Piston seal ring

1. A split ring seal comprising:

a first circumferential end and a second circumferential end;

an inner diameter surface and an outer diameter surface;

a first axial end face and a second axial end face;

a circumferentially distributed first plurality of open channels along the first axial end face; and

a circumferentially distributed second plurality of open channels along the second axial end face,

wherein:

the first circumferential end and the second circumferential end form a joint;

of the first plurality of open channels, two channels closest to diametrically opposite the joint are the largest in cross-sectional area; and

of the second plurality of open channels, two channels closest to diametrically opposite the joint are the largest in cross-sectional area.

2. The split ring seal of claim 1 wherein:

the first plurality of open channels and the second plurality of open channels are in registry.

3. The split ring seal of claim 1 wherein:

the first plurality of open channels and the second plurality of open channels have depth of 0.40 mm to 0.70 mm.

4. The split ring seal of claim 1 wherein:

a seal OD radii (R O ) is between 2.5 cm and 7.0 cm; and

on each of the first axial end face and the second axial end face a total cross-sectional area of the channels is k*R O where k is a constant of value in a range of 0.012 cm 2 /cm to 0.020 cm 2 /cm.

5. The split ring seal of claim 1 comprising:

a metallic substrate.

6. The split ring seal of claim 1 wherein:

of the first plurality of open channels, the two channels closest to diametrically opposite the joint are separated by a larger gap from each other than from the next respective adjacent channels; and

of the second plurality of open channels, the two channels closest to diametrically opposite the joint are separated by a larger gap from each other than from the next respective adjacent channels.

7. The split ring seal of claim 1 wherein:

of the first plurality of open channels, the two channels closest to diametrically opposite the joint are 20% to 100% larger in cross-sectional area than the next respective adjacent channels; and

of the second plurality of open channels, two channels closest to diametrically opposite the joint are 30% to 100% larger in cross-sectional area than the next respective adjacent channels.

8. The split ring seal of claim 1 wherein:

each of the first and second pluralities of open channels comprise at least six open channels.

9. The split ring seal of claim 1 wherein:

the first circumferential end and the second circumferential end form a shiplap joint.

10. The split ring seal of claim 1 comprising:

a metallic substrate; and

an outer diameter coating including at least an aluminum bronze layer.

11. The split ring seal of claim 10 wherein:

the split ring seal comprises an axial end face coating comprising molybdenum disulfide as a solid lubricant; and

the outer diameter coating includes molybdenum disulfide as a solid lubricant atop the aluminum bronze layer.

12. A machine including the split ring seal of claim 1 and further comprising:

an inner member;

an outer member encircling the inner member; and

a groove in one of the inner member and the outer member, the split ring seal accommodated in the groove and contacting a surface of the other of the inner member and the outer member.

13. The machine of claim 12 being a gas turbine engine wherein:

the groove is in the inner member;

the inner member is a shaft of a spool; and

the outer member is a seal runner protruding from a bore of a disk of a rotor stack of the spool.

14. The machine of claim 12 wherein:

the inner member is made of a nickel-based alloy;

the outer member is made of a nickel-based alloy; and

the split ring seal comprises or consists of a nickel-based alloy or a cobalt-based alloy.

15. A method for using the machine of claim 12 , the method comprising:

driving rotation of the inner member and the outer member and creating a pressure difference across the split ring seal; and

the pressure difference causing gas flow through the distributed plurality of open channels, the gas flow reducing a circumferential thermal asymmetry induced by a circumferentially asymmetrical seating of at least one of the first axial end face and the second axial end face.

16. An apparatus comprising:

an inner member;

an outer member encircling the inner member; and

a split ring seal accommodated in a groove in one of the inner member and the outer member and contacting a surface of the other of the inner member and the outer member,

wherein:

the split ring seal comprises:

a first circumferential end and a second circumferential end;

an inner diameter surface and an outer diameter surface; and

a first axial end face and a second axial end face;

the first circumferential end and the second circumferential end form a joint;

the split ring seal comprises venting means for bypassing the seal so as to compensate for an asymmetry of flow due to leakage through the joint.

17. The apparatus of claim 16 wherein:

the means comprises a circumferentially distributed plurality of open channels in the first axial end face; and

of the plurality of open channels, two channels closest to diametrically opposite the joint are the largest in cross-sectional area.

18. The apparatus of claim 17 wherein:

of the plurality of open channels, the two channels closest to diametrically opposite the joint are separated by a larger gap from each other than from the next respective adjacent channels.

19. The apparatus of claim 17 wherein:

of the plurality of open channels, the two channels closest to diametrically opposite the joint are 20% to 100% larger in cross-sectional area than the next respective adjacent channels.

20. The apparatus of claim 16 wherein:

the groove is in the inner member; and

the sealing surface is an inner diameter surface of the outer member.