Page 211 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Compressor Best Practices Best Practice 3 .20

Fig 3.20.7 Impeller thrust force

Fig 3.20.8 Rotor thrust force

It is very important to note that a balance drum is used only or may not be true depending on the thrust balance system
where the thrust bearing does not have sufficient capacity to design. And even if it is, the thrust is zero only at one set of
absorb the total compressor axial load. And the effectiveness of operating conditions.
the balance drum depends directly on the balance drum seal. Figure 3.20.9 shows a rotor system designed four (4) dif-
Fail the seal (open clearance significantly), and thrust bearing ferent ways. Note how the thrust always changes with the flow
failure can result. rate regardless of the design. Another misconception regarding
A common misunderstanding associated with balance drum thrust balance systems is the normal or ‘active’ direction of
systems is that a balance drum always reduces the rotor thrust to thrust. In many cases, the active thrust is assumed to always be
zero. Refer to Figure 3.20.9 and observe that this statement may towards the suction of the compressor.

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