Filter cartridge

1. A filter cartridge comprising:

a sump;

an inlet/outlet portion extending from one end of the sump having an outside diameter that is smaller than an outside diameter of the sump, the inlet/outlet portion having a cartridge inlet port and a cartridge outlet port;

a first lug on the inlet/outlet portion protruding outwardly from a surface of the inlet/outlet portion in a radial direction perpendicular to a central axis of the filter cartridge;

a shoulder surface that is formed by the intersection of the sump and the inlet/outlet portion;

a filter disposed within the sump; and

the first lug comprising a curved surface facing the shoulder surface and curving away from the shoulder surface such that a distance between the curved surface and the shoulder surface varies and wherein a minimum distance between the curved surface and the shoulder surface is located in a plane intersecting with the central axis and bisecting the first lug into two halves.

2. The filter cartridge of claim 1 wherein the curved surface comprises a half-moon shape.

3. The filter cartridge of claim 1 further comprising a mechanical keying system on the inlet/outlet portion.

4. The filter cartridge of claim 3 wherein the mechanical keying system comprises protrusions and depressions on the inlet/outlet portion.

5. The filter cartridge of claim 1 wherein the inlet/outlet portion further comprises one or more protrusions that protrude outwardly in a radial direction perpendicular to the central axis.

6. The filter cartridge of claim 5 wherein the one or more protrusions are complementary to one or more depressions on a manifold.

7. The filter cartridge of claim 1 wherein a slope of the curved surface transitions from a positive slope to a negative slope at the minimum distance.

8. The filter cartridge of claim 7 wherein the curved surface is symmetrical about the minimum distance.

9. A filter cartridge comprising:

a sump;

a stepped inlet/outlet having a first portion extending from one end of the sump having an outside diameter that is smaller than an outside diameter of the sump, and having a second portion extending from the first portion having an outside diameter that is smaller than the outside diameter of the first portion, the stepped inlet/outlet comprising a cartridge inlet port in the first portion, and a cartridge outlet port in the second portion aligned with a central axis of the filter cartridge;

a first lug on the first portion protruding outwardly from a surface of the first portion in a radial direction perpendicular to the central axis;

a shoulder surface that is formed by the intersection of the sump and the stepped inlet/outlet;

a filter disposed within the sump; and

the first lug comprising a curved surface facing the shoulder surface and curving away from the shoulder surface such that a distance between the curved surface and the shoulder surface varies and wherein a minimum distance between the curved surface and the shoulder surface is located in a plane intersecting with the central axis and bisecting the first lug into two halves.

10. The filter cartridge of claim 9 further comprising a mechanical keying system on the stepped inlet/outlet.

11. The filter cartridge of claim 10 wherein the mechanical keying system comprises protrusions and depressions on the stepped inlet/outlet.

12. The filter cartridge of claim 9 wherein the stepped inlet/outlet further comprises one or more protrusions that protrude outwardly in a radial direction perpendicular to the central axis.

13. The filter cartridge of claim 12 wherein the one or more protrusions are complementary to one or more depressions on a manifold.

14. The filter cartridge of claim 9 wherein a slope of the curved surface transitions from a positive slope to a negative slope at the minimum distance.

15. The filter cartridge of claim 14 wherein the curved surface is symmetrical about the minimum distance.

16. A filter cartridge comprising:

a sump;

a stepped inlet/outlet having a first portion extending from one end of the sump having an outside diameter that is smaller than an outside diameter of the sump, and having a second portion extending from the first portion having an outside diameter that is smaller than the outside diameter of the first portion, the stepped inlet/outlet comprising a cartridge inlet port and a cartridge outlet port aligned with a central axis of the filter cartridge;

a first lug on the first portion protruding outwardly from a surface of the first portion in a radial direction from the central axis of the filter cartridge;

a second lug on the first portion protruding outwardly from the surface of the first portion in a radial direction from the central axis of the filter cartridge;

a shoulder surface that is formed by the intersection of the sump and the stepped inlet/outlet;

a filter disposed within the sump; and

a first curved surface on the first lug facing the shoulder surface and curving away from the shoulder surface such that a distance between the first curved surface and the shoulder surface varies and wherein a minimum distance between the first curved surface and the shoulder surface is located in a plane intersecting with the central axis and bisecting the first lug into two halves; and

a second curved surface on the second lug facing the shoulder surface and curving away from the shoulder surface such that a distance between the second curved surface and the shoulder surface varies and wherein a minimum distance between the second curved surface and the shoulder surface is located in the plane intersecting with the central axis and bisecting the first lug into two halves.

17. The filter cartridge of claim 16 further comprising a mechanical keying system on the stepped inlet/outlet.

18. The filter cartridge of claim 17 wherein the mechanical keying system comprises protrusions and depressions on the stepped inlet/outlet.

19. The filter cartridge of claim 16 wherein the stepped inlet/outlet further comprises one or more protrusions that protrude outwardly in a radial direction perpendicular to the central axis.

20. The filter cartridge of claim 19 wherein the one or more protrusions are complementary to one or more depressions on a spool valve manifold.

21. The filter cartridge of claim 16 wherein a slope of the first curved surface transitions from a positive slope to a negative slope at the minimum distance and wherein a slope of the second curved surface transitions from a positive slope to a negative slope at the minimum distance.