Coupling Assembly, V-Retainer, High Pressure High Temperature, Pneumatic Tube
This SAE Aerospace Standard establishes the requirements for a V-retainer coupling, flanges, and seal suitable for joining high pressure and high temperature ducting in aircraft bleed air systems. The rigid coupling joint assembly, hereafter referred to as “the joint”, shall operate within the temperature range of -65 to +1200 °F.
Rationale: AS1895, /1, /4, /7, /20, /22 and /23 have QPL requirements but manufacturer’s are having difficulty qualifying as the specification is written.
The seal (/7 and /23) test requirements were interpreted differently for the seal manufacturers and the QPG. The seal manufacturer’s tested using low profile only and the QPG wants both standard and low profiles tested. The specification does not clearly state this. The specification needs to define a way to qualify the seals.
The /4 low profile material table should be harmonized using both A286 and Ni718 for all sizes.
The bolt callout in the procurement spec and the coupling parts standards versus the AS4108 spec needs to be consistent. AS1895 requires AS4108 bolt at 160-190 ksi. AS4108 is 160 ksi min.
Add maximum limits to torsional moment tests. Currently the specification states “not permanently deform or rotate”. Suppliers are using dial indicators for this and small displacements measured are likely the clearances within the couplings components. Add scope to change wording in section 3.5.4 to “no visual angular displacement allowed when subjected to torsional moment specified in Table 5.” No change required for corresponding torsional moment test section 4.5.3.