Moog 77 K Series Installation And Operation Instruction

1. INTRODUCTION
This manual provides instructions and procedures necessary to install,
operate and troubleshoot the Moog 771K/772K/773K (simplified as 77XK)
intrinsic safety protected industrial servovalve. It is also applicable to Moog
Series 77X servovalves.
The 77XK series valves are electrical equipment for hazardous
areas requiring intrinsic safety or non-incendive protection. The approved
hazardous location markings include:
II 1 G Ex ia IIB/IIC T4 Ga KEMA 02ATEX 1015 X
II 3 G Ex ec IIC T4 Gc KEMA 02ATEX 1016 X
0344 per ATEX directive 2014/34/EU
Ex ia IIB/IIC T4 Ga IECEx KEM 10.0041X
Ex ec IIC T4 Gc IECEx KEM 10.0041X
per IECEx certification scheme.
The 77XK servovalves are also approved by FM, CSA, and TIIS for hazardous
locations. They are intended for directional, position, velocity, pressure and
force control in hydraulic control systems. Their standard fluorocarbon seals
provide compatibility with a wide variety of hydraulic fluids.
2. OPERATION
The Moog 77XK 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 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.
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 INTRINSICALLY
SAFE PROTECTION PERMIT NULL AND VOID.
77XK Series Installation and
Operation Instruction
Electrohydraulic Servovalve
Intrinsic Safety Protected
ELECTROHYDRAULIC VALVE CUT-AWAY
Magnet
(not shown)
Coil
Armature
Nozzle
Spool
Filter
P B
P B
Figure 1
Upper Polepiece
Flexure Sleeve
Lower Polepiece
Flapper
Feedback Wire
T A
T A Inlet Orifice