Flow Control Ball

Autotrol

Rubber Ball – Used to regulate flow behind backwash plug and brine control dial.
Old part number 4F, and newer part number 1030502

Chlorine in the water supply can cause this part to swell and soften to the point that it will either block normal flow or get stuck and allow too much flow.
The ball behind the Brine Control Dial and the Back Wash Plug are identical.