100-P-0000047-E-10/04.2020
L.8S directional valves
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2-way compensator that must be positioned between the
pump port and the pressure gallery inside the block.
When all directional valves are in the neutral position, the
2-way compensator closes the inlet to the valve block.
When one of the directional valves is operated, the 2-way
compensator reduces the inlet pressure to a level sufficient
to keep the pressure difference between the pressure and
control galleries inside the block at a constant level. This en
sures that the flow rate to the actuator is independent of the
load and proportional to the open flow area of the metering
orifice in the directional valve. The flow rate supplied to the
valve block therefore matches the actual demand.
When a valve block is supplied by a variable-displacement
pump with a load-sensing control. the pump can be connec
ted directly to the valve block by a pressure line. In addition,
the control line is connected to the pump control port. If the
control pressure can be adjusted directly at the pump con
trol, it is then possible to set the actuator flow rate to the spe
cified value without any additional measures.
If the pump control pressure is preset, the specified flow rate
is achieved by placing a 2-way compensator before the dir
ectional valve.
When all directional valves are in the neutral position, the
pump is de-stroked. When one of the directional valves is
operated then, due to the effect of either the pump control
or the 2-way compensator positioned before the directional
valve, the necessary control pressure is maintained
between the pressure and control galleries inside the block.
The flow to the selected actuator is therefore independent
of the load and proportional to the open flow area of the
metering orifice in the directional valve.
In all of the system configurations described up to this point,
when several directional valves are operated then, thanks
to the shuttle valves situated in the control lines, the actuator
with the highest load will dictate the control pressure and the
flow rate to the actuator will be independent of the load and
proportional to the open flow area of the metering orifice in
the directional valve. Load-independence for the less
highly-loaded actuators can be achieved by using individual
pressure compensators, which reduce the excessive pres
sure difference sufficiently to ensure that the required con
trol pressure exists at the corresponding directional valve.
2 The main components
2.1 Inlet- and end sections for valve
blocks
Every L.8S series valve block requires two block termina
tion components in the form of one inlet section and one end
section. These two components are used for mounting the
block, the block tie bolts pass through them, and they are
provided with hydraulic ports.
2.2 Inlet and intermediate sections
2.2.1 2-way pressure compensator
The 2-way compensator is a valve that controls a pressure
differential. It is situated inside the block, before the pressu
re gallery. In this valve, the inlet pressure is reduced by the
amount needed to ensure that the control pressure between
the pressure and control galleries inside the block is kept
constant. In some models, the valve closes the inlet to the
block if the pressure in the control line reaches the setting
of an upstream pressure relief valve.
The 2-way compensator can be supplied as an inlet section
or an intermediate section.
2.2.2 3-way pressure compensator
The 3-way compensator is a valve that controls a pressure
differential. It is situated between the pressure gallery and
the tank or carry-over gallery. The valve keeps the pressure
difference between the pressure and control galleries inside
the block at a constant level and surplus flow passes to the
tank or carry-over port. If the pressure in the control line
reaches the setting of an upstream pressure relief valve, the
3-way compensator opens the connection to tank, thus lim
iting the pressure in the pressure gallery inside the block. In
one particular model, the function of the 3-way compensator
can be customized to suit the requirements of individual ap
plications. The adjustment can be done with a shut-off
screw that is accessible from the outside.