7Rev. C, April 2017
INTRODUCTION Moog D680 Series Proportional Control Valves
DESCRIPTION OF OPERATION
7
INTRODUCTION
Rev. C, April 2017
Moog D680 Series Proportional Control Valves
DESCRIPTION OF OPERATION
X YT A P B
T
V
B
V
P
V
A
V
Applications with Safety Requirements (Fail-safe)
When using this product in machines subject to safety
regulations, fail-safe versions can ensure that the spool is
moved to a defined safe position in the event of a failure.
Depending on the application, this safe position can be the
center position (for overlapped spools) or one of the end
positions P → A or P → B.
Moog offers several fail-safe options for the D680 Series
Proportional Control Valves to suit the needs of different
applications.
a) Biased pilot valves and springs to move the main stage
spool to an end position (fail-safe functions D and F):
The spring centered position of the D633 pilot valve is
either P → A or P → B. Thus, when the electrical power
fails and the hydraulic supply is still available, the pilot
valve will hydraulically move the main stage spool to its
end position P → A or P → B.
In addition, the main stage spool is also equipped with
mechanical springs. Thus, if the electric and hydraulic
supplies fail, the main stage spool is moved to its end
position P → A or P → B by spring force.
b) 4/2-way solenoid valve to override the pilot valve (fail-
safe functions U and W):
A solenoid valve is used to uncouple the pilot valve
from the main stage. When the solenoid valve is
de-energized, the hydraulic pilot supply is cut off from
the main stage and the springs will move the main
stage to its defined position. The main spool position
is now independent from the command signal and
the state of the pilot valve or the integrated valve
electronics. Depending on the application, several
options for the defined spool position are available:
Center position, slightly opened or fully opened to one
direction (P → A or P → B).
These versions of Moog Proportional Control Valves are
equipped with an additional logic output at the 11-pole +
PE connector to monitor if the valve is in the safe position.
For details refer to the section “Background - Electronics
Logic Functions“.
X YT A P B
T
V
B
V
P
V
A
V
D683/D684 valve with spring to move the main stage to an end
position
D683/D684 valve with integrated 4/2-way solenoid valve for
applications with safety requirements
Please note:
• If the movement of an actuator is blocked in the center
position, the main spool has to be equipped with a
sufficient overlap (>= ±10 %).
• All valves that include a 4/2-way solenoid are equipped
with 11-pole + PE connectors.
• Although the solenoid valve is wired via the 11-pole +
PE connector, it has to be operated independently and
is not connected to the integrated valve electronics.
• To reduce the fail-safe switching time to the center
position, it is advised to both switch off the supply of
the 4/2-way valve and the enable signal at the same
time. This does not apply if the defined position is the
fully opened position.
• For certain safety requirements, it might be necessary
to additionally monitor the position of the 4/2-way
solenoid valve. For these applications, monitored
versions of the 4/2-way solenoid valves are available
upon request.
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