Isolation valve with debris control and flow tube protection

1. An isolation valve for use as part of a casing string, the isolation valve comprising:

a housing having a bore, a valve cavity, and a seat;

a flapper movable between a first position in which the flapper obstructs the housing bore by engaging the seat and a second position in which the flapper is disposed in the valve cavity;

a flow tube configured to allow movement of the flapper between the first and second positions; and

a hinge arrangement having a first portion connected to the flapper, a second portion directly fastened to the housing by one or more connection members with freedom for a small alignment movement, and

an adjustment locking connection member directly attached to the housing by a thread connection and configured to lock the second portion to the housing after the alignment movement.

2. The isolation valve of claim 1 , wherein the adjustment locking connection member is locked by tightening the thread connection along a plane of a mating surface between the second portion and the housing.

3. The isolation valve of claim 1 , further comprising a safety member operable to prevent loss of the adjustment locking connection member.

4. The isolation valve of claim 3 , wherein the safety member is a screw.

5. The isolation valve of claim 1 , further comprising a piston coupled to the flow tube.

6. The isolation valve of claim 5 , wherein the piston is configured to move the flow tube within the housing when fluid pressure acts on the piston.

7. The isolation valve of claim 5 , further comprising an engagement assembly attached to the housing by a shearable member,

wherein the piston is configured to move the flow tube into engagement with the engagement assembly to substantially prevent debris from entering the valve cavity when the flapper is in the second position.

8. The isolation valve of claim 1 , wherein the adjustment locking connection member prevents an axial movement of the second portion of the hinge arrangement along a plane of a mating surface between the hinge arrangement and the housing.

9. An isolation valve comprising:

a housing having a bore;

a seat connected to the housing;

a flapper pivotally movable between a closed position in which the bore is blocked by engagement of the flapper with the seat and an open position in which the bore is open to fluid flow;

a hinge directly connected to the seat by one or more connection members, wherein the hinge connects the flapper to the seat with freedom for a small alignment movement to ensure proper engagement of the flapper with the seat;

an adjustment locking connection member directly attached to the seat by a thread connection and configured to lock the hinge to the seat after the alignment movement; and

a flow tube for shifting the flapper between the open position and the closed position.

10. The isolation valve of claim 9 , wherein the adjustment locking connection member is locked by tightening the thread connection along a plane of a mating surface between the hinge and the seat.

11. The isolation valve of claim 9 , further comprising a safety member operable to prevent loss of the adjustment locking connection member.

12. The isolation valve of claim 11 , wherein the safety member is a screw.

13. The isolation valve of claim 9 , further comprising a piston coupled to the flow tube.

14. The isolation valve of claim 13 , wherein the piston is configured to move the flow tube within the housing when fluid pressure acts on the piston.

15. The isolation valve of claim 13 , wherein:

the housing further has a valve cavity for receiving the flapper in the open position, and

the isolation valve further comprises an engagement assembly attached to the housing by a shearable member, and

the piston is configured to move the flow tube into engagement with the engagement assembly to substantially prevent debris from entering the valve cavity when the flapper is in the open position.

16. The isolation valve of claim 13 , wherein the adjustment locking connection member prevents an axial movement of the hinge along a plane of a mating surface between the hinge and the seat.

17. An isolation valve, comprising:

a flapper;

a housing having a bore, a seat to engage the flapper and close the bore, and a flapper cavity for receiving the flapper; and

a hinge arrangement movably connecting the flapper to the housing, wherein the flapper is movable between the flapper cavity and the seat, and the hinge arrangement includes:

a first portion connected to the flapper,

a second portion directly connected to the housing by one or more connection members with freedom for a small alignment movement; and

an adjustment locking connection member directly attached to the housing by a thread connection, wherein the adjustment locking connection member is positioned to prevent an axial movement of the second portion along a plane of a mating surface between the second portion and the housing.

18. The isolation valve of claim 17 , further comprising a safety member disposed adjacent the adjustment locking connection member.

19. The isolation valve of claim 18 , wherein the safety member is a screw, a snap ring, or a pin.

20. The isolation valve of claim 17 , wherein the one or more connection members are screws.