A320 Blue Hydraulic Abnormal
 

Hi Guys
Just doing a bit of revision. Of the three abnormals in FCOM. ie.
HYD B RSVR LO AIR PR
HYD B ELEC PUMP LO PR OVHT
HYD B RSVR LO LVL
In only the last failure the EMER GEN is inoperative but not in the first two. Would somebody like to elaborate please.

Simple answer is that the Emer Gen needs fluid to run. In the first two conditions you have it, but in the last you do not.

RAT powers blue system, which then runs the emergency generator.

HYD B ELEC PUMP LO PR OVHT = electric pump has failed, but the hydraulic fluid is still there. If you deploy the RAT, it will still power the emergency generator

HYD B RSVR LO AIR PR = the air pressure is low, which might cause hydraulic pressure to fluctuate, especially when manuevering and at high altitudes, but enerally it should still provide normal flow to the pump. No difference on whether you use RAT or the electric pump to pressure the blue system.

HYD B RSVR LO LVL = no or low hydraulic fluid quantity in the blue system. If the RAT deploys, it can't power the blue system, since there is no fluid. No blue system = no emergency generator.