Two-part back cap for a plug valve and plug valves incorporating same

1. A two-part back cap for a plug valve having a plug value body, comprising:

a back cap seal body having an inner end and an outer end, the inner end comprising a seal rim with an O-ring groove that supports an O-ring seal between the seal rim and the plug valve body, and the outer end comprising first and second surfaces respectively inclined towards the seal rim at different angles; and

a back cap retainer nut that threadedly engages the plug valve body to retain the back cap seal body within the plug valve body, the back cap retainer nut supporting only the first surface unless the plug valve is subjected to high fluid pressures.

2. The two-part back cap as claimed in claim 1 wherein the first surface is inclined toward the seal rim at 20°-40° with respect to a plane perpendicular to a central axis of the back cap seal body.

3. The two-part back cap as claimed in claim 1 wherein the second surface is inclined toward the seal rim at 0.5°-1.5° more than the first surface.

4. The two-part back cap as clamed in claim 2 wherein the first surface is inclined towards the seal rim at about 30°.

5. The two-part back cap as claimed in claim 4 wherein the second surface is inclined toward the seal rim at about 30.5°.

6. The two-part back cap as claimed in claim 1 wherein the back cap seal body further comprises a plug support surface for supporting a valve plug in the plug valve body.

7. The two-part back cap as claimed in claim 6 wherein the back cap seal body further comprises a radius undercut adjacent the plug support surface.

8. The two-part back cap as claimed in claim 7 wherein a transition from the first surface the second surface is axially aligned with an inner edge of the radius.

9. The two-part back cap as claimed in claim 1 wherein the back cap seal body further comprises at least two tapped bores to which a puller is connected to remove the back cap seal body from the plug valve body.

10. The two-part back cap as claimed in claim 1 wherein the seal rim comprises a second O-ring groove.

11. A plug valve, comprising:

a back cap seal body having an inner end with a plug support surface for supporting a plug received in a plug valve body of the plug valve and an outer end comprising first and second surfaces inclined at different angles; and

a back cap retainer nut with an inner end that supports only the first surface unless the plug valve is subjected to high fluid pressure, and threads that engage the plug valve body to retain the plug and the back cap seal body within the plug valve body.

12. The plug valve as claimed in claim 11 wherein the back cap seal body comprises a seal rim along an outer edge of the inner end, an outer periphery of the seal rim comprising at least one O-ring groove.

13. The plug valve as claimed in claim 12 wherein the back cap seal body further comprises a radius undercut adjacent the plug support surface.

14. The plug valve as claimed in claim 13 wherein the first surface is inclined toward the seal rim at a first angle, and the second surface is inclined toward the seal rim at a second angle greater than the first angle.

15. The plug valve as claimed in claim 14 wherein the second surface commences in axial alignment with an inner edge of the radius.

16. A two-part back cap for a plug valve body, comprising:

a back cap seal body comprising an inner end with a plug support surface that supports a valve plug in the plug valve body, a seal rim that supports at least one O-ring against an end cap seal surface of the plug valve body, and an outer end having a first surface adjacent a stud bore through the back cap seal body and a second surface continuous with the first surface, the first surface being inclined toward the seal rim at a first angle and the second surface being inclined toward the seal rim at a second angle that is greater than the first angle; and

a back cap retainer nut that supports the back cap seal body and has an inner end inclined toward the seal rim at the first angle, and further having a thread for engaging the plug valve body to retain the back cap seal body and the valve plug within the plug valve body.

17. The plug valve as claimed in claim 16 further comprising a radius undercut adjacent the plug support surface.

18. The plug valve as claimed in claim 17 wherein the second surface commences in axial alignment with an inner edge of the radius.

19. The plug valve as claimed in claim 18 wherein the second surface is inclined toward the seal rim at 1°-1.5° more than the first surface.