Patent ID: 8002975

Claim:
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 an 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, said fluid inlet capable of introducing fluid into said upstream zone, said fluid outlet capable of releasing fluid from said downstream zone out of said housing; the upper filter layer is held by a substantially rigid framework, said upper filter layer and said substantially rigid framework combining to form an upper filter component, said upper filter layer comprising a pressure-activated gate integrated into only the upper filter layer, wherein the pressure-activated gate is a switchable gate capable of opening and closing comprising a plug and a gate, i) the plug including a plunger having a bladder attached to the first end of a stem, and a stopper surface attached to the second end of the stem wherein, a) when the pressure within the filtration device rises to the first predetermined pressure range the pressure within the lumen rises, the bladder compresses, the stopper surface elevates and the aperture in the gate opens to allow the non-selective passage of fluid from the upstream zone into the downstream zone, b) when the pressure within the filtration device falls below a second predetermined pressure range, the pressure within lumen falls, the bladder returns to its original size, and the stopper surface impedes the aperture in the gate to prevent the flow of fluid downstream through the gate; and ii) the gate having a lumen and an aperture; the plug is located within the lumen such that the aperture is open upon attainment of a first predetermined pressure range, and the aperture is closed when the pressure falls below a second predetermined pressure range the rearmost filter layer being positioned in said downstream zone, wherein a rearmost filter layer does not include a pressure activated gate.