Jet pipe
Annular
area
Nozzle
Receiver
2
Operating Principle of the Two-Stage Valve
An electric input signal (flow rate command) is applied to the integrated
control amplifier which drives a current through the coils of the pilot stage
torque motor. Thus the deflected nozzle-flapper system produces a pressure
difference across the drive areas of the spool and effects its movement. The
position transducer which is excited via an oscillator measures the position
of the spool (actual value, position voltage).
This signal is then rectified by a demodulator and is fed back to the control
amplifier where it is compared with the command signal. The control amplifier
drives the torque motor until command voltage and feedback voltage are equal.
Thus, the position of the spool is proportional to the electric command signal.
Proportional Flow Control Valve D661-...P
The nozzle flapper design of the pilot stage has been converted into an
improved version with jet pipe amplifier (ServoJet
®
).
The ServoJet
®
pilot stage consists mainly of torque motor, jet pipe and
receiver.
A current through the coil displaces the jet pipe from neutral. This
displacement combined with the special shape of the nozzle directs a focussed
fluid jet more into one receiver bore than into the other.
The jet now produces a pressure difference in the control ports. This
pressure difference results in a pilot flow, which in turn causes a spool
displacement. The pilot stage drain is through the annular area around the
nozzle to tank.
Operating Principle of the Two-Stage Valve
An electric input signal (flow rate command) is applied to the integrated
control amplifier which drives a current through the coil of the pilot stage
torque motor. The thus deflected jet pipe produces a pressure difference
across the drive areas of the spool and effects its movement.
The position transducer which is excited via an oscillator measures the
position of the spool (actual value, position voltage). This signal is then
demodulated and fed back to the controller where it is compared with the
command signal. The controller drives the torque motor until the error
between command signal and feedback signal is zero. Thus the position of the
spool is proportional to the electric command signal.
Failsafe Version D661-...P
For applications with proportional control valves where certain safety
regulations are applicable, a defined metering spool position is needed in order
to avoid potential damage.
Therefore, failsafe versions are offered as an
option for the MOOG proportional valves.
After external triggering, this failsafe function causes a defined metering
spool position.
Mechanical Failsafe version (biased pilot stage with mechanical feedback)
The safe position of the spool will be obtained after cut off of pilot
pressure supply (external pilot connection) or operating pressure supply
(internal pilot connection).
This safe position can only be obtained with <1 bar pilot pressure.
D661-P...A/BW
D661-P...A/BU
Proportional Valve
D661-P...A/BW
and D661-P...A/BU Series
with electrically operated
failsafe function
Proportional Valve
D661-P...AP Series
with electrically operated
failsafe function
2- stage Proportional Valve
D661-...P...A/B Series
Servovalve D661 - ...S and H
Series with additional
mechanical feedback
ATTENTION
