User Manual

000 293 646 0 - SYS-H XERION 3300 - 04/05 19
1 Overall hydraulic system
PFC pump
391
Description of function When a control unit is actuated, a load pressure builds up in the LS line. In this
process, the following conditions result at the volume flow controller (772):
– the pump pressure acts on the right face end
– the load pressure and the spring force of the compression spring (margin
pressure) (21) act in the spring space.
– Since the load pressure + the spring force of the compression spring
(margin pressure) (21) is higher than the pump pressure on the right face
end, the volume flow controller is moved to the right.
This :
– shuts off the passage of the pump pressure to the variable-displacement
pump hydraulic cylinder (377);
– connects the variable-displacement pump hydraulic cylinder (377) with the
tank (no pressure on top side of ram)
– makes the control spring (15) swing out the swash plate (17).
The pump now feeds a higher volume flow. This process is referred to as
"Upstroking". The volume flow of the pump is determined by the restrictor effect
of the open spool cross-section or by the setting of a control unit.
Lower volume flow requirement: When the spool cross-section is reduced (the volume flow is to be reduced), the
load pressure at the input (7) drops. This changes the force ratio at the volume
flow controller (772), actuating the volume flow controller to the left according to
the pressure drop, against the compression spring. The variable-displacement
pump hydraulic cylinder (377) is subject to pressure and the swash plate (17) is
set to a flatter position, and the pump performs a downstroke until the volume
flow requirement is met.
Higher volume flow require-
ment.
An example: A control unit has been actuated. The load pressure is 140 bar, the
pump pressure now goes to (160 bar).(Load pressure 140 bar + 20 bar margin
pressure). When another control unit with a load pressure of 100 bar is actuated
now, the pump pressure drops slightly.
This also decreases the pressure on the top face of the variable-displacement
pump hydraulic cylinder (377) accordingly, the swash plate (17) is moved to a
steeper position, increasing the volume flow until the additional volume flow
requirement of the second circuit has been met and the pump pressure of 160
bar has been re-established. The load pressure on the controller remains stable
at 140 bar.