MTS Series 252 Servovalves - Manual (Page 15)

Servovalve Function
Series 252 Servovalve Product Information Introduction 15
Functional Diagram
Moving the spool A command from the controller causes the armature to rotate clockwise or
counterclockwise (depending on the polarity of the command). The command
causes the flapper to block one of the nozzles, which diverts hydraulic flow to
that end of the spool. The spool moves and opens hydraulic pressure to one
control port and the return line to the other control port. The control ports are
connected to each end of the actuator.
Stopping the spool The feedback wire works like a spring. The spool moves until the feedback wire
torque equals the torque from the magnetic forces. This causes the flapper to
move back toward the centered position. The spool stops at a position where the
feedback wire spring torque equals the torque input current of the command. The
spool position is proportional to the input command current.
Although the pressures are equal on both sides of the spool (so the spool is no
longer moving), control flow from the servovalve keeps the actuator moving.
First Stage
Armature
Nozzle
Second Stage
Spool
Filter
Manifold
Actuator
Piston
LVDT (inside rod)
Actuator Rod
Pressure
from Power
Fixed Orifice
Feedback Wire
Flapper
Lower Pole
Flexure Tube
Upper Pole Magnets Coil