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~- 1711-i ]1[[ I .............................. Pump Bearings

14.0 x 106
T = K 4d
nxqd
_. Grease service life (hours)
W
K = Factor for bearing type (10 for ball brgs.)
n - Pump rotational speed
d = Bearing bore (mm)
In spite of this calculation, regreasing intervals will have to be more
frequent than shown above when the bearings are operating at higher
temperatures, the bearing axis is vertical, or if (as shown later in this
Chapter) contamination is present. Conversely, the calculated interval
can be increased when the bearings are operating at lower temperatures
or if a higher quality and/or temperature greases are used.

A good rule of thumb is to schedule regreasing every 2,000 operating
hours or every 3 months, whichever comes first. It should be noted that
regreasing should take place only when the pump is not running.

7.7.1 Shielded bearings
A single shield on a bearing can
control the amount of grease
entering that bearing. The bearing
should be positioned in the pump
with the shield located on the side
towards the grease supply. This
allows sufficient grease to pass
through the shield clearance to %iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii~
lubricate the bearing and any
excess will pass through the
bearing.
Figure 7.16: Shielded bearing
This arrangement must be used
with some caution as some of the
newer shield designs require
higher pressures to fully inject the grease, yet too much pressure can
collapse the shield into the cage.

7.8 Bearing life

Many pump specifications require a bearing life stated in terms of an 'L-
10' fatigue life. The L-10 life is that which 90% of a sufficiently large
group of apparently identical beatings can be expected to attain, and
can be calculated as shown. In other words, only 10% of these bearings
will fail within that number of operating hours.

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