Answer / alfred t jose

we can control the control valve accurately with the help of
positioner.

Answer / sam

There are applications where the positioner is actually
causing the process to run away, due to the valve reacting
being too fast, and the control will be much easier without
the positioner. You can do this by installing a I/P
converter, piped directly to the actuator.

In 99,99% of applications however, the positioner is
necessary to control the process since process changes is
normally very fast and smooth control will be impossible
without a positioner to speed up the reaction time of the
control valve and keeping the process on the desired control
set-point.
In these applications if you do not install a positioner you
will find that your process runs in a big sinuous wave form
and this will obviously cause a major chain reactions
through out the whole plant.
Good luck

Answer / ramesh dham

There are two works of positionar First is to boost up the pneumatic signal to desired spring range of actuator and second is to get mechanical feedback of valve stem to accurate control over valve.
if we do not use positionar then our valves spring range must lie between 3-15 psig also we can't control accurately the process with higher variation.

Answer / kkrameshkumar

Only the diaphragm actuator type control valves can be
operated without positioners provided that the spring range
of the actuator is within the range of control air pressure.

Cylinder actuator type control valves cannot be operated
proportionally without a positioner. only on/off can be
done.

With positioner we can achive the exact position of the
control valve with speed. If positioner is not there then
the actuation will be sluggish and we cannot get exact
postioning of control valve

Answer / guest

yes it will operate. but we have to see the actuator
pressure rating range between that range it will operate.
with positionar a valve can run smoothly but without a
positionar it will sluggish.

why 4 to 20 ma? why cant some other range?

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