Shredding belts.

It looks like the PS Pump literally shutter stops when turned and the belt continues to spin on the stopped pulley? That's where all the belt dust is coming from all over my fan and engine? The dust buildup is right by the PS pump and on the fan. I checked it a couple times this last belt and was surprised that the belt seemed to be loosening up all the time so I tightened it up tighter and tighter. Actually the wearing was allowing it further into the grooves "loosening it" and expediting the process. I don't have a gauge but the pulleys all three look like they still have a solid V shape