MOOG 730 Series Servo Valves

PRODUCT OVERVIEW

The 730 Series flow control servo valves are throttle valves for 3 and

preferably 4-way applications. They are a high performance, 2-stage design

that covers the range of rated flows from 4 to 57 l/min (1 to 15 gpm) at 35

bar (500 psi) valve pressure drop per spool land.

The output stage is a closed center, four-way sliding spool. The pilot stage

is a symmetrical double-nozzle and flapper, driven by a double air gap, dry

torque motor. Mechanical feedback of spool position is pro vid ed by a

cantilever spring. The valve design is simple and rugged for de pendable,

long life op era tion.

These valves are suitable for electrohydraulic position, speed, pressure or

force control systems with high dynamic response requirements. The 730

is ideally suited for applications in the 4 to 57 l/min (1 to 15 gpm) requirements

when superior dynamics are a must.

FEATURES AND BENEFITS

The 730 Series is proven technology that performs reliably in machines

where high performance, stability and accuracy are required. Moog’s

Mechanical Feedback Valves are designed to provide high reliability and long

service life.

DESCRIPTION OF OPERATION

The 730 Series Flow Control Servo Valve 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 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 the nozzles, creating two variable orifices between

the nozzle tips and the flapper. The pressures controlled by the flapper

and nozzle variable orifices are 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 cantilevered 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 differential pressure at the spool ends, and the resulting

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.

ELECTRICAL DATA

Rated current and coil resistance

A variety of coils are available for 730 Series Servo Valves, which offer a

wide choice of rated currents.

Coil impedance

The resistance and inductance of standard coils are given below. The 2 coils

in each Servo Valve are wound with equal turns giving a normal production

tolerance on coil resistance of ±10 %. Copper magnet wire is used, so the

coil resistance will vary significantly with temperature. The effects of coil

resistance changes can be essentially eliminated through use of a current

feedback servoamplifier having high output impedance.

Inductance is determined under pressurized operating conditions and is

greatly influenced by back electromagnetic forces of the torque motor.

These effects vary with most operating conditions, and vary greatly with

signal frequencies above 100 Hz. The apparent coil inductance values given

are determined at 50 Hz.