The document describes the construction and operation of a servo valve. It is constructed with a body that houses a sleeve and spool to control fluid flow. A filter and pilot supply are integrated into the body to regulate fluid to the pilot stage, which includes two nozzles and a torque motor. The torque motor controls a flapper plate which unbalances pressures on either side of the main spool when energized, causing fluid flow through the valve.

1. SERVO VALVE - BODY
Construction of the
servo valve starts with
the body.
Construction of the
servo valve starts with
the body.

2. SERVO VALVE SLEEVE
The body is fitted with
a sleeve in order that
the spool lands can be
accurately matched to
the sleeve ports.
The body is fitted with
a sleeve in order that
the spool lands can be
accurately matched to
the sleeve ports.

3. SERVO VALVE - SPOOL
The body is fitted with
a sleeve in order that
the spool lands can be
accurately matched to
the sleeve ports.
The body is fitted with
a sleeve in order that
the spool lands can be
accurately matched to
the sleeve ports.

4. SERVO VALVE - PILOT FILTER
A filter for the pilot
supply is also fitted in
the main body.
A filter for the pilot
supply is also fitted in
the main body.

5. SERVO VALVE - PILOT SUPPLY
The body end-caps are
used to connect pilot oil
from the filter to the
pilot stage of the valve.
The body end-caps are
used to connect pilot oil
from the filter to the
pilot stage of the valve.

6. SERVO VALVE - NOZZLE BLOCK

7. SERVO VALVE - PILOT NOZZLES
The pilot stage includes
two nozzles ...
The pilot stage includes
two nozzles ...

8. SERVO VALVE - TORQUE MOTOR
... and a torque motor.
Attached to the torque
motor armature is a
flapper plate which
extends down through
the two pilot nozzles
and locates in a recess
in the main spool.
... and a torque motor.
Attached to the torque
motor armature is a
flapper plate which
extends down through
the two pilot nozzles
and locates in a recess
in the main spool.

9. SERVO VALVE
When the valve is de-
energised, the flapper
is centred relative to
the two pilot nozzles so
pressures on either end
of the main spool are
equal and the main spool
is also centred.
When the valve is de-
energised, the flapper
is centred relative to
the two pilot nozzles so
pressures on either end
of the main spool are
equal and the main spool
is also centred.

10. SERVO VALVE
The torque motor is
fitted with a permanent
magnet frame
surrounding the
armature.
The torque motor is
fitted with a permanent
magnet frame
surrounding the
armature.

11. SERVO VALVE
Passing a current
through the torque
motor coils magentises
the armature and
causes it to tilt. The
direction of the tilt is
determined by the
voltage polarity and the
amount of tilt by the
magnitude of the
current.
Passing a current
through the torque
motor coils magentises
the armature and
causes it to tilt. The
direction of the tilt is
determined by the
voltage polarity and the
amount of tilt by the
magnitude of the
current.

12. SERVO VALVE
The tilting of the
armature causes the
flapper to move closer
to one nozzle and
further away from the
opposite nozzle.
The tilting of the
armature causes the
flapper to move closer
to one nozzle and
further away from the
opposite nozzle.

13. SERVO VALVE
This unbalances the
pressures on either end
of the main spool ...
This unbalances the
pressures on either end
of the main spool ...

14. SERVO VALVE
... causing the main spool
to move and flow to
pass through the valve.
As the main spool
moves, the flapper is
dragged back to the
centre of the two
nozzles when the pilot
pressures equalise and
the spool stops moving.
... causing the main spool
to move and flow to
pass through the valve.
As the main spool
moves, the flapper is
dragged back to the
centre of the two
nozzles when the pilot
pressures equalise and
the spool stops moving.

15. SERVO VALVE