Moog g77x, 77x, g771, 771, g772 Installation And Operation Instruction Manual

G77X/77X Series Installation

and Operation Instruction

1. INTRODUCTION

This manual provides instructions and procedures necessary
to install, operate and troubleshoot the Moog Inc.Series G771/G772/G773
(simplified as G77X) and 771/772/773 (simplified as 77X) Electrohydraulic
Industrial Servovalve.Troubleshooting instructions are outlined to permit the
identification of the specific component(s) suspected of failure.

2. OPERATION

The Moog G77X/77X 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.

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 four-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 to 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

Magnet

(not shown)

Coil

Armature

Nozzle

Spool

Filter

PB T A

Figure 1 Moog Series G77X/77X

Upper Polepiece

Flexure Sleeve

Lower Polepiece
Flapper
Feedback Wire

Inlet Orifice

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 ß3≥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
replacements and greatly reduce the system contamination level.

4. INSTALLATION

The Moog G77X/77X Series Industrial Servovalve may be mounted in any
position, provided the servovalve pressure, piston and return ports match
respective manifold ports.

The mounting pattern, port location and mounting bolts of the servovalve
are shown on Figure 4. Apply a light film of oil to the screw threads and torque
to 57 inch-pounds.

Wire mating connector for desired coil configuration and polarity.

Thread connector to valve.

Adjustment Procedure

Using a 3/8inch 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 3/32inch Allen wrench in null
adjustor pin. Use the 3/32Allen wrench to rotate the mechanical null adjustor
pin to obtain desired flow null.Torque self-locking fitting to 57 inch lbs.

Note:

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

Table 1. Replacement Parts

Part Description Qty. Part Number

G77X/77X Series Filter
Replacement Kit 1 B52555RK054K001
Inlet Orifice End Cap O-Rings (1) 2 42082-001
Inlet Orifice O-Rings (1) 2 42082-189
End Cap - Bushing O-Rings (1) 2 42082-042
Filter Tube (1) 1 C39486-005-060
End Cap - O-Rings (1) 2 42082-001
Base O-Rings

G771/771 4 42082-007
G772/772 4 42082-013
G773/773 4 42082-022

(1) Included in Filter Replacement Kit.

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
G77X/77X Series servovalve allows at least ±20% adjustment of flow null. The
“mechanical null adjustor” is an eccentric bushing retainer pin located above the
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.

Figure 2
Mechanical Null Adjustment

6. GENERAL SERVICING RECOMMENDATIONS

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