Mark Urban produced two valves that constituted his Flowreversal Technology System. The above plumbing diagram shows how Mark's X-m and T-m valves were plumbed into a pool to create his unique Flowreversal System for swimming pools.
Flowreversal Valve + Proportioning Valve = Mark Urban's Flowreversal System
The Palmer Flowreversal Module is a replacement for Mark Urban's Flowreversal System now that Mark's X-Body and T-Body valves are no longer available.