Effective diffuser/thickener screen backflushing

A pulp treating apparatus comprising:

• a generally upright vessel defining an interior volume containing pulp to be treated;
• a pulp inlet to the vessel;
• a pulp outlet from the vessel, the pulp flowing generally vertically between the inlet and the outlet;
• a plurality of screens mounted within the vessel and connected to supporting liquid conduits;
• extraction means for withdrawing liquid from the pulp, through the screens, and through the conduits to a point outside the vessel;
• and
• screen backflushing means mounted within the vessel and including a chamber defining element having first and second ends, the first end in open communication with liquid in the liquid conduits, and the second end in open communication with the pulp within the interior volume of the vessel;
• a liquid engaging element mounted within said chamber defining element for relative reciprocal movement between said liquid engaging element and said chamber defining element;
• and means for effecting relative movement between said chamber defining element and said liquid engaging element to cause said liquid engaging, element to force liquid out of the chamber in one direction of relative movement between said elements, to effect backflushing, and take liquid into the chamber in another direction of relative movement therebetween.