For example, in most process control applications, larger valves tend to be fitted with pneumatic actuators, which provide significant positioning forces. In these situations, the positioner is used to precisely position the valve by filling the actuator with the corresponding amount of air, or by venting from the actuator.
However, as a result, the air output capacity required to achieve fast positioning in larger actuators (with diaphragm areas of 1,400cm2 up to 2,800cm2) is simply too much for normal positioners and so accuracy can be compromised. Also, an added complication in these situations is that the positioner controls a volume booster that achieves a much higher air capacity than the positioner and consequently results in an overshoot on responding to small signal changes.
The manufacturer says its control valve positioner can achieve exact positioning with fast response times over the entire operating range. The package consists of a positioner and a special hook-up of several volume boosters with different air output capacities, which perform this task. Closing and opening times of under two seconds can be achieved over the entire range.
Contact: Samson Controls