Moog 761 Series Installation And Operation Instruction

1.INTRODUCTION
This manual provides instructions and procedures necessary to install, operate
and troubleshoot the Moog 761 series industrial servo valve. Troubleshooting instruc-
tions are outlined so that only the specific component(s) suspected of failure may be
identified.
2. OPERATION
The Moog 761 series industrial servo valve consists of a polarized electrical torque
motor and two stages of hydraulic power amplification. The motor armature extends
into the air gaps of the magnetic flux circuit and is supported in this position by a
flexure tube member. The flexure tube acts as a seal between the electromagnetic and
hydraulic sections of the valve. The two motor coils surround the armature, one on each
side of the flexure tube.
The flapper of the first stage hydraulic amplifier is rigidly attached to the midpoint
of the armature. The flapper extends through the flexure tube and passes between
two nozzles, creating two variable orifices between the nozzle tips and the flapper. The
pressure controlled by the flapper and nozzle variable orifice is fed to the end areas of
the second stage spool.
The second stage is a conventional 4-way spool design in which output flow from
the valve, at a fixed valve pressure drop, is proportional to spool displacement from the
null position. A cantilever feedback spring is fixed to the flapper and engages a slot at
the center of the spool. Displacement of the spool deflects the feedback spring which
creates a force on the armature/flapper assembly.
Input signal induces a magnetic charge in the armature and causes a deflection of
the armature and flapper. This assembly pivots about the flexure tube and increases the
size of one nozzle orifice and decreases the size of the other.
This action creates a differential pressure from one end of the spool to the other
and results in spool displacement. The spool displacement transmits a force in the feed-
back wire which opposes the original input signal torque. Spool movement continues
until the feedback wire force equals the input signal force.
DISASSEMBLY, MAINTENANCE, OR REPAIR OTHER THAN IN ACCORDANCE WITH THE
INSTRUCTIONS HEREIN OR OTHER SPECIFIC WRITTEN DIRECTIONS FROM MOOG WILL
INVALIDATE MOOG'S OBLIGATIONS UNDER ITS WARRANTY AND YIELD THE INTRINSICALLY
SAFE PROTECTION PERMIT NULL AND VOID.
CAUTION
761 Series Installation and
Operation Instruction
Electrohydraulic Servo valve
ELECTROHYDRAULIC VALVE CUT-AWAY
Coil
Armature
Nozzle
Feedback Wire
Spool
Filter
P A
Figure 1
Upper Polepiece
Flexure Tube
Lower Polepiece
Flapper
Inlet Orifice
T B P
X