I posted this a week or so ago at the eaglesoft forums and never got a response, so I thought I'd shop my question here to see if there are any resident Citation gurus in house:Here's my post:Simlulation aside for a moment, I have a question about the real Citation X that hopefully someone here can answer:By default, the engine bleed valves are placed in the LP position. The checklist calls for moving these to HP/LP prior to engine start, which presumably opens separate high and low pressure valves. This seems well and normal.My question is: does this switch act like a bleed toggle that draws from *either* the HP or LP ducts as demand requires it, or are both valves actually open at the same time? Is there a check valve in the LP duct which prevents back feed if the HP valve is open? I've read that in other aircraft, the HP valves are generally open when the engines are running but idling and pressure coming off the intermediate stage is insufficient. I've also read that running with the LP bleeds yields the greatest fuel efficiency. Does that apply here? Should the bleed valves be switched back to LP after takeoff? I realize this question wanders into esoteric trivia, and is perhaps beyond the scope of this forum, but I am curious if someone has an answer. Perhaps someone can point me at some good online resources that diagrams the pneumatic systems of the Citation X and or describe its operation?Thanks!J

J,I'm definitely not a "guru" but....Check out this site http://www.meriweather.com/10/citation.html and click on Forward Instruments at the top. Once on that page, you can click anywhere on the panel and get an explanation as to what each switch does. You might also do a search on the Internet too as I found several sites using the keyword Citation X. Hope this helps and you figure out those bleed valves.Jim