| 1. A serial-flow filtration device comprising a housing, a fluid inlet, a fluid outlet, and a stack of serially-arranged filter
layers including at least an upper and a rearmost filter layer, and additional filter layer or layers between said upper and
rearmost layers, each filter layer comprised of a filter medium, the filter layers being made of the same or different selectively-permeable
filtration material, each adjacent filter layer being separated proximately either by an air space or by a spacer comprising
a screen capable of allowing substantially non-selective passage of fluid therethrough and laterally;
the upper filter layer dividing the interior of the housing into an upstream zone and a downstream zone, the fluid inlet capable
of introducing fluid into the upstream zone, the fluid outlet capable of releasing fluid from the downstream zone out of the
housing;
the upper filter layer comprising a hole and a pressure-activated gate integrated into said selectively-permeable filtration
material and covering the hole, wherein the pressure-activated gate comprises a plug friction-fitted into the hole provided
through the filter medium of the upper filter layer, the plug comprising a monolithic geometric solid cork to be blown through
the filter medium upon the attainment of a predetermined pressure differential, wherein the rearmost filter layer is not comprised
of a pressure activated gate.
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