This optional device extends the range of applications of the vacuum follower plate for bubble-free material supply. The expanding ring contains an inflatable seal, which spreads the vacuum follower plate during docking to the material container. This ensures a perfect seal between the follower plate and the inner wall of the pail. The new expanding ring thus enables a bubble-free material feed from conical containers. Even variable container sizes (inner diameter 281.5 - 288 mm) can be reliably covered.