Azbil FloWing VFR - 4-2-2: Operating principle

Valve Positioner Azbil Corporation
4-4 Model VFR - FloWing Eccentric Rotary type Control Valves
4-2-2 : Operating principle
The valve positioner employs a force balance mechanism. See Figure 4-7 and Figure
4-8 for its operating principle.
Pneumatic input signal
from controller
Input
bellows
and lever
Nozzle
and
apper
Pilot
relay
Valve
body
Cam
Cam
follower
Feedback
spring
VR type
actuator
Force
Force
(+)
(-)
V
alve opening
Nozzle back pressure
Output pressure
Figure 4-7 Block diagram of the positioner
Nozzle back
pressure
Lever
F
eedback
springInput air
pressure
Nozzle
Restriction
Pilot relay
Output pressure
Actuator
Diaphragm
Spring
Actuator stem
Plug
Seat ring
Cam
Cam follower
Valve stem
Supply
air
pressur
e
Figure 4-8 Operating principle of the positioner