A portable PSA device having a combination of features including a demand device to thereby limit the necessary size of the PSA unit itself; an improved spring loaded bed to permit horizontal use, and an arrangement of parts overall to produce a low profile, low center of gravity compact unit particularly...http://www.google.fr/patents/US4826510?utm_source=gb-gplus-shareBrevet US4826510 - Portable low profile DC oxygen concentrator
