A control valve comprising: an electric controller having a drive stem; a flow control member; a piston assembly positioned in a bonnet of a fluid valve, the piston assembly to selectively couple said electric controller and the flow control member to control fluid flow through the fluid valve when electric power is provided to the electric controller, the piston assembly to operatively decouple the electric controller and the flow control member when electric power is not provided to the electric controller, the piston assembly comprising: a first piston; a first opening formed in a first surface of the first piston, the first opening is adapted to couple the first piston to the drive stem of the electric flow controller; a second piston slidably coupled to the first piston, the first piston and the second piston to move together as a unitary piston when electric power is provided to the electric controller and the second piston is to move relative to the first piston when electric power is not provided to the electric controller; and a fluid chamber formed between the first piston and the second piston, wherein the fluid chamber receives a control fluid to operatively couple the first and second pistons (342, 344) when electric power is provided to the electric controller, the control fluid being removable from the chamber to operatively decouple the first and second pistons (342, 344) to enable the second piston to move relative to the first piston when electric power is not provided to the electric controller; characterized in that a first stem protrudes from a second surface of the first piston, the second surface being opposite the first surface of the first piston; and in that the second piston is slidably coupled to the first piston via the first stem. an electric controller having a drive stem; a flow control member; a piston assembly positioned in a bonnet of a fluid valve, the piston assembly to selectively couple said electric controller and the flow control member to control fluid flow through the fluid valve when electric power is provided to the electric controller, the piston assembly to operatively decouple the electric controller and the flow control member when electric power is not provided to the electric controller, the piston assembly comprising: a first piston; a first opening formed in a first surface of the first piston, the first opening is adapted to couple the first piston to the drive stem of the electric flow controller; a second piston slidably coupled to the first piston, the first piston and the second piston to move together as a unitary piston when electric power is provided to the electric controller and the second piston is to move relative to the first piston when electric power is not provided to the electric controller; and a fluid chamber formed between the first piston and the second piston, wherein the fluid chamber receives a control fluid to operatively couple the first and second pistons (342, 344) when electric power is provided to the electric controller, the control fluid being removable from the chamber to operatively decouple the first and second pistons (342, 344) to enable the second piston to move relative to the first piston when electric power is not provided to the electric controller; characterized in that a first stem protrudes from a second surface of the first piston, the second surface being opposite the first surface of the first piston; and in that the second piston is slidably coupled to the first piston via the first stem. a first piston; a first opening formed in a first surface of the first piston, the first opening is adapted to couple the first piston to the drive stem of the electric flow controller; a second piston slidably coupled to the first piston, the first piston and the second piston to move together as a unitary piston when electric power is provided to the electric controller and the second piston is to move relative to the first piston when electric power is not provided to the electric controller; and a fluid chamber formed between the first piston and the second piston, wherein the fluid chamber receives a control fluid to operatively couple the first and second pistons (342, 344) when electric power is provided to the electric controller, the control fluid being removable from the chamber to operatively decouple the first and second pistons (342, 344) to enable the second piston to move relative to the first piston when electric power is not provided to the electric controller; characterized in that a first stem protrudes from a second surface of the first piston, the second surface being opposite the first surface of the first piston; and in that the second piston is slidably coupled to the first piston via the first stem.