The Multi-Step DI system consists of a three compartments column with each compartment holding different type of ion exchange resins.

For high purity water application, the most usual arrangement is to place a layer of strongly acidic cation resins in the bottom compartment, a layer of strongly basic anion resins in the middle compartment and a third layer of strongly acidic cation resin on the top compartment.

The multi-step process is based on an upflow/fluidized bed techniques.

Water enters the bottom of the column passes through the first cation resin layer, where the feed water cations will be replaced, then followed by the anion resin layer, where the feed water anions will be replaced.

The third layer is the polishing cation resin layer where traces of cations leaked through the first cation resin layer will be removed before water exiting the column from the top.