pressure drop across external control valve defines system demand
Cross-section LS control
Spool
Spring
guide
Spring
LS adjusting
plug
LS spring
PC adjusting
plug
Plug
Plug
Spool
Spring
guide
Spring
(PC heavy)
P104 051
The LS control consists of two spool valves that connect the servo piston either to pump case or system
pressure. The PC spoolcontrols the pressure-compensating function of the control as described in the
previous section. The LS spool 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).
Service Manual
Series 45 Frame K2 Open Circuit Axial Piston Pumps
Features
12 |
©
Danfoss | April 2017
AX00000301en-US0101
