Azbil FloWing VFR - 4-2-3: Bypass cock

Azbil Corporation Valve Positioner
Model VFR - FloWing Eccentric Rotary type Control Valves 4-5
4-2-3 : Bypass cock
Function of bypass cock
The supply air bypass cock mechanism is provided on the bottom of the valve
positioner. It is used to switch between the “ON” for “operation with positioner” and
“SUP” for “operation with the supply air” as shown in Figure 4-9. When switched
to “SUP”, the supply air bypasses the pilot relay and it is fed directly to the actuator,
thereby enabling the following two things:
(1) The valve opening can be directly controlled by the supply air.
(2) As the pilot relay is isolated from the supply air and output air, the pilot relay can
be inspected or serviced simply by shutting o the input signal air.
Piolot
relay
ON
Supply air
pressure
Output air
pressur
e
Piolot
relay
SUP
SUP
Supply air
pressure
Output air
pressure
Bypass cocks
ON
Positioner operative
Positioner operative
Supply air pressure by passed
Supply air pressure by passed
Figure 4-9 Switching by bypass cock
Installing the bypass cock
To install the bypass cock which has
been removed for gasket replacement
or some other servicing, install it
while referring to Figure 4-10. In this
case, apply silicone grease sparingly
to the surfaces of the gasket. If a new
gasket is to be used, place it so that
its white surface faces out. After fully
tightening the mounting screw (cross-
hole head), loosen it by a l/3 to l/4
turn.
Figure 4-10 Exploded view of the bypass cock