Cavitation and water questions
A few questions related to cavitation and one on water content:
1. Have there been any other reports at all of cavitation damage in any HP pump used in 777 or any other similar Boeing 7 series aircraft? I assume that fuel which has not been degassed never normally causes cavitation in HP pumps during takeoff or climb.
2. From before TOD but particularly below flight level 170, what volume of air would be entrained (or possibly dissolved) in solution in the fuel in each of the main tanks as a result of the continued operation of the centre tank fuel scavenge pumps after the 900kg rump of fuel was scavenged?
3. Would degassing be inhibited by relative coldness of fuel or its relatively high boiling point (corresponding to relatively low fuel freezing temp)?
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?
5. Would cavitation in the HP pumps, once developed, release sufficient gas that the flow downstream would be reduced without any other restriction upstream of the HP pumps, or is the cavitation merely a secondary effect, possibly exacerbating but otherwise only symptomatic, of restrictions upstream of the HP pumps?
6. Might the suction feeds be blocked in descent (as they can be in climb) through degassing?
7. What amount of water is “excessive” in the 5.1/5.4 tons or so of fuel in each main tank ... 5, 50, 500, 5000 grammes? I guess 134 gallons or so in the 80 T centre tank is “excessive” giving rise to an alert, but does that mean that less is not?!