When the chambers equalize, when you push the seal past the dimple, the chambers will have the same pressure. Bear in mind at the same time the negative chamber is expanding in size for a small time as this happens. When the fork goes back to it’s resting position, the size of the negative chamber has shrunk relative to when it was being equalized. Suddenly the 70PSI at the equalization volume is under pressure and is more than 70PSI, say 80PSI. This is the negative force that pushes the fork into its travel. When the negative chamber is too big or has to much pressure in it, you get fork suck down, which was happening to the B1 forks. The same can happen if you let all the pressure out of your fork too quickly or if the equalization port is plugged with grease and the negative chamber cannot release its air.