Efficient Plant July/August 2020 - 20

feature | lubrication solutions
Fig. 1: Impact of Water on Rolling-Element Bearing Life

The results of a study by Cantley show an empirical relationship between the amount of water in
oil and the life expectancy of a rolling-element bearing. Source: R. E. Cantley, ASLE Transactions
Vol. 20. 3. 244-248, 1977).

Fig. 2: Silica Gel Removes Environmental Water

Figure 2 shows the impact of using silica gel in breathers on two identical centrifugal pumps
operating outside in relatively high humidity.

humidity environment. Figure 2 shows the
impact on two identical centrifugal pumps
operating outside in relatively high humidity
(74% RH) and at high temperature (93 F).
Both pumps were filled with pre-filtered
oil to remove as much moisture as possible
and were equipped with bearing isolators

20

EP2007flube.indd 20

| EFFICIENTPLANTMAG.COM

to prevent contaminants from migrating
through the shaft-seal interface. In addition,
both pumps were completely sealed from
the outside environment by plugging the
breather/fill port.
By installing breathers with integrated
humidity sensors, the impact of controlling

headspace humidity using a silica gel desiccating medium is obvious. Without headspace humidity protection, the first pump
showed relatively high internal humidity,
which fluctuated between 55% and 65%
due to day/night temperature fluctuations.
Despite being nominally sealed, clearly air
exchange is occurring, likely through the
bearing isolator.
By contrast, the pump with headspace
protection maintained a very low internal humidity due to the silica gel actively
dehumidifying the headspace. Based on the
graph shown in Fig. 1, we can expect the
bearing life for the pump with dry headspace
to be 20% to 40% longer than the pump
with non-protection. This indicates that
bearing isolators and a desiccant breather are
required for maximum bearing life.
Similar effects can be seen in most, if not
all, wet-sump applications. For example,
measurements were made with two different
sets of splash-lubricated gearboxes, one with
active headspace humidity protection and
the other with no protection. Both sets of
gearboxes were operating outside in highhumidity environments. Water concentrations dropped from an average of 350 to 400
ppm without headspace protection to 70 to
80 ppm with active protection.
Much is made of solid-particle contamination, and rightly so-particles are the leading
cause of lubrication-related failure. However,
do not overlook the importance of controlling moisture. For wet-sump applications,
such as pumps and gearboxes, moisture is
just as likely to induce a failure. Make sure
you take every step possible to protect your
critical wet sumps. EP
Mark Barnes, CMRP, is Senior Vice President at Des-Case Corp., Goodlettsville, TN
(descase.com). He has 21 years of experience
in lubrication management, oil analysis, and
contamination control and has published
more than 150 articles and white papers.

JUL/AUG 2020

7/15/20 2:25 PM


http://www.descase.com http://www.EFFICIENTPLANTMAG.COM

Efficient Plant July/August 2020

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