POSITIONER MEETS CHALLENGE OF PRECISE CONTROL OF LARGE VALVES

Process Control Valves

Precise, accurate control of large valves across their entire operating range combined with the need for fast response times can sometimes be problematic. For example, in most process control applications, larger valves tend to 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 air from the actuator.

The air output capacity required to achieve fast positioning in larger actuators (with diaphragm areas of 1400 cm2 up to 2800 cm2) is simply too much for normal positioners and so positioning accuracy can be compromised.  In these situations the positioner controls a volume booster which achieves a much higher air output capacity than the positioner. Consequently this results in an overshoot on responding to small signal changes.

A solution to the problem is a control valve positioner package from control valve specialists SAMSON CONTROLS which facilitates exact positioning with fast response times over the entire operating range. The new Samson positioner package, which consists of a positioner and a special hook-up of several volume boosters with different air output capacities, accomplishes this task. Closing and opening times of less than two seconds can be achieved over the entire positioning range. This package has already been used successfully for compressor bypass valves (anti-surge valves) as well as in petrochemical applications involving adsorption processes in moving-bed adsorbers. 

For more information and product literature contact;

Samson Controls (London) Ltd, Redhill, Surrey, RH1 5JQ
Tel: 01737 766391 Fax: 01737 765472.