Leak Rates of a Candidate Main Interface Seal at Selected Temperatures

Abstract

The leak rate of a 54 inch diameter composite seal assembly was quantified at selected temperatures as part of developmental work for the National Aeronautics and Space Administration Low Impact Docking System (LIDS). The 54 inch diameter composite seal assembly studied was representative of the 58 inch diameter LIDS main interface seal. This near-full-scale seal assembly consisted of elastomer seals (Parker Hannifin S0383-70) molded into an aluminum retainer. To mimic the mission operational configuration, the seal assemblies were mated in a seal-on-plate test configuration. Tests were completed for fully compressed and partially compressed seals. The composite seal assemblies were subjected to test temperatures of -30◦C, +20◦C, and +50◦C (-22◦F, +68◦F, and +122◦F) which are representative of the docking system operating temperatures. In addition, comparisons of the 54 inch diameter composite seal assembly leak rates to those of a similarly designed 12 inch diameter subscale composite seal assembly were made to determine how well the near-full-scale leak rates were predicted by subscale tests. Observed leak rates were exponentially proportional to the test temperature due to the relationship between permeability and temperature. In the fully compressed test configuration, the near-fullscale leak rate increased by a factor of 3.89 from the lowest test temperature to the highest test temperature whereas the subscale seal assembly leak rate increased by a factor of 3.37 over the same temperature range. Leak rates were normalized per linear inch of seal for a direct comparison between the full-scale and the subscale assemblies; normalized leak rates of the near-full-scale seals were 2.21 to 2.65 times greater than the subscale leak rates. The difference in the normalized leak rates between the near-full-scale and subscale assemblies was attributed to an additional leak path in the near-full-scale test hardware that was not present in the subscale test hardware. At each temperature and compression level, the leak rate of the near-full-scale composite seal assembly was below the LIDS main interface seal leak rate allocation of 2.5x10−3 lbm,air per day.