Appeal No. 1997-0287
Application 08/263,034
thrust and axial displacement. Swearingen '768 controls the
valve based on sensing the axial shaft position. Swearingen
'689 and '768 do not disclose the fluid thrust balancing
system in combination with active magnetic thrust bearings.
Swearingen '689 and '768 indicate that the problem of
variations in axial thrust on the shaft of high speed rotating
machinery such as "compressors, turbines, turboexpanders"
(Swearingen '689, col. 1, line 15; see also Swearingen '768,
col. 2, lines 3-4) was known. The solution in the patents is
to use a fluid balancing system using a control valve to
balance the pressure between high-pressure and low-pressure
zones to offset the thrust on the bearings. The fluid thrust
balancing system is independent of the type of bearings. One
of ordinary skill in the art would have recognized that the
same problem of axial thrust exists in turbo machinery having
active magnetic bearings such as Andres and would have been
motivated to employ a fluid thrust balancing system as taught
in Swearingen '689 or Swearingen '768 in addition to the
active magnetic thrust bearings to offset the thrust load on
the thrust bearings. Thus, Andres and either Swearingen '689
or Swearingen '768 appear to be sufficient to establish a
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