Thin articles such as letters are conveyed over a supporting fluid layer formed against a track surface along which they move. This layer is built up by jets issuing from nozzles located on both sides of the track surface and opening flush with the latter. The nozzles are oriented towards the center...http://www.google.com/patents/US4131320?utm_source=gb-gplus-sharePatent US4131320 - Conveyor device for letters, cards or other thin article
