Piston seal

1. A ring seal for a reciprocating piston comprising a split ring with an outer circumferential surface defining a width of said split ring which forms a seal with a cylinder bore when installed in a seal groove associated with said piston and an inner circumferential surface, opposite said outer circumferential surface and facing said piston, said split ring comprising overlapping first and second end segments defining a split substantially flat surface there between, said split surface being transverse to the direction in which said piston moves when reciprocating within said cylinder bore and extending from said inner circumferential surface to said outer circumferential surface wherein said first end segment is associated with a leading lateral surface of said ring seal that faces a compression chamber associated with said piston, and said second end segment is associated with a trailing lateral surface of said ring seal that is opposite to said leading lateral surface, wherein spacing between said split surface and said leading lateral surface is approximately ⅔ of the width of said split ring, wherein said spacing between said split surface and said leading lateral surface reduces the risk of failure of said ring seal during operation.

2. The ring seal of claim 1 wherein said spacing between said split surface and said leading lateral surface reduces a risk of breakage of the ring seal due to stress exerted by a pressurized fluid on said ring seal during operation.

3. The ring seal of claim 1 wherein said first end segment has a length which reduces a risk of breakage of said ring seal due to stress exerted by a pressurized fluid on said ring seal during operation.

4. The ring seal of claim 1 wherein said split ring is made of a polymer composite.

5. The ring seal of claim 1 wherein said spacing between said split surface and said leading lateral surface and said spacing between said split surface and said trailing lateral surface are substantially constant along the circumferential direction of said seal.

6. The ring seal of claim 1 wherein said split surface extends in a direction perpendicular to said inner and outer circumferential surfaces of said ring seal.

7. A reciprocating pump for pumping a cryogenic fluid, the pump comprising a cylinder body having a cylinder bore and piston mounted in said cylinder bore and supported by said cylinder body, said piston being operable to move within said cylinder bore in a reciprocating motion such that it can compress the cryogenic fluid in a compression chamber of said cylinder bore, said piston further comprising a ring seal installed in a piston groove associated with said piston such that it seals said piston's surface against a wall of said cylinder bore, said ring seal comprising a split ring with an outer substantially flat circumferential surface facing said cylinder bore when said ring seal is installed in said piston groove and an inner circumferential surface, opposite said outer circumferential surface and facing said piston, said split ring comprising overlapping first and second end segments defining a split substantially flat surface there between, said split surface being transverse to the direction in which said piston moves when reciprocating within said cylinder bore and extending from said inner circumferential surface to said outer circumferential surface, wherein said first end segment is associated with a leading lateral surface of said ring seal that faces said compression chamber, the first segment subjected to a larger portion of stress exerted by the pressurized cryogenic fluid within the compression chamber compared to the stress exerted by the pressurized cryogenic fluid in the compression chamber on said second end segment, and said second end segment is associated with a trailing lateral surface of said ring seal that is opposite said first leading lateral surface, and wherein said split surface is spaced further from said leading lateral surface than it is spaced from said trailing lateral surface.

8. The reciprocating pump of claim 7 wherein said spacing between said split surface and said leading lateral surface reduces a risk of breakage of the ring seal due to the stress exerted by the pressurized cryogenic fluid on said ring seal during operation.

9. The reciprocating pump of claim 7 wherein said first end segment has a length which reduces a risk of breakage of said ring seal due to stress exerted by the pressurized cryogenic fluid during operation.

10. The reciprocating pump of claim 7 wherein said split surface extends in a direction perpendicular to said inner and outer circumferential surfaces of said ring seal.

11. The reciprocating pump of claim 7 wherein said ring seal is made of polymer.

12. The reciprocating pump of claim 7 wherein said ring seal is made of a polymer composite.

13. The reciprocating pump of claim 7 wherein said pump is designed to compress fluids to pressures higher than 3000 psi.

14. The ring seal of claim 1 wherein gaps B 1 and B 2 are provided between the surface of the first end segment and the surface of the second end segment to accommodate any contraction or expansion of the seal during operation.

15. The reciprocating pump of claim 7 wherein gaps B 1 and B 2 are provided between the surface of the first end segment and the surface of the second end segment to accommodate any contraction or expansion of the seal during operation.

16. The ring seal of claim 1 wherein said split ring is made of an ultrahigh molecular weight polyethylene.

17. The ring seal of claim 1 wherein said split ring is made of bronze filled poly tetrafluoroethylene.

18. The ring seal of claim 7 wherein said split ring is made of an ultrahigh molecular weight polyethylene.

19. The ring seal of claim 7 wherein said split ring is made of bronze filled poly tetrafluoroethylene.

20. A ring seal for a reciprocating piston of a cryogenic fluid pump, the ring seal comprising a polymer split ring with an outer circumferential surface defining a width of said split ring which forms a seal with a cylinder bore when installed in a seal groove associated with said piston and an inner circumferential surface, opposite said outer circumferential surface and facing said piston, said split ring comprising overlapping first and second end segments defining a split substantially flat surface there between, said split surface being transverse to the direction in which said piston moves when reciprocating within said cylinder bore and extending from said inner circumferential surface to said outer circumferential surface wherein said first end segment is associated with a leading lateral surface of said ring seal that faces a compression chamber associated with said piston, and said second end segment is associated with a trailing lateral surface of said ring seal that is opposite to said leading lateral surface, wherein said split surface is spaced further from said leading lateral surface than it is spaced from said trailing lateral surface to reduce the risk of breakage of said ring seal due to pressure exerted by a compressed fluid on said ring seal during operation.