Page 105 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Pump Best Practices Best Practice 2 .20

Fig 2.20.3 Single stage overhung pump (Courtesy of Union Pump Co.)

failure! Hopefully, this exercise has clearly demonstrated why attention must be paid to the quality of the water used, the type
components, especially bearings, can suddenly fail for no ap- of grout and the method of grouting followed.
parent reason. These facts are presented in Figure 2.20.14. It is strongly recommended that an epoxy grout be used for
Figure 2.20.10 has been modified to show the force path all rotating equipment and a grouting procedure, approved by
from excessive discharge flange loadings to the bearing bracket. a reputable epoxy grout manufacturer, be utilized.
Figures 2.20.11 and 2.20.12 show the orientation of external Fig 2.20.16 has an important message: ‘If you suspect ex-
flange forces and moments that are referred to in Table 2.20.1. cessive pipe stress and/or soft foot forces, get out and thor-
Table 2.20.2 shows that the allowable forces and moments oughly walk around the affected machine’.
for most pumps are very low!

Condition monitoring indications of
The root causes of excessive pipe stress excessive pipe stress and soft foot
and soft foot
At this point, we have covered the function of the two most
Refer to Figure 2.20.13, the machinery environment. An asso- important components in rotating equipment:
ciate of mine has a favorite quote regarding the machinery
environment. Bearings
‘Stand at the equipment unit and rotate yourself 360 . Ev- Seals

erything that you see can and will affect the reliability of this The components which are most commonly affected by ex-
piece of machinery’. cessive piping and/or foundation (soft foot) forces are the
As shown in the last section of this chapter, the cause of bearings and couplings, although seal reliability can also be af-
component failure is the excessive forces exerted on the
fected. Figures 2.20.17 and 2.20.18 present the parameters to
equipment from: monitor, as well as the limits for anti-friction and sleeve type
The piping radial bearings.
The foundation (soft foot) As previously stated, excessive pipe strain and soft foot exert
forces beyond the design limits on equipment components. In
What then are the possible causes? There are many. We will the case of bearings, the forces will be transmitted from the
divide the possible causes into the following categories: source (pipe and/or foundation) through the casing, to the
bearing housing, to the bearing. Figure 2.20.19 shows how to
Design
Construction determine by condition monitoring if there is a pipe stress and/
Plant conditions or soft foot problem.
Once the root causes of machinery component failure are
The possible root causes are presented in Figures 2.20.14, suspected, they must be confirmed. Once confirmed, a cost-
2.20.15 and 2.20.16. effective action plan must be developed that will ensure
There have been numerous examples, especially in the Middle implementation at the earliest opportunity. This section pres-
East, of poorly prepared foundations and grouting. Careful ents this important information.

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