Radially compliant - zero net thermal radial taper mechanical face seal

#This invention relates to a new mechanical face seal design which improves the performance characteristics of the seal. A mechanical face seal is a device which controls fluid leakage between two regions under different pressures while allowing a rotating shaft to pass between the regions. Such seals are widely used in ships, submarines, process pumps, and compressors.

#Conventional mechanical face seals will often leak and sometimes have short lives because the geometry between the seal faces deviates from parallel due to various thermal- and pressure-caused distortions of the seal. Mechanical seals are generally known as troublesome devices because it is most often the failure of a seal which necessitates the rebuilding of a pump. Mechanical seals, in general, have only a fraction of the life of bearings. Seals having longer life with low leakage and reliable performance would serve to upgrade the performance of mechanical equipment and reduce the cost of operation. Conventional seals usually have high thermal distortion, and they are so rigid (low radial compliance) that the faces cannot deflect back to the desired parallel condition.

#Attempts have been made in the prior art to achieve radial compliance, but these attempts have not been entirely successful. U.S. Pat. No. 4,212,475, entitled SELF ALIGNING SPIRAL GROOVE FACE, to Sedy; Sedy, Josef, "Improved Performance of Film-Riding Gas Seals Through Enhancement of Hydrodynamic Effects," ASLE Preprint No. 78-LC-3B-1, October, 1978; and Sedy, Josef, "A New Self-Aligning Mechanism for the Spiral-Groove Gas Seal Stability " ASLE Preprint No. 79-LC-3B-3, October, 1979; all disclose the use of a low Young's modulus material ring to enhance compliance with an opposing ring. However, the Sedy seal does not completely remain parallel; some degree of angular misalignment remains. This misalignment is probably due to the long length or thickness of the Sedy ring which thus has a high stiffness.

#FIG. 1 of the drawing is a cross-sectional view of a conventional prior art mechanical face seal;

#FIG. 2 of the drawing is a cross-sectional view of a typical seal ring and illustrates the pressures acting on the seal ring and the parameters of the seal ring;

#FIG. 3 of the drawing is a sectional view of a typical seal ring showing thermal distortion resulting from friction heating at the faces of the seal ring, which leads to uneven wear in a conventional prior art seal;

#This invention relates to a new and improved seal and seal ring design. The preferred seal of the invention comprises a radially compliant seal ring and a zero net thermal radial taper design.

#FIG. 1 illustrates a conventional type of mechanical face seal. The main parts of the seal are discussed below so that the novelty of the present invention can be described. The seal shown in Fig. 1 comprises two rings, a primary ring 10 and a mating ring 12, a shaft 14, a housing 16, seals such as O-rings 18 and 20, urging or compressing means such as a spring 22, a flexible drive arrangement 24, a retainer 25, and sealed fluid 26. The primary ring 10 is typically flexibly mounted so that it can uniformly press against the mating ring 12 due to action of the hydrostatic pressure created by the fluid 26 and the springs 22. Flexible mounting of the primary ring 10 requires a flexible secondary seal 20 which may be an O-ring type seal or a bellows, and a flexible drive arrangement 24 as shown in FIG. 1. The primary ring 10 may rotate with the shaft 14, as shown, or it may be flexibly attached to the housing 16. The mating ring 12 may be fixed to the housing 16 and sealed by the O-ring 18, as shown, or it may be attached to the shaft 14. The seal is formed at a sliding interface 28 or "face" between the primary ring 10 and the mating ring 12. The sealed fluid 26 attempts to flow across the sliding interface 28, which is generally a narrow radial passage.

#FIG. 2 shows a force diagram of a primary ring 10 in a seal; the lines illustrate pressures acting on this ring 10 during operation. The dashed line represents the center line of the seal ring. The parameters of the seal ring 10 are: an outer radius of contact r.sub.o 30, an inner radius of contact r.sub.i 32, and a balance radius r.sub.b 34. With these three parameters, the balance ratio of the seal, B, can be calculated according to the following equation: ##EQU3##