Just found this update on the site about Xcelerator. Has some good pics from www.twistedrails.com and also if you scroll down you'll find a pretty informative and simple animation of how the hydraulic launch work. It's a german site so it's not in english. But you get pretty much the whole idea. So those who can't sleep at nights because of the hydraulic mystery take a look at http://www.coastersandmore.de/Rides/Xcel/xcelmain.shtml
If only the site was in English, we could refer those asking about the launch to this site....
