Precise, accurate control of large
valves across their entire operating
range can sometimes be problematic.

Larger valves tend to be fitted with
pneumatic actuators, which provide
significant positioning forces. The
positioner is used to precisely
position the valve by filling the
actuator with the corresponding
amount of air, or by venting air from
the actuator. The positioner controls
a volume booster which achieves a
much higher air output capacity
than the positioner. This results in an
overshoot on responding to small
signal changes.

A solution to the problem is a
control valve positioner package
from Samson Controls, which
facilitates exact positioning with fast
response times over the entire
operating range. The package, which
consists of a positioner and a special
hook-up of several volume boosters
with different air output capacities,
can achieve closing and opening
times of less than two seconds over
the entire positioning range.