A fluid actuated positioner adapted to receive a working fluid of constant pressure and to produce a mechanical output signal proportional to a fluid input signal from a signal fluid of varying pressure, the positioner having:
- (a) an input cylinder having input partition means dividing the cylinder into first and second input chambers, an input rod mounting the partition means for movement axially of the cylinder, the first input chamber receiving the signal fluid under varying pressure which generates a varying input signal on the input rod, and resilient means cooperating with the input rod to oppose the input signal on the input rod, the input rod being essentially unaffected by contact with the working fluid,
- (b) an output cylinder having an output member with an output partition means and an output rod, the output partition means dividing the output cylinder into first and second output chambers, the output partition means having first and second faces within the respective output chambers, the output rod mounting the output partition means for movement axially of the output cylinder, the first output chamber receiving the working fluid under a constant pressure which generates a first force on the output partition means, the output rod extending from the output partition means through the first output chamber so that the first face has a smaller effective area than the second face, and a fixed metering means disposed between exhaust and the second output chamber to control flow of working fluid therefrom prior to exhausting the working fluid,
- (c) a main control valve communicating with the first and second output chambers and having first and second valve portions, the first valve portion being a connecting bore within the output member, the connecting bore communicating with the first output chamber, and the second valve portion being a portion of the input rod which cooperates with the connecting bore to control fluid flow therethrough, so that relative positions of the output member and the input rod control metering of a continuous flow of working fluid passing between the first and second valve portions so as to control flow of working fluid from the first output chamber into the second output chamber prior to exhausting the working fluid from the positioner,
- so that the working fluid in the second output chamber generates a second force on the second face in opposition to the first force to produce on the output rod a resultant displacement proportional to the input signal.