The Amarcon Valve Positioner (AVP) is an instrument working on force balance Principle to Position the control Valve Stem in accordance to a Pneumatic Signal received from a controlling System, without the interface of the operating, and even actuator swing or unequal forces applied on the valve by nature.  For neutralizing this a positioner will balance all the forces to operate a control valve. Valve cv sizing calculator for liquids and gases flow systems.