Filtration assembly and system

1. A filter comprising:

an upstream side defining a first aperture;

a downstream wall comprising filter media, a length of the filter extending between the upstream side and the downstream wall;

at least one side wall comprising filter media and extending lengthwise between the upstream side and the downstream wall,

wherein the upstream side, the downstream wall, and the at least one side wall together define an inner plenum in flowable communication with the first aperture;

wherein the inner plenum has a cross-sectional area extending crosswise of the filter, the cross-sectional area decreasing from adjacent the upstream side toward to downstream wall to a contracted location disposed intermediate the upstream side and the downstream wall, the cross-sectional area of the inner plenum increasing from adjacent the contracted location toward the downstream wall;

a contracting retainer attached to the at least one side wall at the contracted location and extending through the at least one side wall and into the inner plenum, the contracting retainer configured to retain the cross-sectional area of the inner plenum at the contracted location.

2. The filter according to claim 1 , wherein the inner plenum has a generally hourglass shape in longitudinal section.

3. The filter according to claim 1 , wherein the at least one side wall defines a second aperture at the contracted location, the first aperture having a cross-sectional area greater than a cross-sectional area of the second aperture.

4. The filter according to claim 1 , further comprising a frame attached to the upstream side.

5. The filter according to claim 4 , wherein the frame at least partially surrounds the first aperture.

6. The filter according to claim 1 , wherein the contracting retainer comprises at least one vane in the inner plenum.

7. The filter according to claim 6 , wherein the at least one vane comprises a plurality of vanes.

8. The filter according to claim 1 , wherein the cross-sectional area of the inner plenum tapers from the upstream side toward to the contracted location, wherein the cross-sectional area of the inner plenum tapers from the downstream wall to the contracted location.

9. The filter according to claim 1 , wherein the at least one side wall includes first and second side walls opposing one another, and third and fourth side walls opposing one another, wherein the contracting retainer is attached to and extends through the first and second side walls.

10. The filter according to claim 9 , wherein the contracting retainer comprises a plurality of contracting retainers attached to and extending through the first and second side walls, wherein the contracting retainers are spaced apart from one another between the third and fourth side walls.

11. The filter according to claim 9 , wherein the third and fourth side wall are free from the contracting retainer.

12. The filter according to claim 9 , wherein the first and second side walls extend inward toward one another from the upstream side toward the contracted location.

13. The filter according to claim 12 , wherein the third and fourth sides are generally parallel to one another from the upstream side toward the contracted location.

14. The filter according to claim 13 , wherein the first and second side walls extend outward away from one another from the contracted location toward the downstream wall.

15. The filter according to claim 14 , wherein the third and fourth sides are generally parallel to one another from the contracted location toward the downstream wall.

16. The filter according to claim 1 , wherein the at least one side wall defines opposing first and second inner surfaces, wherein the contracting retainer extends between the opposing first and second inner surfaces within the inner plenum.

17. The filter according to claim 16 , wherein the contracting retainer comprises a fastener extending between the opposing first and second inner surfaces within the inner plenum.

18. The filter according to claim 17 , wherein the fastener comprises a plurality of fasteners extending between the opposing first and second inner surfaces within the inner plenum, wherein the fasteners are spaced apart from one another within the inner plenum.

19. The filter according to claim 1 , wherein the contracting retainer comprises a fastener attached to the at least one side wall at the contracted location and extending through the at least one side wall and into the inner plenum.

20. The filter according to claim 19 , wherein the fastener is configured to resist adherence to particulate.

21. A filter comprising:

an upstream side defining a first aperture;

a downstream wall comprising filter media, a length of the filter extending between the upstream side and the downstream wall;

at least one side wall comprising filter media and extending lengthwise between the upstream side and the downstream wall, the at least one side wall having an exterior;

wherein the upstream side, the downstream wall, and the at least one side wall together define an inner plenum in flowable communication with the first aperture;

wherein the inner plenum has a cross-sectional area extending crosswise of the filter, the cross-sectional area decreasing from adjacent the upstream side toward to downstream wall to a contracted location disposed intermediate the upstream side and the downstream wall, the cross-sectional area of the inner plenum increasing from adjacent the contracted location toward the downstream wall; and

a contracting retainer attached to the at least one side wall at the contracted location, the contracting retainer configured to retain the cross-sectional area of the inner plenum at the contracted location, wherein the contracting retainer surrounds the exterior of the at least one side wall.

22. The filter according to claim 21 , wherein the contracting retainer comprises a band.

23. The filter according to claim 22 , wherein the band is rigid.

24. The filter according to claim 22 , wherein the band is flexible.

25. A filter comprising:

an upstream side defining a first aperture;

a downstream wall comprising filter media, a length of the filter extending between the upstream side and the downstream wall;

at least one side wall comprising filter media and extending lengthwise between the upstream side and the downstream wall, wherein the at least one side wall defines first and second opposing inner surfaces;

wherein the upstream side, the downstream wall, and the at least one side wall together define an inner plenum in flowable communication with the first aperture;

wherein the inner plenum has a cross-sectional area extending crosswise of the filter, the cross-sectional area decreasing from adjacent the upstream side toward to downstream wall to a contracted location disposed intermediate the upstream side and the downstream wall, the cross-sectional area of the inner plenum increasing from adjacent the contracted location toward the downstream wall;

a contracting retainer attached to the at least one side wall and extending between the opposing first and second inner surfaces within the inner plenum at the contracted location, the contracting retainer configured to retain the cross-sectional area of the inner plenum at the contracted location.

26. The filter according to claim 25 , wherein the contracting retainer comprises a fastener attached to the at least one side wall and extending between the opposing first and second inner surfaces within the inner plenum at the contracted location.

27. The filter according to claim 26 , wherein the fastener comprises a plurality of fasteners spaced apart from one another within the inner plenum at the contracted location.

28. The filter according to claim 25 , wherein the fastener comprises a vane attached to the at least one side wall and extending between the opposing first and second inner surfaces within the inner plenum at the contracted location.