Abstract: Paper making pulp stock being processed in a pulper is caused to flow through an auxiliary passageway from the main body of the pulper tub and back to the pulper tub at the downstream end of the passageway, propelled solely by the fluid dynamics of the vortical circulation in the pulper. The stock is first caused to flow through a diverging section of the passageway, whereby its velocity along the passageway is caused to decelerate, thence to a section of relatively large cross-section, where the velocity of the stock is low, and gravity classification takes place, and thence to a converging section of the passageway where its velocity is caused to accelerate before re-entering the main pulper tub.

Abstract: A centrifugal separator of the type commonly used in the papermaking industry is modified to discharge both the accept and reject flows from the smaller end of a frusto-conical chamber. The reject flow takes place through a peripheral opening and the accept flow through an axial opening. The method is also applicable to the separation of other fluid mixtures.

Abstract: The following invention discloses improvements in thickening devices used in the art of separating solid particles from liquids in a slurry of such particles and liquid having the method steps of causing an imperfectly filtered filtrate to flow by gravity to one outlet and a more perfectly filtered filtrate to flow by gravity toward another outlet.