Three things will keep a turbopump from coming up to full speed. Two of
these are somewhat related, as they both trip the same safety in the
pump. That safety is a current limiter and/or time limiter. TPs will
have limits on how much current they are allowed to draw, or how long
they take to reach X percent of full speed. Either way, this can be
caused by 1) a bad bearing or 2) a leak in the instrument (which could
include a bad air leak valve, as others have mentioned). The third thing
that would prevent full speed is a bad controller.

Even though its only 2.5 years old, it could still be a bad bearing or
controller, if you have eliminated the possibility of a leak. I would
lean toward bearing, unless you really have had some severe power
disruptions and/or just happened to get a bad controller. Personally,
I've had good luck dealing with Eagle Instrument Services. They will
send you a rebuilt pump or controller and let you see if that fixes the
problem before you even pay them. Very safe and easy way to diagnose a
problem, if you don't have the controller interface reader. See their
info here http://www.eagleinstrumentservices.com/turbo.htm

Howard

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Howard Sanford
919-513-3039
North Carolina State University
Dept. of Soil Science
Box 7619
3114 Williams Hall
Raleigh, NC 27695
http://www.soil.ncsu.edu/services/sims/