Samson Control’s control valve positioner package is suitable for the problems sometimes associated with achieving precise control of large valves. 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 1400cm2 up to 2800cm2) 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 which achieves a much higher air capacity than the positioner and consequently results in an overshoot on responding to small signal changes. 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 less than two seconds can be achieved over the entire positioning range. Applications where the Samson package has been successful is for compress or bypass valves (anti-surge valves) as well as in petrochemical applications involving adsorption processes in moving-bed adsorbers.
