Handbook of Turbomachinery Second Edition Revised - Ventech!

Figure 30 LH2 turbopump rotor mechanical arrangement.
integral to the third-stage impeller. The axial force generated by the balance
piston is such that zero net rotor thrust is maintained while the turbopump
is operating. Additionally, the piston’s reserve force capacity at the design
point is somewhat in excess of 120,000 lb to resist any changes in rotor
thrust that may develop.
During start and cutoff transients, when full balance piston capacity is
not available, a large rolling element thrust bearing is provided to react to
rotor thrust, as shown in the figure. This thrust bearing is particularly useful
during the early portion of the pump start sequence, when pump thrust
forces have not fully developed. The pump thrust forces lift the rotor off the
thrust bearing when the turbopump rotating speed exceeds about 10–15% of
its design operating speed.
BEARINGS
The need for bearings in rocket turbomachinery is based on exactly the same
principles as in ground-based machinery. Generically speaking, bearings
provide the mechanical interface between rotating and stationary hardware,
and provide the points (or areas) over which loads are reacted. The forces
that must be reacted by bearings can include both radial and axial forces, as
well as moment loading or bearing ‘‘bending.’’ In addition, a bearing may be
required to transmit drive torque from turbine to pump through a drive
shaft. This combination of forces imposed on a bearing, as well as the
required angular velocity, will determine the required physical configuration
Copyright © 2003 Marcel Dekker, Inc.