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Transmission Elements for High-Speed Turbomachinery 265

13.5.5 Lubricant oil containment on gear and
variable-speed units
Measures have to be taken to limit contaminant ingress into lubri-
cating oil. Whenever a gap exists between the rotating shaft and the
surrounding stationary housing components, these housings will
“breathe,” as illustrated in Fig. 13.20. Gearbox manufacturers have
used lip seals for bearing protection and oil containment for many
decades. However, lip seals are subject to wear and must be replaced on
a time-based preventive maintenance schedule. If lip seals are not
replaced in this manner, they will allow contaminants to enter because
of pressure differences between the gearbox interior space and the
ambient atmosphere. (See Fig. 13.20.) Thus, there is serious risk of
water vapor entry and condensation, with the likely outcome shown in
Fig. 13.21. A wear groove in the shaft is also clearly evident in this
illustration.
Recognizing the limitations of lip seals for longer-term contamina-
tion control prompted the American Petroleum Institute (API) and
many equipment users to seek and recommend superior preventive
measures. Alternative sealing devices include both rotating noncon-
tacting labyrinth bearing housing seals and rotating contacting dual-
face seals. All styles are collectively called bearing isolators or bearing
protector seals. Please to refer to the discussion of bearing protector
seals in Chap. 7.
Various factory tests and a thorough review of field experience have
established the viability and effectiveness of cartridge-type magnetic

Figure 13.20 Expulsion and induction of surrounding air in an elementary
labyrinth seal.