For water, waste water, chilled water & many other services, to permit pipelines “flex” a bit. Metallic pipes expand and contract when the ambient (or service) temperatures vary and non-metallic pipes (which may be buried) will move with ground settlement etc. Where probable movement can be envisaged the values are designed by a compensator which can flex, thus avoiding undue pipeline damage. Interesting applications are reservoir inlet/outlet connections, pump connections, differing flange standards either end, axial or angular offset of new to old pipelines. Sizes from DN50 to DN5000 and pressures of PN6 to PN25 on rubber, but the larger sizes would be lower pressure capability.. Higher pressures and temperatures in 316SS.