Page 211 -

The Practical Pumping Handbook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

which, under most operating conditions, would be considered perfectly
adequate. Unfortunately this would only be appropriate if the shaft
sleeve were shrunk onto the shaft where it contributes to the overall
strength of the shaft.
If, however, the sleeve is a hook type or keyed to the shaft, it actually
detracts from the shaft strength. Under such conditions, the SSR is
calculated with the use of the shaft diameter underneath the sleeve at,
say, 1s/8 inches in diameter, revealing a value of SSR of 143 which is
almost double the previously calculated value. This identifies a much
weaker shaft that is almost twice as susceptible to deflection in the event
of a hydraulic upset condition.

The good news is that this can be quickly corrected by eliminating a
shaft sleeve from the pump and using a shaft with a lS/8 inch diameter
in that area, thus reestablishing the shaft strength.

It must be noted that high levels of SSR will only be a problem if the
pump is required to operate under conditions where high radial loads
will be in effect. For further details on these radial loads, please refer to
Chapter 2.5.1.

11.5 Failure modes

The following lists the major parts of a pump and the failure conditions
that tend to show up in these parts, together with a guide towards the
possible underlying causes of the failures.

This list should not be considered as being complete, as every industry,
every plant and almost every pump, has its own set of peculiarities that
show up in pump failure. Consequently, the items and recommended
actions identified should be considered only as a guide towards the
achievement of pump reliability.

11.5.1 Impeller
Impeller clogging

9 Check pump operation
9 Check for change in pumpage
9 Check impeller clearance

9 Change to non-clog impeller design
Impeller imbalance
9 Balance impeller

lm 190