4. Given no cavitation damage in LP boost pumps, should cavitation be assumed to be due to either (a) the higher rotational speed and/or design of the HP pumps coupled with something causing nucleation, (b) the formation of a restriction downstream of the LP boost pumps but upstream of the HP pumps or (c) a restriction upstream of LP boost pumps insufficient to cause LP pump cavitation damage?
Once again, the discharge of the HP pumps is indeed at high pressure (
) to overcome the compressor discharge air pressure and feed the burner. Thus any air or vapor content would be compressed to a very small volume, if not redissolved completely.
And the HP and LP pumps are quite different in design. The HP is of necessity a positive displacement type - gear type or vane type etc. Since it is such, the inlet can readily suck enough vacuum to cavitate if the LP pump isn't performing.
The LP pump is designed to tolerate a certain degree of gas/vapor/air in its inlet, which is its assigned job in protecting the HP pump. I think it may be a axial or centrifugal, non-positive displacement type -- but I'll defer to someone with more detail.