Moog 72 Installation And Operation Instruction Manual

72 Series Installation and

Operation Instruction

1. INTRODUCTION

This manual provides instructions and procedures necessary
to install, operate and troubleshoot the Moog Series 72 Electrohydraulic
Industrial Servovalve.Troubleshooting instructions are outlined to permit the
identification of the specific component(s) suspected of failure.

2. OPERATION

The Moog Series 72 Electrohydraulic Servovalve consists of a polarized
electrical torque motor and two stages of hydraulic power amplification (see
Figure 1).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 causes 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

Polepiece

Connector

Filter

Feedback Wire

Spool

Supply Pressure

Figure 1 Moog Series 72

B

A

Return

Nozzle

Coil
Armature

Magnet
Flexure Tube
Inlet

Orifice

Filter

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 72 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 5. The servovalve should be mounted with 3/8-16 x 2.00 inch long,
socket head cap screws.Apply a light film of oil to the screw threads and
torque to 175 inch-pounds.

Wire the mating electrical connector for desired coil configuration and
polarity (see 72 Series Servovalve catalog, CDL6266). 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
72 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.

Tools and Equipment

a. Blade screwdriver

3

3

64,

b. Allen wrench set (3/32,7/

8,

/

/16)
c. No. 4-40 NC by 11/2inch screw,1/4 -28 UNF x 1 inch screw
d. Torque wrenches
e.3/8 inch offset box wrench
f. Tweezers

Figure 2
Mechanical Null Adjustment

6.PROCEDURE TO CONFIGURE A 72 SERIES SERVOVALVE
FOR EXTERNAL PILOT OPERATION (see figure 3)

a. Remove the set screw from the “X” port on the base of the valve using a

1/8” Allen wrench.

b. Thread a #2-56 screw into the O-Ring plug that is now visible and remove

it form the “X” port.

c. Remove the four socket head cap screws and lockwashers that retain the

cover plate for the field replaceable filter using a 5/32” allen wrench.

d. Use one of the screws to pull the filter and filter housing out of the filter

cavity of the body.The filter housing has two O-Rings on its O.D..The

housing will come part way out then stop after the second O-Ring passes

the internal relief in the body.At this time it may be easier to remove the

visible O-Ring and carefully pry the housing and filter out with two

opposing flat blade screw drivers, than to continue pulling on the screw. Be

careful not to damage the O-Ring groove.

e. A bore will be visible inside the body cavity where the O-Ring plug must

be inserted.

f. Retain the O-Ring plug with the set screw.

g. Re-install the filter and filter housing in the cavity.

h. Re-install the filter cover, retaining screws and lockwashers.Torque the

screws to 85-in-lbs.

Internal

External

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.

2 Moog • 72 Series Operation Instruction • RevE 04/07

Figure 3

X Port

Pressure Port

7. GENERAL SERVICING RECOMMENDATIONS

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