Stirling cycle machine

1. A rod seal assembly comprising:

a housing between a first space and a second space, the housing including a passage connecting the first space and the second space, the passage defining an axis;

a reciprocating rod disposed in the passage, the reciprocating rod extending into the first space and the second space;

a floating bushing able to move axially and radially relative to the passage axis within the housing, the floating bushing disposed coaxially around the reciprocating rod;

a rod seal sealing the outside diameter of the reciprocating rod relative to an inside surface of the floating bushing; and

a first stationary bushing fixed within the housing; and

a second stationary bushing fixed within the housing, the second stationary bushing axially aligned to the first stationary bushing and defining an annular space between the first and second stationary bushings, wherein the floating bushing extends into the annular space and forms a seal with one of the first and second stationary bushings to an axial flow of fluid in the presence of a pressure difference between the first space and the second space.

2. The rod seal assembly of claim 1 , wherein the floating bushing is configured to move radially to center on the reciprocating rod when the pressure difference between the first and second space is small and form the seal with the stationary bushing when the pressure difference is larger.

3. The rod seal assembly of claim 1 , wherein the rod seal is a spring energized seal.

4. The rod seal assembly of claim 1 , wherein the floating bushing further comprises a circumferential flange on the outside surface of the floating bushing that is configured to extend into the annular space and form a seal with one of the stationary bushings.

5. The rod seal assembly of claim 1 , wherein the rod seal is formed of a PTFE composite.

6. The rod seal assembly of claim 1 , wherein the floating bushing and the first stationary bushing are formed of a wear resistance metal.

7. A rod seal assembly of claim 1 , further comprising:

a scraper ring disposed coaxially around the reciprocating rod and disposed within the housing between the floating bushing and the first space; and

a passageway connecting the first space to an annular gap disposed around the reciprocating rod between the scraper ring and the floating bushing.

8. A rod seal assembly of claim 7 , further comprising a magnetic particle trap disposed between the scraper ring and floating bushing.

9. A rod seal assembly comprising:

a housing between a first space and a second space, the first space and second space having a pressure difference, the housing including a passage connecting the first space and the second space, the passage defining an axis;

a reciprocating rod disposed in the passage, the rod extending into the first space and the second space;

a floating clearance bushing configured to move axially and radially relative to the passage within the housing and disposed coaxially around the reciprocating rod and forms a clearance seal with the reciprocating rod;

a first stationary annular element fixed within the housing;

a second stationary annular element fixed in housing; and

the floating clearance bushing configured to form a face seal with only one of the first and second stationary annular elements.

10. The rod seal assembly of claim 9 , wherein the floating clearance bushing is configured to move radially to center on the reciprocating rod when the pressure difference is small and form the face seal with the stationary annular element when the pressure difference is larger.

11. A rod seal assembly of claim 9 , further comprising a spring energized face seal on at least one end of the floating clearance bushing.

12. A rod seal assembly of claim 9 , further comprising:

a second floating clearance bushing disposed around the reciprocating rod; and

two spring energized lip seals disposed around the reciprocating rod and axially located within or between the two floating clearance bushings.

13. A rod seal assembly of claim 9 , further comprising:

a scraper ring disposed coaxially around the reciprocating rod and disposed within the housing between the floating clearance bushing and the first space; and

a passage connecting the first space to an annular gap disposed around the reciprocating rod between the scraper ring and the floating clearance bushing.

14. A rod seal assembly of claim 9 , further comprising a magnetic particle trap disposed between the scraper ring and floating clearance bushing.

15. A rod seal assembly of claim 9 wherein the first stationary bushing forms an axial seal with the floating bushing at least part of the time the pressure difference across the rod seal assembly is in a first direction.

16. A rod seal assembly of claim 15 further comprising a second stationary bushing configured to form an axial seal with the floating bushing at least part of the time the pressure difference across the reciprocating rod seal unit is in a second direction.

17. A rod seal assembly comprising: a housing between a first space and a second space, the first space and second space having a pressure difference between them, the housing including a passage connecting the first space and the second space, the passage defining an axis;

a reciprocating rod disposed in the passage, the reciprocating rod extending into the first space and the second space;

a floating bushing able to move axially and radially relative to the passage axis within the housing, the floating bushing-disposed coaxially around the reciprocating rod;

a rod seal sealing the outside diameter of the reciprocating rod relative to an inside surface of the floating bushing; and

a first stationary bushing fixed within the housing, the first stationary bushing configured to form an axial seal with the floating bushing at least part of the time the pressure difference is in a first direction; and

a second stationary bushing fixed within the housing, the second stationary bushing configured to form an axial seal with the floating bushing at least part of the time the pressure difference is in a second direction.

18. A rod seal assembly comprising:

a housing between a first space and a second space, the first space and second space having a pressure difference between them, the housing including a passage connecting the first space and the second space, the passage defining an axis;

a reciprocating rod disposed in the passage, the reciprocating rod extending into the first space and the second space;

a floating bushing able to move axially and radially relative to the passage axis within the housing, the floating bushing disposed coaxially around the reciprocating rod;

a rod seal sealing the outside diameter of the reciprocating rod relative to an inside surface of the floating bushing;

a first stationary bushing fixed within the housing, the first stationary bushing forming a seal with the floating bushing to an axial flow of fluid in the presence at least part of the time the pressure difference between the first space and the second space is in a first direction;

a second stationary bushing fixed within the housing, the second stationary bushing configured to form an axial seal with the floating bushing at least part of the time the pressure difference is in a second direction;

a scraper ring disposed coaxially around the reciprocating rod and disposed within the housing between the floating bushing and the first space; and

a magnetic particle trap disposed between the scraper ring and floating bushing.

19. A rod seal assembly comprising:

a housing between a first space and a second space, the first space and second space having a pressure difference, the housing including a passage connecting the first space and the second space, the passage defining an axis;

a reciprocating rod disposed in the passage, the reciprocating rod extending into the first space and the second space;

a floating clearance bushing configured to move axially and radially relative to the passage within the housing and disposed coaxially around the reciprocating rod and forms a clearance seal with the reciprocating rod;

a first stationary annular element fixed within the housing, the first stationary annular element configured to form a face seal with the floating clearance bushing at least part of the time the pressure difference is in a first direction;

a second stationary bushing fixed within the housing, the second stationary bushing configured to form an axial seal with the floating bushing at least part of the time the pressure difference is in a second direction;

a scraper ring disposed coaxially around the reciprocating rod and disposed within the housing between the floating bushing and the first space; and

a magnetic particle trap disposed between the scraper ring and floating clearance bushing.