The 3M Aqua-Pure V3011 Clack Valve Piston directs water through the control valve during regeneration, allowing water to cycle through its various stages to ensure continuous treated water. Made of brass and stainless steel, the piston assembly installs above the Clack WS1 control valve. The assembly serves as a buffer to protect the control valve. It also prevents scratches and damage to the valve housing and the deck plate.