MOOG 743 Series Servo Valves

I.INTRODUCTION

This manual provides instructions and procedures necessary to install,

operate and troubleshoot the Moog 743 Series industrial serovalve.

Troubleshooting instructions are outlined so that only the specific component(s)

suspected of failure may be identified.

2. OPERATION

The Moog 743 Series Industrial Servovalve consists of a polarized electricaltorque motor and two stages of hydraulic power amplification .The motorarmature extends into the air gaps of the magnetic flux circuit and is supportedin 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 motorcoils surround the armature, one on each side of the flexure tube.The flapper of the first stage hydraulic amplifier is rigidly attached to themidpoint of the armature. The flapper extends through the flexure tube andpasses between two nozzles, creating two variable orifices between the nozzletips and the flapper.The pressure controlled by the flapper and nozzle variableorifice is fed to the end areas of the second stage spool.

The second stage is a conventional 4-way spool design in which outputflow from the valve, at a fioxed valve pressure drop, is proportional to spooldisplacement from the null position.A cantilever feedback spring is fixed to theflapper and engages a slot at the center of the spool. Displacement of the spooldeflects 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 flexuretube 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 theother and results in spool displacement. The spool displacement transmits aforce in the feedback wire which opposes the original input signal torque. Spoolmovement continues until the feedback wire force equals the input signal force.

3. HYDRAULIC SYSTEM PREPARATION

To prolong servovalve operational life and to reduce hydraulic systemmaintenance, it is recommended that the hydraulic fluid be kept at acleanliness level of ISO DIS 4406 Code 16/13 maximum, 14/11recommended. The most effective filtration scheme incorporates the use ofa kidney loop or "off-line" filtration as one of the major filtrationcomponents. The filter for the "off-line" filtration scheme should be a B2275filter for maximum effectiveness.

Upon system startup and prior to mounting the servovalve, the entirehydraulic system should be purged of built-in contaminating particles by anadequate flushing. The servovalve should be replaced by a flushing manifoldand the hydraulic circuit powered up under conditions of fluid temperatureand fluid velocity, reasonably simulating normal operating conditions. Newsystem filters are installed during the flushing process whenever thepressure drop across the filter element becomes excessive. The flushingprocesses should turn over the fluid in the reservoir between fifty to onehundred times.

4.INSTALLATION

The Moog 743 series industrial servovalve may be mounted in anyposition, provided the servovalve pressure, piston and return ports match

respective manifold ports.

The mounting pattern and port location of the servovalve is shown onFigure 4.The servovalve should be mounted with 5/16-18 x 2.50 inch long,socket head cap screws.Apply a light film of oil to the screw threads andtorque to 96 inch pounds.

Wire mating connector for desired coil configuration and polarity.

Thread connector to valve.

To maintain a clean hydraulic system, the filters must be replaced on aperiodic basis. It is best to monitor the pressure drop across the filterassembly and replace the filter element when the pressure drop becomesexcessive. In addition to other filters that are installed in the hydrauliccircuit, it is recommended that a large capacity. low pressure By275 filter beinstalled in the return line. This filter will increase the interval between filterelement replacement and greatly reduce the system contamination level.