The Horizontal Steam Turbine For Stationary Plants 1920
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gear. Usually, however, in a direct pressure
feed system, only one pump is employed and
this pump must deliver all the oil under
sufficiently high pressure to work the gover-
nor gear.
If, for any reason, the oil pressure fails be-
low that required, a piston in the go vemor
gear, held up by the oil pressure, falis and
causes the steam supply to be shut off. The
turbine will usually come to a stop before
the oil supply to the bearing is sufficiently
reduced to cause damage.
Where an elevated tank is employed,
sufficient oil is usually assured to lubricate
the turbine for at least thirty minutes,
should the oil pump fail to work.
When starting up a turbine, where there
is no elevated tank, the oil supply to the
bearings will not be adequate until the tur-
Fig. i o. Ring oiled turbine bearings
bine is running at about one-quarter normal
speed. Therefore, before starting up a
turbine, it is necessary to apply oil to the
bearings by means of a hånd or an auxiliary
power-driven oil pump.
An auxiliary steam-driven or electrically-
operated oil pump is employed for large
turbines. As soon as the turbine reaches
normal speed the auxiliary oil supply should
be cut off, after which the oil pump, auto-
matically operated by the turbine, will
supply the requisite quantity of oil.
Ring Oiled Bearings (Fig. 10)
The bearings (F2) have oil reservoirs (F3)
from which the rings (F4) suspended on the
shaft (F) continuously carry oil to the shaft,
distributing it through a longitudinal groove
over the entire bearing surfaces. The oil,
as it leaves the ends of the bearings, drops
back into the oil reservoir.
Occasionally the bearings (F2) are fitted
with Sight Feed Drop Oilers, which feed a
certain number of drops per minute into the
bearings. In such cases the oil, when leav-
ing the bearings, is caught in "sa ve-al Is,”
filtered and used again.
This system, however, is obsolete and has
been superseded by the ring-oiled bearings,
which are now generally used on small tur-
bines.
OIL
Oil Qualifications
Correct high grade oils, specially manufac-
tured for turbine lubrication, are least af-
fected by the presence of air, water and
other impurities.
The use of the correct oil will eliminate
wear and manifest efficient lubrication in
terms of low bearing temperatures.
With an incorrect grade of oil, the bearing
temperatures are always extremely high. The
rate of oil oxidization—generated by the
great heat—is thus increased, so that fre-
quently the life of an ordinary oil in a tur-
bine is only a few months.
Circulation oils have been specially treated
to produce ready separation, and to with-
stand contamination with impurities under
the severe conditions of continued service.
When the operating conditions are extreme
and impurities collect in the system, the oil
in its circulation conducts to the journals and
bearing metals those impurities, which may
cause their corrosion.
The most prominent failures of oil in cir-
culation systems have been in turbines where
the surface speed of the journals was high,
the oil circulation rapid, with a practical cer-
tainty of water collecting in the system and
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