Moog 79 Series (79-200) Servo Valves

1. INTRODUCTION

This manual provides instructions and procedures necessary

to install, operate and troubleshoot the Moog Inc. Series 79 Industrial

Servovalve. Loop closure of the third stage spool requires external electronics

consult factory for suggested Moog model numbers.

2. OPERATION

The Moog Inc. Series 79-200 Industrial Servovalve consists of a two stage

mechanical feedback pilot valve and a high flow third stage with electrical

feedback. Proper operation requires the use of user provided electronics to

condition the spool position transducer, compare actual spool position to

command and to generate a current signal to the pilot valve.

In a typical system, a spool position command signal is compared to the

actual spool position signal in the servoamplifier.The error (difference) is

converted to a current signal and used to drive the pilot valve spool in the

proper direction.The pilot valve spool directs oil flow to one end of the third

stage spool, moving the spool. Spool movement is sensed by the spool position

transducer and spool motion continues until the spool position signal is equal

to the command signal.At this point, the servoamplifier current returns to near

zero, the pilot valve returns to null and the third stage spool is held in position.

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 79 Series Industrial Servovalve may be mounted in any position,

provided the servovalve pressure,control,and return ports match respective

manifold ports.

Caution: If the servovalve is mounted vertically,the third stage spool may drift

to one side when hydraulics are shut off.This may result in sudden movement of

equipment when starting up.

The mounting pattern and port location of the servovalve is shown on

Figure 2.The servovalve should be mounted with 5/8-11 x 2.5 inch long high

strength socket head capscrews.Apply a light film of oil to the screw threads

and torque to 215 foot pounds.

On selected models,the pilot valve supply and return may be supplied

through external lines attached to the valve body or an intermediate manifold.

High response valves with stub shafted spools will require the installation of a

drain line to the non transducer end cap.

Wire mating connector for desired coil configuration and polarity.Thread

connector to valve.Wire transducer according to the installation drawing,figure 2.

5.MECHANICAL NULL ADJUSTMENT

There is no mechanical null adjust.Typically,a bias potentiometer is

provided on the electronics to null the valve.If adjustment of the transducer is

required,refer to the proper steps below.

Non Stub Shafted valves and older model Stub Shafted valves: