Handbook of Turbomachinery Second Edition Revised - Ventech!

integration of impeller exit pressure shows radial loads that are nearly zero
(at or near the design flow coefficient), and this result has been substantiated
many times in instrumented pump tests.
A point should be made here with regard to the issue of volute sizing.
We have shown earlier that since the volute occupies the largest radius in a
typical pump, and is subjected to the highest pressures, its weight is a
substantial fraction of the total pump weight. As such, it is quite tempting to
conserve pump weight by deliberately sizing the volute ‘‘small.’’ This design
choice increases fluid velocities within the volute for a given mass flow rate.
If this is allowed to go to extremes, off-design pump operation may result in
extremely high bearing loads and correspondingly short life. It should be
pointed out that off-design operation can be induced either by a variable
thrust engine system or simply by volute/impeller mismatches due to
manufacturing tolerances. If an aggressive volute-packaging scheme is
sought, careful attention should be paid to the interactions between the
propellant pump and the rest of the engine system. In addition, pump radial
loads should be computed for component parts that span the range of
allowable manufacturing tolerances.
If excessive radial thrust loads exist due to volute geometry, a number
of alternative discharge schemes exist to minimize this problem. Examples of
this are shown in Fig. 19. These approaches seek to establish an impeller exit
pressure profile that is as symmetric as possible.
Figure 19 Some examples of centrifugal pump volute configurations.
Copyright © 2003 Marcel Dekker, Inc.