The results portion of the computer program provides the total out of plumb data for the center of
runout in mils per inch. There is also an automatic out-of-roundness check to check for accuracy
of the readings.
Units with self equalizing bearings cannot use the Permaplumb system because it is not possible
to obtain a static runout check. With the Permaplumb system, it is difficult to accurately
determine dogleg in the shaft, and there is no way at all to check for offset at the coupling.
Limited wire or Hamar laser readings may be used to check for shaft straightness, but if the static
runout diameter is acceptable at all of the guide bearing journals, the straightness of the shaft
should not be critical.
5. BASIC MEASUREMENTS
The position of the generator and turbine shafts relative to plumb and the stationary components
need to be determined. Also, the straightness of the shafts and the perpendicularity of the thrust
runner to the shaft has to be addressed.
5.1 Preliminary Checks for All Units
a. Use a precision machinist level to level the upper bridge (the lower bridge on umbrella units.)
Check for any "soft feet" condition on any of the bridge legs. A "soft foot" condition is
similar to short leg on a four legged table and if left uncorrected, can cause distortion of the
bridge. Check for a "soft foot" by first checking that all bridge leg bolts are securely
tightened. With a dial indicator, check the rise of each leg as its mounting bolts are loosened.
Retighten the mounting bolts after the rise is recorded, so that only one leg is loose at a time.
If one leg rises more than the other legs, it is a "soft foot" and shims should be placed under
that leg to correct the condition. For example, if one leg of a six leg bridge rises 0.025 inch
while the other five only rise 0.015 inch, a 0.010 inch shim should be added to the "soft foot."
There may be more than one "soft foot." Shims should be added accordingly so that the rise
of each leg is nearly the same.
b. Allow the thrust block to cool over night after installation before any readings are taken.
c. Establish direction convention for readings so that all readings agree. Directions don't have
to match actual compass directions as long as all readings are consistent and everyone
involved with the alignment understands the convention used. For example, many plants use
upstream and downstream for directions.
d. Remove packing and guide bearings. Install four jacking bolts with bronze heads at the upper
guide bearing elevation or, if the guide bearing is a segmented shoe type, install four guide
bearing shoes. Four jacking bolts installed at the turbine guide bearing may also be useful.