Filter element

1. A filter element for filtering impurities from air, the filter element comprising one or more filters,

wherein each of the one or more filters is composed of a filter frame that is connected to one or more filter bags, wherein the filter frame comprises one or more inflow openings through which air with said impurities to be filtered flows, and each of the one or more filter bags includes a first end which is open and fastened to the inflow opening and a second end which is closed;

wherein each of the one or more filter bags respectively extends in length along a longitudinal direction of the respective filter bag and has a diameter that is substantially perpendicular to the longitudinal direction of the respective filter bag, wherein each of the one or more filter bags defines a continuous inner chamber that extends from the first end to the second end, and the diameter of each of the one or more filter bags changes along the longitudinal direction of the respective filter bag; and

wherein filter bag includes a first part, a second part, and a third part,

wherein

the first part extends from the inflow opening to a first point at a first distance along the longitudinal direction of each of the one or more filter bags, wherein the diameter of the filter bag along the first part is constant or approximately constant,

the second part extends from the first point along the longitudinal direction of each of the one or more filter bags to a second point at a second distance along the longitudinal direction of each of the one or more filter bags, wherein the diameter of the filter bag along the second part decreases, and

the third part extends from the second point along the longitudinal direction to a third point at a third distance along the longitudinal direction of each of the one or more filter bags, wherein the diameter of the filter bag along the third part increases, and

wherein the first part, the second part, and the third part are arranged along the continuous chamber between the first end and the second end.

2. A filter element according to claim 1 , wherein the inflow opening of the filter frame has a circular, polygonal or oval cross-section, whereby the cross-sections of each of the filter bag parallel to the inflow opening are also circular, polygonal or oval.

3. A filter element according to claim 1 , wherein the ratio of the maximum diameter to the length of each of the one or more filter bags is equal to one to at least three.

4. A filter element according to claim 1 , wherein the first distance along the longitudinal direction of each of the one or more filter bags, in which the diameter of each of the one or more filter bags from the inflow opening to the first point at the first distance is constant or approximately constant is equal to approximately 25% of the total length of the filter bag, wherein the second distance along the longitudinal direction of each of the one or more filter bags, in which the diameter then decreases, is approximately 60% of the total length of the filter bag, after which the diameter then increases again and the second end has the spherical or practically spherical form.

5. A filter element according to claim 1 , wherein the filter element comprises a plurality of filters that are connected together by the filter frame of each of the plurality of filters.

6. A filter element according to claim 1 , wherein the filter element comprises a plurality of filters that are affixed in a casing by the filter frame of each of the plurality of filters.

7. A filter element according to claim 1 , wherein the filter element comprises a plurality of filters that are connected together by the filter frame of each of the plurality of filters, or

wherein the filter element comprises a plurality of filters that are affixed in a casing by the filter frame of each of the plurality of filters, the filter frames of each of the plurality of filters and the casing forming one unit.

8. A filter element according to claim 1 , wherein the one or more filter bags and/or the filter frame for each filter can be detached and replaced separately.

9. A filter element according to claim 1 , wherein the filter frame and the one or more filter bags of each of the one or more filters form an inextricable unit.

10. A filter element according to claim 1 , wherein the one or more filter bags is made of paper, plastic, metal gauze, woven fabric, non-woven fabric, or a porous material.

11. A filter element according to claim 1 , wherein the one or more filter bags is made of a material that is rigid.

12. A filter element according to claim 1 , wherein each of the one or more filter bags is essentially cylindrical, each of the one or more filter bags having an essentially circular cross-section in a plane of the diameter.

13. A filter element according to claim 1 , wherein the first distance along the longitudinal direction of each of the one or more filter bags, in which the diameter of each of the one or more filter bags from the inflow opening to the first point at the first distance is constant or approximately constant is equal to approximately 25% of the total length of the filter bag.

14. A filter element according to claim 1 , wherein the second distance along the longitudinal direction of each of the one or more filter bags, in which the diameter then decreases, is approximately 60% of the total length of the filter bag.

15. A filter element according to claim 1 , wherein the ratio of the smallest diameter of the filter bag to the diameter of the filter bag at the inflow opening is equal to about 0.57.

16. A filter element according to claim 1 , wherein the ratio of the diameter of the second end to the diameter of the filter bag to the inflow opening is equal to about 0.71.

17. A filter element according to claim 1 , wherein the second end is rounded in a cross-section perpendicular to the longitudinal direction and the second end has a spherical or practically spherical form.