Rebound Separator Valves replace the shock shaft nut with an asymmetric valve (provides a different flow rate in each direction of travel) to increase traction and improve bottoming resistance and pitch control.
Why is this needed? On a standard shock the Low Speed Rebound Adjuster flows the same on compression and rebound. In testing, when the lowest speed rebound damping is quick enough to get good traction, the lowest speed compression damping is too mushy. This causes a vague feeling and bottoming on long duration hits like big dips or gullies in Dirt. For Pavement RSV's have the added benefit of pitch control (front to back movement during acceleration and braking). This keeps geometry more consistent.
The Valve has a partially drilled bleed hole in the center. IT MUST BE DRILLED BY THE END USER TO THE PROPER SIZE (2.8mm).