Mechanical override

1. A valve system comprising:

a closure member that is linearly translatable within a valve body;

a fail safe assembly comprising:

a hollow body having a first end that is connected to the valve body,

a spring disposed within said hollow body between the first end and a piston disposed within the hollow body, wherein the spring biases the piston toward the second end of the hollow body, and

a first rod member that is connected to said closure member and the piston;

a linear actuator engaged with a second end of the hollow body of said fail safe assembly, wherein said linear actuator is operable to move the first rod member; and

a mechanical override system connecting said linear actuator to said fail safe assembly, wherein said mechanical override system is operable to move the linear actuator relative to the valve body.

2. The valve system of claim 1 wherein said linear actuator comprises a second rod member that is operable to move the first rod member.

3. The valve system of claim 2 wherein said fail safe assembly is operable to translate said closure member independent of operation of said linear actuator.

4. The valve system of claim 2 wherein said valve system has a first mode, wherein the second rod member extends from said linear actuator so as to move said closure member within the valve body, and a second mode, wherein said linear actuator is moved relative so said valve body so as to move said closure member within the valve body.

5. The valve system of claim 1 wherein said mechanical override system comprises a gear system operable to translate said linear actuator relative to the valve body.

6. The valve system of claim 1 wherein said spring partially surrounds the piston and said linear actuator.

7. The valve system of claim 1 wherein said linear actuator is an electric actuator.

8. The valve system of claim 1 further comprising an ROV interface operable to actuate said mechanical override system.

9. A valve actuation system comprising:

a hollow body having a first end coupled to a valve body;

a linear actuator partially disposed within a second end of said hollow body; and

a mechanical override system connected to said hollow body and said linear actuator and operable to move said linear actuator relative to the valve body.

10. The valve actuation system of claim 9 further comprising:

a piston at least partially disposed within said hollow body; and

a first rod member connected between said piston and a closure member disposed within the valve body.

11. The valve actuation system of claim 10 further comprising a spring disposed between said piston and said hollow member, wherein said spring biases said piston toward the second end of said hollow body.

12. The valve actuation system of claim 11 wherein said mechanical override system comprises a gear system operable to translate said linear actuator relative to said hollow body.

13. The valve actuation system of claim 10 wherein said linear actuator comprises a second rod member.

14. The valve actuation system of claim 13 wherein said linear actuator has a first mode wherein the second rod member extends from said linear actuator so as to move said piston toward the first end of said hollow body while said linear actuator does not move relative to said valve body.

15. The valve actuation system of claim 14 wherein said linear actuator has a second mode wherein said linear actuator moves relative to said valve body so as to move said piston toward the first end of said hollow body.

16. The valve actuation system of claim 9 further comprising an interface for coupling an ROV to said mechanical override system.

17. A valve system comprising:

a closure member disposed within a valve body;

a hollow body having a first end that is connected to the valve body;

a spring disposed within said hollow body between the first end and a piston disposed within the hollow body, wherein the spring biases the piston toward the second end of the hollow body;

a first rod member connected to said closure member and the piston;

a linear actuator at least disposed within the second end of the hollow body and having a second rod member extendable to translate said closure member within the valve body; and

means for moving said linear actuator relative to the valve body so as to translate said closure member without extending the second rod member from said linear actuator.

18. The valve system of claim 17 wherein said means for moving said linear actuator connects said linear actuator to the valve body.

19. The valve system of claim 17 wherein said means for moving said linear actuator comprises an ROV interface.