Double-deck screens: sizing and trash removal in one pass
A screen with two decks grades the product into sizes and takes out coarse foreign material at the same time. Each size leaves through its own wide outlet.
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Two decks, three streams
The top deck has the largest openings. Coarse trash such as stems, stones or clumps stays on it and leaves at the end of the deck. Product that passes the top deck lands on the lower deck, which has smaller openings. The product that stays on the lower deck is one size fraction; what passes it is the smaller fraction, collected in the pan.
Wide outlets
Each fraction needs its own discharge. On food machines these outlets are made wide so that the product does not bridge or pile up at the chute, especially with sticky fruit such as figs or apricots.
Screen panels for the product group
The decks are stainless steel panels made for the product group. Opening size, shape and the free area of the panel are chosen according to the fruit and the sizes required at the outlet. A panel designed for one product is not simply moved to another.
When a single deck is enough
If the only task is to remove coarse trash and no grading is required, a single-deck screen with one set of openings does the job with a simpler machine. The double-deck version is chosen when grading into sizes is part of the process.
See also screening efficiency and sizing and selection.