Moog 78N, 760N Installation And Operation Instruction Manual
1. INTRODUCTION
This manual provides the instructions and procedures necessary to install,
operate, and troubleshoot the Moog 78N and 760N series servo valves. The
78N and 760N series servo valves are electro hydraulic equipment for hazardous
locations requiring explosion proof protection. The approved hazardous location
markings include:
II 2 G Ex d IIA T3 Gb KEMA 02ATEX2322 X,
0344 per ATEX directive 2014/34/EU
Ex d IIA T3 Gb IECEx DEK 13.0029X
per IECEx certification scheme.
The 78N and 760N series servo valves are also approved by CSA and TIIS
for hazardous locations. They are intended for directional, position, velocity,
pressure, or force control in hydraulic control systems that operate with mineral
based fluids, or others upon request.
2. OPERATION
The Moog 78N and 760N Series Industrial Servo valves consist 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
78N/760N Series Installation
and Operation Instruction
Electrohydraulic Servo Valve
Explosion Proof
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 AND YIELD THE EXPLOSION
PROOF PROTECTION PERMIT NULL AND VOID.
(760N shown)
ELECTROHYDRAULIC VALVE CUT-AWAY
Magnet
Coil
Armature
Nozzle
Spool
Filter
Control Port B
Figure 1 Moog Series 760N
Control Port A
Tank
Pressure
Upper Polepiece
Flexure Tube
Flapper
Lower Polepiece
Feedback Wire
Inlet Orifice
3. ELECTRICAL INFORMATION
A wide choice of coils is available for a variety of rated current
requirements. The torque motor leads are individually attached to a flying lead
type explosion proof header so that external connections can provide series,
parallel, or single coil operation. Refer to the installation drawing of the specific
model servo valve for details. Servo valve coils should be driven with current to
provide consistency throughout the temperature range.
The 78N and 760N servo valves shall be installed for use with a metallic
conduit for the electrical leads. They are approved for explosion proof operation
with rated power of 0.28W maximum.
The 78N/760N servo valves are approved for explosion-proof protection
per EN 60079-0: 2012 and EN 60079-1: 2007 for ATEX and IEC 60079-0:
2011 and IEC 60079-1: 2007 for IECEx. Contact Moog for information on the
dimensions of the flameproof joints.
The socket head capscrews that attach the electrical connector and the
motor cap must have a thread conforming to ISO 262 and be of assembly class
fit 6g. The screw property class must be 10.9 minimum. The heads shall conform
to ISO 4762.
4. SPECIAL CONDITIONS FOR SAFE USE
The electrical connection of the permanently connected cable shall
be made in a certified enclosure in type of explosion protection flameproof
enclosure “d” or increased safety “e”.
For details on the flameproof joints contact MOOG Industrial Controls
Division. All fasteners must be of property class 10.9 minimum.
5. HYDRAULIC SYSTEM PREPARATION
To prolong servo valve 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 servo valve, the entire
hydraulic system should be purged of built-in contaminating particles by an
adequate flushing. The servo valve 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.
The mounting patterns and port locations of the servo valves are shown
on Figure 4. The servo valve should be mounted with socket head cap screws.
Apply a light film of oil to the screw threads and torque per Table 1.
Wire pigtail leads for desired coil configuration and polarity. Thread
conduit fitting to valve.
7. MECHANICAL NULL ADJUSTMENT
It is often desirable to adjust the flow null of a servo valve independent of
other system parameters. The “mechanical null adjustment” on the Moog 78N
and 760N Series servo valves allows at least ±20% adjustment of flow null.
The “mechanical null adjustor” is an eccentric bushing retainer pin
located above the “tank” 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
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.
Note:
Clockwise rotation of null adjustor pin produces flow from port P to port B.
Figure 2
Mechanical Null Adjustment
8. GENERAL SERVICING RECOMMENDATIONS
a. Disconnect the electrical lead to the servo valve.
b. Relieve the hydraulic system of residual pressure.
c. Remove the servo valve.
6. INSTALLATION
The Moog 78N and 760N series industrial servo valves may be mounted
in any position, provided the servo valve pressure, control and tank ports match
respective manifold ports.
2 Moog•78N/760NSeriesOperationInstruction•RevG08/18
78N Series 760N Series
Table 1
Mounting Screw 5/16-18 x 3.00 5/16-18 x 1.75
Size
Torque 120 in-lbs 96 in-lbs
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