US Patent 9328525 Pool cleaning apparatus

A pool cleaning apparatus that may include a filter; a entrapment cell; a first impeller; a first pump motor arranged to rotate the first impeller; a driving unit arranged to move the pool cleaning robot; a structural element; and an external housing that comprises a first inlet and a first outlet; wherein the filter and the structural element define a first space that has a spiral portion; wherein the first impeller is arranged to rotate along a first rotational direction; wherein rotation of the first impeller along a first rotational direction causes fluid be drawn through the first inlet and to follow a spiral path within the first space during which a first portion of the fluid is filtered by the filter to provide filtered fluid that exits through the first outlet of the housing; and a second portion of the fluid follows the spiral path until entering the entrapment cell.