Pipe union with both pre-load dependent and independent seals

摘要

A disconnectable union for fluid piping is provided in which a pre-load dependent first seal between disassemblable union members is coaxially related to a second seal operable independently of the pre-loading of the first seal such that the second seal independently contains any fluid that comes in contact with it even if such fluid contact is due to diminution of the pre-loading of the first seal. Various flange joint configurations and seal constructions are disclosed for both plastic lined and unlined metal pipe.