A spiral retaining ring is found 'walked' out of its groove in a centrifugal pump. What is the root cause?

'Ring walk' or 'Spiral-out' occurs when the ring rotates relative to the groove and the end of the ring catches on a groove imperfection or is 'pumped' out by fluid flow/vibration. In centrifugal pumps, this is often caused by the hydrodynamic forces of the fluid acting on the 'gap' of the ring. If the ring's cling force is insufficient to overcome these forces, it begins to expand. Diagnosis involves looking for wear marks on the OD of the ring. The solution is to increase the ring's 'cling' by reducing its free diameter or using a self-locking design that prevents radial expansion altogether.