NPSN (Pressure Compensated C Load Sensing Control)
D1P 130/145/193/260+NPSN
Pressure Compensated Control (P) Principle and Operation
Please refer to
NPNN (Pressure Compensated Control)
Load Sensing Control (S) Principle
The S control design matches pump flow with system demand. The S control senses the flow demand of
the system as a pressure drop across the external control valve (1).
As (1) opens and closes, the pressure difference (delta) across the valve changes. When opening, the delta
decreases. When closing, the delta increases. The S control then increases or decreases pump flow to the
system until the pressure delta becomes equal to the S setting as defined by the S adjusting screw and
spring.
Load Sensing Control (S) Operation
Through internal porting, system pressure [upstream of (1)] is applied to the non-spring end of the S
spool, and through hydraulic line connected at port X, load pressure [downstream of (1)] is applied to the
spring end. This arrangement allows the S spool to act on the delta between system pressure and load
pressure. The S spring sets the threshold of operation (S 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 (1) is
great enough to overcome spring force and shift the S spool porting system pressure to the servo piston.
The pump de-strokes reducing flow until the delta across the (1) becomes equal to the S setting.
When flow being delivered is less than demand, the delta across the (1) drops below the S setting and the
S spring shifts the spool connecting the servo piston to pump case. The pump strokes increasing flow
until the delta across the (1) becomes equal to the S setting.
When the external control valve (1) 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 low pressure standby mode.
(1) is not in the scope of supply.
Service Manual
D1 High Power Open Circuit Pumps Size 65/130/145/193/260
Operation
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Danfoss | July 2019
L1527453 | AX00000292en-CN0201 | 11