are used to separate groups of particulate materials by allowing the particulates to float or settle through two columns filled with water the columns have water flowing upward at different velocities or water flowing upward through one column and stagnant water in the other column application_number US 57622595 A description referring to fig1 the apparatus consists of two nearly vertical columns 1 and 2 column 1 is connected to column 2 through an entry port 3 which is below the top of column 2 and at least 6 inches above the bottom end 4 of column 2 such that particles falling through column 1 will enter column 2 at some point between the top and bottom of column 2 water inlets 5 and 6 allow water flow to be introduced into column 2 at points between port 3 and bottom end 4 water may be introduced through just one or a multitude of inlet points the bottom of column 2 has provisions that allow for the removal of heavy particles collecting there either on a continuous basis via mechanical means such as a bucket elevator or an auger or intermittently via a clean out plug or a discharge valve 14 as shown heights of the water levels 8 and 9 in the two columns are such that when water flow is initiated most or all of the incoming flow goes out through weir 7 as shown at the top of column 2 effective height of water level 9 in.