Damage to the screw, barrel, or non-return valve can all lead to hang up areas as well as high shear locations that can lead to splay. Any area that traps material can result in material becoming degraded; as the material degrades it can release gases that will be trapped in the plastic melt stream and cause splay. Whenever a screw is checked for preventative maintenance, a part of the procedure should be to look for any damage to the screw, barrel, and non-return valve.