The ferrofluid forms an oil ring inside it. The ferrofluid ring acts as a waterproof when rotating. Prevent corrosion by preventing the ingress of sea water and river water for a period of time. This increases the lifespan of the equipment. You can see the repairing video on our Youtube cahnnel https://www.youtube.com/watch?v=ejkORyBQZZs&t=188s