A differential pumping seal apparatus includes a differential pumping seal for sealing a first space and a second space from each other in a non-contact manner, and a back up seal mechanism for sealing the first space and the second space from each other in a contact manner. The back up seal mechanism...http://www.google.de/patents/US20030075871?utm_source=gb-gplus-sharePatent US20030075871 - Differential pumping seal apparatus
