compression. The bolts should be
tightened to uniformly compress the gasket. This
means going from one side to the other around the joint. Gasketed joints should be
retorqued after the unit has been in operation for 1 or 2 days.
Compression packing on wicket gate shafts and the turbine shaft should be installed
with the joints staggered 90 degrees apart. It is sometimes helpful to lubricate the
packing prior to installation. The packing manufacturer should be consulted for
recommendations for a lubricant and for any special instructions that may be
required for the type of packing being used. With all of the packing and the lantern
ring, if so equipped, in place, the packing gland should be installed finger tight. The
wicket gate packing can be somewhat tighter because of the limited rotational
movement of the wicket gates.
There should be generous leakage upon the initial startup after the installation of
new turbine shaft packing. The packing gland should be tightened evenly and in
small steps until the leakage is reduced sufficiently. The gland should be tightened
at 15- to 30-minute intervals to allow the packing time to break in. The temperature
of the water leaking from the packing should be cool or lukewarm, never hot. If the
water is hot, back off the packing gland.
Mechanical seals are sometimes used instead of compression packing on the turbine
shaft. The seal consists of sealing segments, usually made of carbon, held against
the shaft by spring tension and lubricated by a thin film of water. A grease zerk is
usually provided to lubricate the seals prior to startup following an overhaul or
Since mechanical seals are precisely made and rely on very tight tolerances in order
to operate successfully, a great deal of care must be taken during the installation.
Just a small amount of dirt or other contaminants on the polished sealing surfaces
can allow leakage past the seal and reduce the seal's life. The seal segments are also
usually very brittle and are easily broken. A spare set of segments should be on
hand in the event any should break.
If possible, the governor should be tested and adjusted prior to startup using a PMG
simulator. The PMG simulator provides a three-phase alternating current at a
voltage and frequency that matches the output of the PMG. The simulator drives
the ballhead motor at normal synchronous speed which makes the governor operate
as if the unit was online. If the PMG simulator is available, these tests can be
performed as soon as the servomotor and wicket gates are operational. The tests
are described in