e. Install dial indicators at upper guide and turbine guide bearing elevations. Two indicators,
90 degrees apart, should be installed at each elevation. To prevent errors in readings, ensure
that the dial indicators are in good condition and do not stick prior to installation.
Install plumb reading equipment. If plumb wires are used, install wires, plumb bobs, bases
for oil buckets, and banding on the shaft. If the Hamar system is used, install banding on the
shaft and sturdy steel bases for the laser in the turbine pit at north, south, east, and west
directions. The Permaplumb system should be mounted directly to the shaft, and the data for
the particular unit entered into the computer according to the manufacturer's directions.
g. Ensure that the thrust bearing high pressure lubrication system is operational. This may
require installing a temporary oil source for the pump.
h. One of the most important things to be checked before any readings are taken is whether the
shaft is free. A "free shaft" is essential for the readings to have any value whatsoever. The
shaft is free when the thrust runner is sitting on the thrust bearing and the rotating
components are not in contact with any stationary component. This means that all guide
bearings must be removed or backed off, packing or mechanical seals must be removed, and
the turbine runner should be somewhat centered in the seal rings. The shaft of a vertical shaft
hydrounit, when it is free, should be able to swing like a pendulum. A "free shaft" will move
easily a minimum of 0.005 inch in any direction with very light hand pressure, and, in many
cases, one finger is all that is required to start the shaft swinging. If a lever is required
between the shaft and the bearing housing to move the shaft, it is not free. A "free shaft" is
critical for several reasons. First of all, plumb readings are taken to determine the natural
position of the shaft and thrust shoes. If the shaft is touching anything that will prevent the
shaft from moving to its neutral position, no readings will be indicative of the true plumb of
the unit. The apparent straightness of the shaft can also be affected by the shaft contacting a
stationary component. Since we are working with thousands of an inch, if the shaft is put in a
bind, it can actually bend the shaft to the point that a plot of plumb data will show a dogleg
that may not exist. It is important to check for a free shaft before each reading because a
slight shift on the thrust block can cause contact somewhere on the shaft.
5.2 Plumb Readings
Plumb is the reference for all readings on vertical shaft alignments. While some measurements
are relative to the position of unit components, eventually all measurements are tied back to a
plumb reference. For example, bearing centers, seal ring clearances, and generator air gap
measurements are taken relative to shaft, turbine runner, and rotor, respectively, but they are all
tied together with the shaft plumb readings.
To determine the straightness of the shaft, two reading elevations are required on all shafts. Most
units have only a generator and a turbine shaft and, therefore, require only four reading
elevations, but on units that have an intermediate shaft, six reading elevations are required. The
bands on each shaft for the readings should be located as far apart as possible to improve the
accuracy of the plot. The top reading band for the generator shaft should be as high as possible,