Alignment and operability analysis of a vertical sodium pump Page: 4 of 11
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e. Subcritical-speed operation for mininm shaft whirling orbit, avoiding hysteretic
self-excited instability. Shaft-bending critical speeds always exceed the rumaing
speed by at least 2S. This margin is assured by sufficient bearing stiffness (varies
as angular speed squared), bearing pocket pressure, proper clearance, and depth of
pockets. The two liquid sodium hydrostatic bearings alleviate adverse effects of the
significant overhang associated with the double-suctic. impeller.
f. Tolerable axisywaetric clearance loss in the bearings under worst-condition upshock
or downashock thermal transients, by optimally sizing the journal thickneses and flow
holes to obtain close thermal cracking between shaft journals and bearing housing,
separately for the primary and the intermediate CREDg pumps, based on in-depth c-
pater finite elament/difference analysis.
g. Minimn tamperamure gradients in the flanges and shaft portion, which are submerged
below the liquid sodium level and posed to charmal transients; this is achieved by
means of thermal liners, shrouds, and flow beffles.
h. Heat-created castings, so that there is no significant densification or shrinkage of
the bearing housing and no unanticipated clearance losa from prolonged oaposure to
1,000-F sodium.
i. Sliding gudgeons between the pump tank and inner structure (which carries the bearing
housing), structurally decoupling thea with a clearance that is larger thea the
translations resulCing fros nasale piping loads or front cellular coaveccion Ln the
annular region between the pump tank and the inner structure.
j. Interchangeability of parts, since the quasi-fleible coupling is more forgiving to
assembly tolerances, assuring predictable vibration behavior even though the verti-
cally oriented pump lacks deed-weight biasing.
2. Alinment Analvsia
Gears, turbines, generators, compressors, valves, pimps, and motors offer a broad
range of problem involving mechanical vibrations and misalignment. As suggested by
references 1-23, it is essential to review the mechanical vibration problem caused by
misalignment and the methods of checking aisalignmeat.
The idaal case occurs when equipment is aligned to the designer's specification, thus
avoiding less-chan-smooth operation, which could lead to increased maintemeace and po.-
sible failure. However, camplicatios result partly from thernal expansion (the equipment
having been aligned when cold, not when operating) and partly from the appreciable difference
between static and dynamic conditions, e.g., primarily in gears. In the case of peepe,
loss of clearance in the bearings, coupled with shaft whirling, can cause metal-cormetal
contact, frictional localized beating, increase in bearing temperature, bearing seizure,
and a sudden dip in discharge pressure (due to speed decrease), especially during thermal
transients, necessitating shutdos.
A rigid coupling between pump shaft and motor rotor has the advantage of compectnes
but does not readily accomodate miselignmeat. It teeds to transmit it to adjacent equip-
fant; however, even a smell degree of flexibility enhnces the ability to accomndate it.
With a diaphragm-type flexible coupling, such as that selected for the Clii design, there
is little transfer of miselignment between adjacent parts. The coupling is also useful to
datume torsional resonance away from operating speeds. Diaphragm-type flexible couplings
are torque limited and are not practical from a size standpoint for motors emceeding 6,000
horsepower.3
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Gupta, V.K. & Fair, C.E. Alignment and operability analysis of a vertical sodium pump, article, January 1, 1981; United States. (https://digital.library.unt.edu/ark:/67531/metadc1107326/m1/4/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.