Electro-Pneumatic Positioner
YT-1000 / 1050 series
Product Manual
Ver. 1.30
41
3
principle of positioner movement
3.1
Linear Positioner
Fig. 3-1: Linear positioner with an actuator
When INPUT SIGNAL is supplied to the positioner to open the valve, power is generated from
①
the
torque motor and pushes
②
the flapper to the opposite side of
③
the nozzle. The gap between
③
the
nozzle and
②
the flapper becomes wider and from inner part of
④
the pilot, air inside
⑨
the chamber
is exhausted through
③
the nozzle. Due to this effect,
⑤
the spool moves to the right. Then the spool
pushes
⑧
the poppet away from
⑦
the seat which was blocked by the poppet and supplied pressure
(air) goes through
⑦
the seat and OUT1 Port and enters into
⑩
the chamber of the actuator. Then
⑩
chamber’s pressure will increase and when there is enough pressure inside the chamber to push
⑪
the actuator’s spring,
⑫
actuator’s stem will start to go down and through the feedback lever, stem’s
linear motion will be converted to span
⑭
lever’s rotary motion. This
⑭
span lever’s rotary motion will
then once again rotate
⑮
the span and pulls
⑯
the span spring. When the valve’s position reaches to
given input signal,
⑯
span spring’s pulling force and
①
torque motor’s power will be balanced and
move
②
the flapper back its original position to reduce the gap with
③
the nozzle. The amount of air
being exhausted through
③
the nozzle will reduce and
⑨
the chamber pressure will increase again.
⑤
Spool will move back to its original position on the left and
⑧
the poppet will also move in same
direction blocking
⑦
the seat to stop the air coming into the
⑩
chamber through the SUPPLY. As a
result, the actuator will stop operating and the positioner will return to its normal condition.