MOOG 631 Series Servo Valves

PRODUCT OVERVIEW

The 631 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 5 to 75 l/min (1.3 to 20 gpm) at 35 bar

(500 psi) valve 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.

FEATURES AND BENEFITS

The 631 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 631 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 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 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 signals induce 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.