Of major concern is the radial leakage flow from the tip of
a centrifugal compressor stage down the leakage path and
into the labyrinth seal, as shown in Fig. 4.
In addition, the centrifugal compressor has an eye seal
on the cover of the impeller, a shaft seal between stages,
and a balance drum seal to provide axial force balance on
the rotor and in addition to seal the compressor’s highest
pressure condition. These are shown in Fig. 5. The balance
drum therefore has the longest axial length seal and the
greatest force levels acting on the rotor shaft.
For axial flow machines the seals can be on the blade
tips and between stages, as illustrated in Fig. 6.