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The Practical Pumping Handbook .... .-~ii~ ::.:~:::. _ r ~

amount of beating friction and a longer beating life. It is worthwhile
noting however that, in the case of an extended interruption in the flow
of the oil mist, the beatings may be susceptible to premature failure.
The mist can be applied into the housing or directly at the bearings
themselves. The latter is generally used on bearings with a high thrust
load, or when the rotational speed of the shaft (in rpm), multiplied by
the bearing mean diameter (in mm.) is greater than 300,000. The oil
mist must be vented to the ambient atmosphere on the beating side
opposite the oil mist application to allow an effective oil mist flow
across the bearing.
Reliable operation of an oil mist system is dependent on the correct
physical layout and installation of the system. Also, special dewaxed oils
are recommended for use in oil mist systems to prevent clogging of the
mist fittings and other related problems. Manufacturers of oil mist
equipment should be consulted for specific recommendations in both
these areas.
It is worthwhile to be aware of the fact that a very high percentage of
users of oil mist lubrication systems have recorded significant cost
savings in the reduction of pump failures and direct maintenance costs.

7.7 Grease lubrication

Lubricating grease is essentially a soap thickening agent in mineral or
synthetic oil. When selecting the right grease, the base oil must be able
to satisfy the bearing's lubrication requirements.
The mixing of different types of lubricating grease is not recommended
as many of their contents and preservatives are incompatible.
The National Lubricating Grease Institute suggests different consis-
tencies of grease for various pump sizes and operating conditions.

9 NLGI No 1 - for large bearings running at slow speeds
NLGI No 2 - for roller bearings and medium-to-large size ball
bearings

NLGI No 3 - for small-to-medium size ball bearings; also in vertical
pumps, or pumps experiencing considerable vibration.
The following equation provides a general calculation of the interval
between bearing regreasings on a horizontal pump, and is based on a
bearing operating temperature of 70~ (158~ and using an average
quality grease.