Embodiments of the invention provide a piston assembly for a control valve in a water softener system. The control valve includes a drive mechanism, one or more fluid passageways, and a seal assembly. The piston assembly includes a main piston moveably received within the seal assembly and including a first end and a second end opposite to the first end, and a shuttle piston moveably received within the seal assembly. The shuttle piston includes a first end and a second end opposite to the first end, and is configured to selectively engage the second end of the main piston to form a seal therebetween and to selectively move relative to the second end of the main piston to form an opening between the second end of the main piston and the first end of the shuttle piston, in response to movement of the main piston.