MOOG 72 Series Flow Control Servo Valves

PRODUCT OVERVIEW

The 72 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 95 to 225 l/min (25 to 60 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 eration.

These valves are suitable for electrohydraulic position,

speed, pressure or force control systems with high dynamic

response requirements.

The 72 Series is ideally suited for applications in the 95

to 225 l/min (25 to 60 gpm) when superior dynamics are a

must.

Intrinsically safe valve versions are available for use in

applications with potentially hazardous environments.

Specific models are certified to FM, ATEX, CSA, TIIS and

IECEx standards.

DESCRIPTION OF OPERATION

The 72 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. 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 cantilevered feedback spring is fixed to

the flapper and engages a slot at the center of the spool.

Displacement of the spool defects the feedback sprint

which creates a force on the armature/flapper assembly.

Input signals induce a magnetic charge in the armature

and cause 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.