On Sun, 2004-01-25 at 22:13, John Carmack wrote:
> We always run to propellant exhaustion and just let the tank purge through
> the engine.
That is one possible approach... but as you get to more and more
sophisticated vehicles, it becomes less and less viable. XCOR has a neat
way of doing it -- the drill purge ports into the downstream side of
every valve. They then hook each of these up, through a check-valve, to
a low pressure nitrogen source. When the system is at operating
pressure, the check valve prevents any N2 from flowing. When the
operating pressure drops off as a result of valve closure, N2
immediately begins to flow and purges everything downstream. Elegant
and effective. Obviously, there is a main purge control valve that is
opened at engine light and closed a few seconds after shut down.
-p
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