Magnetic fluid (ferrofluid) fills a small annular gap between a rotating shaft and a stationary magnetic pole piece. The gap is part of a high-energy magnetic circuit which includes the shaft and pole piece. The very large magnetic flux in the gap exerts a force on the fluid, holding it in place against pressure difference from atmosphere to vacuum, yielding a dynamic rotary seal in which there is no solid friction. Therefore, very long operating lifetimes are achieved.

Because the magnetic fluid has very low vapor pressure, it remains permanently in place for the entire lifetime of the seal, and does not contaminate the system. Some applications have special requirements (high temperature, highly reactive gases) which can be satisfied by selection of the optimum fluid from our family of fluid materials.