Moog 761 Installation And Operation Instruction Manual

1. INTRODUCTION

This manual provides instructions and procedures necessary to install,
operate and troubleshoot the Moog G761/761 series industrial servovalve.
Troubleshooting instructions are outlined so that only the specific component(s)
suspected of failure may be identified.

2. OPERATION

The Moog G761/761 series industrial servovalve 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.

G761/761 Series Installation and

Operation Instruction

Electrohydraulic Servovalve

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 feedback wire which opposes the original input signal torque. Spool
movement continues until the feedback wire force equals the input signal force.

CAUTION

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.

ELECTROHYDRAULIC VALVE CUT-AWAY

Coil

Armature

Nozzle

Feedback Wire

Spool

Filter

P A T B P

Figure 1 Moog Series G761/761

Upper Polepiece

Flexure Tube

Lower Polepiece

Flapper

Inlet Orifice

x

Relocate screw
and seal washer to
P port for external
(5th port) pilot
oil supply

Location of
screw and seal
washer for
standard internal
(4th port) pilot
oil supply

3. HYDRAULIC SYSTEM PREPARATION

To prolong servovalve operational life and to reduce hydraulic system
maintenance, it is recommended that the hydraulic fluid be kept at a cleanliness
level of ISO DIS 4406 Code 16/13 maximum, 14/11 recommended. The most
effective filtration scheme incorporates the use of a kidney loop or “off-line”
filtration as one of the major filtration components. The filter for the “off-line”
filtration scheme should be a B3≥75 filter for maximum effectiveness.
Upon system startup and prior to mounting the servovalve, the entire
hydraulic system should be purged of built-in contaminating particles by an
adequate flushing. The servovalve should be replaced by a flushing manifold and
the hydraulic circuit powered up under conditions of fluid temperature and fluid
velocity, reasonably simulating normal operating conditions. New system filters are
installed during the flushing process whenever the pressure drop across the filter
element becomes excessive. The flushing processes should turn over the fluid in
the reservoir between fifty to one hundred times.
To maintain a clean hydraulic system, the filters must be replaced on
a periodic basis. It is best to monitor the pressure drop across the filter
assembly and replace the filter element when the pressure drop becomes
excessive. In addition to other filters that are installed in the hydraulic circuit,
it is recommended that a large capacity, low pressure ß3≥75 filter be installed
in the return line. This filter will increase the interval between filter element
replacement and greatly reduce the system contamination level.

4. PILOT STAGE OIL SUPPLY AND NAMEPLATE
MODIFICATION (applies to models G761-3001B through G761-3010B)

The Moog G761/761 series industrial servovalve can be configured for pilot
stage oil supply through the internal pressure “P” port, or from a separate supply
line through the “X” port. Standard configuration is internal pilot operation with
a screw and seal washer in the “X” port. This same screw and seal washer must
be relocated to the “P” port if an external pilot oil supply source is desired. Refer
to Figure 2 for screw and seal washer locations.

Upon valve installation, the nameplate must display the proper hydraulic
schematic and typecode (if applicable). The nameplate currently shows internal
(4th port) pilot hydraulic schematics and typecode. If a separate pilot supply will
be used, please attach the provided lower half label showing external (5th port)
information. See Figure 3.

5. INSTALLATION

The Moog G761/761 series industrial servovalve may be mounted in any
position, provided the servovalve pressure, control and return ports match their
respective manifold ports.
The mounting pattern and port locations of the servovalve are shown on
Figure 6. The servovalve should be mounted with 5/16-18 x 1.75 inch long, socket
head cap screws. Apply a light film of oil to the screw threads and torque to
96 inch pounds. Wire the mating connector for desired coil configuration and
polarity. Thread the connector to valve.

6. NULL ADJUSTMENT

It is often desirable to adjust the flow null of a servovalve independent
of other system parameters. The “mechanical null adjustment” on the Moog
G761/761 series servovalve allows at least ±20% adjustment of flow null.
The “mechanical null adjustor” is an eccentric bushing retainer pin located
above the “return” port designation on the valve body (see Figure 4) which, when
rotated, provides control of the bushing position. Mechanical feedback elements
position the spool relative to the valve body for a given input signal. Therefore, a
movement of the bushing relative to the body, changes the flow null.

Figure 4
Mechanical Null Adjustment

Figure 2

Figure 3
Sample
Nameplate

Mechanical Adjustment Procedure

Using a 3/8 inch offset box wrench, loosen the self-locking fitting until the
null adjustor pin can be rotated. (This should usually be less than 1/2 turn).
DO NOT remove self-locking fitting. Insert a 3/32 inch Allen wrench in null
adjustor pin. Use the 3/32 Allen wrench to rotate the mechanical null adjustor
pin to obtain desired flow null. Torque self-locking fitting to 57 inch lbs.

7. GENERAL SERVICING RECOMMENDATIONS

a. Disconnect the electrical lead to the servovalve.
b. Relieve the hydraulic system of residual pressure.
c. Remove the servovalve.

Important:

Local regulations may require precise hydraulic labeling on components!