Patent ID: 8622072

Claim:
A dual-stage fluid flow control apparatus, comprising: a signal stage having a proportional output, the signal stage having a signal stage relay including a supply plug having a first end adjacent a valve seat and a second end adjacent an exhaust seat, a signal stage input post adapted to couple the signal stage to a control device, a first biasing element to urge a seat load across the supply plug toward either the valve seat or the exhaust seat, and a second biasing element to bias the exhaust seat away from the second end of the supply plug; and an amplifier stage having an amplifier stage relay operatively connected to the signal stage via a signal passage, the amplifier stage having a fluid supply responsive member adapted to move a relay member to provide an amplified fluid supply output such that a shift in the seat load across the valve seat and the exhaust seat provides a predetermined engagement of either the valve seat to the first end of the supply plug or the exhaust seat to the second end of the supply plug to provide either a proportional or snap-acting and a direct or reverse acting output of the amplifier stage relative to an input signal at the signal stage input post.