What's the difference between outboard and inboard bearings?

Outboard bearings are mounted on the outside of a rotary valve’s housing, while inboard bearings sit on the inside of the endplates. Because they’re located closer to the seal, inboard bearings are typically associated with more frequent repairs and a greater risk of contamination. Outboard bearings leave a gap between the seal and bearings, which makes them safer and more reliable in the long run.