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Apparatus and methods for operating a valve assembly for a dual chamber orifice fitting. The dual chamber orifice fitting comprises a body attached to a top. A passageway connects between the body and the top and allows an orifice plate carrier to move between the body and the top. A valve assembly

Apparatus and methods for operating a valve assembly for a dual chamber orifice fitting. The dual chamber orifice fitting comprises a body attached to a top. A passageway connects between the body and the top and allows an orifice plate carrier to move between the body and the top. A valve assembly selectably closes the passageway. Embodiments of the valve assembly comprise a seat, a plug, and a stem. The valve assembly has a closed position, wherein a curved outer surface of the plug sealingly engages a curved sealing surface of the seat and prohibits fluid communication through the passageway. The valve assembly has an open position, wherein a plug aperture is aligned with a seat aperture to allow the orifice plate carrier to move through the passageway.

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What is claimed is: 1. A valve assembly for a dual chamber orifice fitting comprising: an orifice plate carrier; a seat having a seat aperture; a plug having a plug aperture and curved outer surface, wherein said plug has a closed position prohibiting fluid communication across said plug, an open p

What is claimed is: 1. A valve assembly for a dual chamber orifice fitting comprising: an orifice plate carrier; a seat having a seat aperture; a plug having a plug aperture and curved outer surface, wherein said plug has a closed position prohibiting fluid communication across said plug, an open position, wherein the plug aperture is aligned with the seat aperture, so that said orifice plate carrier is movable through the plug aperture between an upper and lower chamber of the dual chamber orifice fining, and an equalized position, wherein the plug aperture is not aligned with the seat aperture and fluid communication is permitted across said plug between an upper and lower chamber of the dual chamber orifice fitting; and a stem coupled to an end of said plug and adapted to rotate said plug between the closed position and the open position. 2. The valve assembly of claim 1 wherein in the closed position said plug is adapted to move relative to said stem. 3. The valve assembly of claim 2 further comprising a slot on an end of said plug, wherein said slot is arranged perpendicular to the plug aperture and is engaged with said stem. 4. The valve assembly of claim 1 further comprising one or more equalizer ports connecting said plug aperture to the curved outer surface of said plug, wherein in the equalized position where fluid communication across said plug is permitted through said one or more equalizer ports. 5. The valve assembly of claim 1 further comprising a bonnet connected to the dual chamber orifice fitting, wherein said bonnet is operable to support said stem. 6. The valve assembly of claim 5 further comprising: a circumferential groove on said stem; and a pin moveably connected to said bonnet, wherein said pin is operable to engage said groove. 7. The valve assembly of claim 6 wherein said pin engages said groove in the closed and equalized positions but does not engage said groove in the open position. 8. The valve assembly of claim 1 further comprising a saddle adapted to engage said plug in a position opposite said seat. 9. The valve assembly of claim 8 wherein said saddle biases said plug against said seat. 10. The valve assembly of claim 1 wherein said plug is rotated approximately 15 degrees between the closed position and the equalized position. 11. The valve assembly of claim 1 wherein said plug is rotated approximately 90 degrees between the closed position and the open position. 12. A dual chamber orifice fitting comprising: a body having a lower chamber in fluid communication with a pipeline; a top attached to said body, wherein said top has an upper chamber; a passageway between the upper and lower chambers; an orifice plate carrier moveably disposable through said passageway between the upper chamber and the lower chamber; a valve seat having a seat aperture therethrough, wherein the seat aperture is substantially aligned with said passageway; a rotatable plug having a plug aperture therethrough, said rotatable plug having a cylindrical outer surface operable to sealingly engage said valve seat when said rotatable plug is in a closed position; and a stem connected to said plug and operable to rotate said plug from the closed position to an open position wherein the plug aperture is aligned with the seat aperture and the passageway so that said plate carrier is movable through the plug aperture between the upper and lower chambers. 13. The dual chamber orifice fining of claim 12 wherein the orifice plate carrier can move through said passageway when said rotatable plug is in the open position. 14. The dual chamber orifice fitting of claim 12 further comprising one or more equalizer ports through said rotatable plug at an angle to the plug aperture, wherein said rotatable plug has an equalized position wherein the plug aperture is not aligned with the seat aperture and fluid communication through said passageway is permitted through said equalizer port. 15. The valve assembly of claim 14 wherein said rotatable plug is rotated approximately 15 degrees between the closed position and the equalized position. 16. The valve assembly of claim 12 wherein said rotatable plug is rotated approximately 90 degrees between the closed position and the open position. 17. The dual chamber orifice fining of claim 12 further comprising a bonnet connected to said body and operable to support said stem. 18. The dual chamber orifice fitting of claim 17 further comprising: a circumferential groove on said stem; and a pin moveably connected to said bonnet, wherein said pin is operable to engage said groove. 19. The dual chamber orifice fitting of claim 18 wherein said pin engages said groove in the closed and equalized positions but does not engage said groove in the open position. 20. The dual chamber orifice fitting of claim 12 further comprising a saddle supported by said body and having a curved surface operable to engage a portion of the cylindrical outer surface of said rotatable plug opposite said valve seat. 21. The dual chamber orifice fitting of claim 20 wherein said saddle biases said rotatable plug against said valve seat. 22. The dual chamber orifice fitting of claim 21 further comprising a spring disposed between said body and said saddle, wherein said spring is operable to bias said plug against said seat. 23. A method for operating a dual chamber orifice fitting, the method comprising: rotating a valve assembly from a first position isolating a first chamber of the fitting from a second chamber of the fitting to a second position to expose a first aperture allowing fluid communication between the chambers; allowing fluid flow between the chambers; rotating the valve assembly to an third position to place a second aperture in fluid communication with the first and second chambers; actuating a drive mechanism to move an orifice plate carrier between the chambers by passing though the second aperture; and rotating the valve assembly back to the first position. 24. The method of claim 23 further comprising maintaining the second position until pressure is equal in the first and second chambers. 25. The method of claim 23 wherein the valve assembly comprises: a valve seat attached to the fitting; a plug adapted to engage the valve seat; a stem adapted to rotate the plug, wherein the plug is adapted to move relative to the stem; and a bonnet attached to the fitting and supporting the stem. 26. The method of claim 25 wherein a pin attached to the bonnet engages a slot on the stem as the valve assembly is moved from the first position to the second position. 27. The method of claim 26 further comprising removing the pin from the slot before rotating the valve assembly to the third position.