Seal assembly for a valve stem

1. A seal assembly for a valve stem, comprising:

an external seal placed on a valve stem facing an external environment;

an internal seal placed on said valve stem facing a process environment; said external and internal seals defining, in cooperation with each other, a chamber for the containment of barrier fluid; said chamber having an inlet configured to be placed into fluid communication with a source of barrier fluid;

a detector connected between the inlet of the chamber and the process environment, the detector detecting an amount of the barrier fluid inside said chamber; and

a pressurizer device configured to provide said chamber with a positive pressure with respect to said process environment,

wherein the pressurizer device comprises a piston at least partially defining said chamber, said piston having a process surface contacting the process environment and an internal surface contacting the barrier fluid, and

wherein the detector detects the amount of the barrier fluid inside the chamber by detecting a pressure difference between the process surface and the internal surface of the piston.

2. The seal assembly according to claim 1 , wherein said internal seal comprises a first internal seal placed between said piston and said valve stem.

3. The seal assembly according to claim 1 , wherein said pressurizer device comprises a spring acting on said piston and configured to provide a force on said piston which adds to the process pressure.

4. The seal assembly according to claim 3 , wherein said force is applied on the internal surface of said piston.

5. The seal assembly according to claim 3 , wherein the spring is configured to be extended by the inflow of barrier fluid inside said chamber.

6. The seal assembly of claim 1 , wherein the pressurizer device is installed coaxially with said valve stem.

7. A valve comprising:

a seat;

a valve stem inserted into said seat; and

a seal assembly comprising:

an external seal placed on the valve stem facing an external environment;

an internal seal placed on said valve stem facing a process environment; said external and internal seals defining, in cooperation with each other, a chamber for the containment of barrier fluid; said chamber having an inlet configured to be placed into fluid communication with a source of barrier fluid;

a detector connected between the inlet of the chamber and the process environment, the detector detecting an amount of the barrier fluid inside said; and

a pressurizer device configured to provide said chamber with a positive pressure with respect to said process environment;

wherein said seal assembly is installed onto said valve stem,

wherein the pressurizer device comprises a piston at least partially defining said chamber, said piston having a process surface contacting the process environment and an internal surface contacting the barrier fluid, and

wherein the detector detects the amount of the barrier fluid inside the chamber by detecting a pressure difference between the process surface and the internal surface of the piston.

8. The seal assembly according to claim 2 , wherein said pressurizer device comprises a spring acting on said piston and configured to provide a force on said piston which adds to the process pressure.

9. The seal assembly according to claim 4 , wherein the spring is configured to be extended by the inflow of barrier fluid inside said chamber.

10. The valve of claim 7 , wherein the pressurizer device is installed coaxially with said valve stem.

11. The valve according to claim 7 , wherein said internal seal comprises a first internal seal placed between said piston and said valve stem.

12. The valve according to claim 7 , wherein said pressurizer device comprises a spring acting on said piston and configured to provide a force on said piston which adds to the process pressure.

13. The valve according to claim 12 , wherein said force is applied on the internal surface of said piston.

14. The valve according to claim 12 , wherein the spring is configured to be extended by the inflow of barrier fluid inside said chamber.

15. The valve according to claim 11 , wherein said pressurizer device comprises a spring acting on said piston and configured to provide a force on said piston which adds to the process pressure.

16. The valve according to claim 15 , wherein the spring is configured to be extended by the inflow of barrier fluid inside said chamber.