Rigaku Superseal Solid Shaft Ferrofluid Ferromagnetic Rotary Motion Feedthrough for bulkheads 3/4 in. to 1 in. thick, with transmission torque of 160 lbs-in.
Rigaku Part Number FD-LSR-0375-LC, 605353

These Rigaku vacuum rotary feedthroughs are designed for 3/4 to 1 inch thick bulkhead port connections. They are a ferromagnetic sealed device which uses dynamic sealing to allow free rotation of a solid shaft. These high performance vacuum rotary motion feedthroughs have the following features:

Maximum Rotary Speeds Up To 5000 RPM (no-load)
Maximum Bearing Load Capacity Of 575 lbs
(0.34) inch Diameter Shaft
Designed for 3/4 to 1 inch Bulkhead Connections
Maximum Operating Differential Pressure 37 psig (2.5 Atmospheres)
Helium Leak Tested To 5x10-09 std cc/sec
Transmission Torque 160 1bs-in
Ferrofluid Base Hydrocarbon Oil
A300S Ferrofluid With Vapor Pressure 1x10-10 Torr
Maximum 80 Degrees C Operating Temperature
Housing and Shaft Material 17-4 PH SS
Fomblin/Krytox Blend Bearing Lubricant, Vapor Pressure 1x10-13 Torr
Suitable For Operating To 1x10-08 Torr
Rigaku Part Number FD-LSR-0375-LC (605353)

The vacuum tight dynamic seal is formed by the ferromagnetic particles suspended in the magnetic fluid (A300S) which interacts directly with the magnetic field generated by the feedthrough's internal magnets. In these rotary feedthroughs, narrow rings of fluid (shown in figure below) forms a liquid barrier filling the annular spaces (or gaps) between a rotating shaft and the tips of the stationary pole magnetic piece. Since magnetic fluids can be pushed, pulled, and shaped by magnetic field they remain stationary to form a vacuum tight seal. Radially, the fluid rings are bounded by the magnetic pole piece tips. Magnetic flux density at the pole tips is very large. Hence, any axial displacement of a liquid ring away from the pole tip results in a force that resists the displacement. The isolated volumes between adjacent rings are important in the functioning of the device.

Several different arrangements of housing, bearings, magnets and fluids are used for the many types of rotary vacuum feedthroughs. Many factors must be considered when selecting a rotary feedthrough for your process. A "Magnetic Fluid Feedthrough Primer" in PDF format is provided for download here that explains the technical functions and applications of magnetic fluid rotary feedthroughs. Topics include:

Basic sealing principles of Dynamic Sealing
Design of a feedthrough
"Superseal" A breakthrough in construction and reliability
Application Factors - environmental and mechanical
Impact of feedthrough on process
Impact of process on feedthrough
Materials feedthrough is made of
Application examples