Moog G761 Installation And Operation Instruction Manual

1. INTRODUCTION

This manual provides instructions and procedures necessary to install,
operate and troubleshoot the Moog G761 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 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.

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.

ELECTROHYDRAULIC VALVE CUT-AWAY

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.

Figure 1 Moog Series G761

Upper Polepiece

Flexure Tube

Lower Polepiece
Flapper

Inlet Orifice

Coil

Armature

Nozzle

Feedback Wire

Spool

PA T BP

x

Filter

G761 Series Installation and

Operation Instruction

Electrohydraulic Servovalve

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. INSTALLATION

The Moog G761 Series Industrial Servovalve may be mounted in any
position, provided the servovalve pressure, piston and return ports match
respective manifold ports.

The mounting pattern and port location of the servovalve is shown on
Figure 4.The servo-valve 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 mating connector for desired coil configuration and polarity. Thread
connector to valve.

5. MECHANICAL 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
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 2) 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.

Adjustment Procedure

a. Using a 3/32inch Allen wrench, rotate mechanical null adjustor pin to obtain
desired flow null. If excessive torque (more than 12 in.-lb.) is required to rotate
null adjustor pin, perform Step b.

Note:

Clockwise rotation of null adjustor pin produces open loop flow from port B to port A.

b. Using a 3/8inch offset box wrench, loosen self-locking fitting. DO NOT
remove self-locking fitting. Insert a 3/32inch Allen wrench in null adjustor pin.
Using the 3/8inch offset box wrench to tighten self-locking fitting until a torque
of 10 to 12 in.-lb. is required to rotate null adjustor pin with the Allen wrench.
Perform Step a to establish desired flow null.

Tools and Equipment
a. Allen wrench set (3/32inch)
b. Torque wrench (10-12 inch-pounds)
c.3/8inch offset box wrench

6.GENERAL SERVICING RECOMMENDATIONS

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

Table 1. Replacement Parts

Part Description Qty. Part Number

G761 Series Filter Replacement Kit 1 B52555RK201K1
Filter Plug - Body O-Ring (1) 2 42082-60
End Cap - body O-Ring (1) 2 42082-42
End Cap - Body O-ring (1) 2 42082-1
Filter Disc (1) 1 A67999-65
Base O-Rings 4 42082-22

1 42082-13

(1) Included in Filter Replacement Kit

Figure 2
Mechanical Null Adjustment