Abstract: Apparatus and method for removing particulate impurities from liquids wherein the liquid flows upward through a bundle of tubes having a helical shape to present an inclined path where settling of particulates back down the tube occurs. The bundle is preferably formed around a central standpipe. This modular helical tube bundle arrangement provides a compact and inexpensive structure and great convenience for maintenance. The preferred cross sectional shape of each tube is oval to increase settling rate. In order to form the tubes from rigid tubing, a concrete form is made in accordance with a procedure which includes forming a "tent" of strings, sculpting a plasticene negative form using the tent of strings as a guide, casting concrete against the form to produce a mold that resembles a sliding board with an outside drooping edge.

Abstract: A system for removing impurities from liquids wherein the liquid is forced upward through several zones, the first zone being a bundle of tubes having a helical shape to present an inclined path where settling of particulates back down the tube occurs, then through a stack of filter modules which are over the bundle of tubes and contain treatment media, the arrangement of the filter modules being such that the passage of fluid in the upward direction removes particulates before flushing through the treatment media and agitates the treatment media so as to prevent packing. The helical form of the settling tubes and the modular arrangement provides a compact and inexpensive structure and great convenience for maintenance. The preferred cross sectional shape of each tube is oval to increase settling rate.