MOOG 761 Series Flow Control Servo Valves

PRODUCT OVERVIEW

The 761 Series Flow Control Servo Valves are throttle valves for 3-way

and preferably 4-way applications. They are a high performance,

2-stage design that covers the range of rated flows from 0.5 to 75

l/min (0.125 to 19.5 gpm) at 35 bar (500 psi) valve pressure drop per

spool land.

The design is simple and rugged for dependable, long life operation.

The pilot stage is comprised of a symmetrical, nozzle-flapper torque

motor. The output stage includes a 4-land sliding spool, precision ground

to a bushing for optimal performance. A carbide tipped feedback wire

provides mechanical feedback of the spool position to the torque motor.

The carbide ball on the end of the feedback wire ensures high accuracy,

reliable operation and long service life. All of our Servo Valves are known

for high accuracy and reliable operation even in the harshest industrial

applications.

These valves are suitable for electrohydraulic position, speed, pressure

or force control systems with high dynamic response requirements.

The 761 Series is one of the most versatile servo valves suitable for a

broad range of applications. It is the latest version of the famous 760

series that incorporates about 70 years of Moog design expertise.

DESCRIPTION OF OPERATION

The 761 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 2 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 2 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 hole in 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.

The differential pressure created by this action causes spool motion.

The resulting spool displacement induces a linear 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.