http://www.thebluealliance.net/tbatv/match/2010kc_qm36
You can see team 1810 deploy the balloon thing around 3:19. By all appearances, it's a low pressure device - once it's deployed, they go into the tunnel enough to hit the balloon, which knocks it over... and it just doesn't have the strength to pick itself back up again. This, combined with the incredible volume of the balloon and the quick fill rate, lead me to believe it's done with a fan, not the compressor/pneumatic system.