High flow, low hold up filters
View Patent ↗Filter devices with a flow director surrounded by a filter element providing a large filter surface area and low fluid volumes for efficient filtration and high recovery of sample fluids. The filter device can be configured with dimensions and sealing surfaces to functionally interact as a pre-filter for common usage disposable filter flasks.
1. A filter device comprising:
a filter element surrounding a central axis and comprising a top end, a bottom end, an external filter surface, an internal filter surface, and an internal space between the central axis and internal surface; and,
a flow director impermeable to liquids and comprising a top end and a bottom end and positioned within the internal space;
wherein the filter element is closer to the central axis at its bottom end than at its top end, and configured to provide more internal space cross-section between the filter and flow director at the top end of the filter than at the bottom end of the filter;
wherein a reservoir is positioned above the filter top end in fluid contact and hermetically sealed to the filter top end; and,
wherein the flow director is mounted within the inner space and comprises a smaller cross-section at the flow director top end than a cross-section at the flow director bottom end.
2. The device of claim 1 , wherein the filter is a pleated filter.
3. The device of claim 1 , wherein the filter is conical, or splayed outward toward the top.
4. The device of claim 1 , wherein the flow director has a parabolic cross-section in a plane through the central axis.
5. The device of claim 1 , wherein the reservoir is hermetically sealed to the filter top end through a shoulder flange extending radially out from the filter top end in a plane substantially perpendicular to the central axis.
6. The device of claim 1 , further comprising a shoulder flange extending radially out from the filter top end in a plane perpendicular to the central axis.
7. The device of claim 1 , wherein a bottom end of the flow director comprises a lateral flange extending out radially, which flange comprises a top surface in sealing contact with the filter bottom end.
8. The device of claim 1 , positioned in a reservoir of a vacuum filter apparatus.
9. The device of claim 1 , further comprising a separate or removable central sleeve shaped to fit into an interior space between the filter element and the flow director, whereby positioning the sleeve into the interior space displaces sample up to provide improved contact with the filter element.
10. The filter of claim 1 , wherein a vertical cross-section through the flow director tapers in from bottom to top.
11. The filter of claim 1 , wherein a radial distance between the flow director top end and the filter is at least two times a radial distance between the flow director bottom end and the filter.
12. The filter of claim 1 , wherein the top end of the flow director is at least 0.5 inch below the filter top end, and the bottom end of the flow director is not more than 0.25 inch from the filter bottom end.
13. The filter device of claim 1 , mounted within a receiver of a disposable filter flask having a filter flask filter with an average filter pore size at least 50% less than an average pore size of the filter device filter element.
14. The filter device of claim 1 , further comprising a prefilter (depth filter) element extending across the filter device sample reservoir positioned to prefilter sample before it contacts the filter element.
15. The filter device of claim 1 , wherein the device is configured so that a sample liquid applied to the flow director top end wets the filter top end.
16. The filter device of claim 1 , wherein the flow director contacts the filter element at most only at the filter bottom end.
17. The filter of claim 1 , wherein the flow director takes up between 80% and 40% of the filter internal space.