Apu Flashcards
What are the 3 major components of the apu?
-turbine assy
-combuster assy
-reduction and accesory drive assy
State primary and secondary function of the apu
Provides bleed air for pneumatic power,
provides shaft power for driving the accessories
What type of compressor is fitted to the apu
Centrifugal
Where is the combustor drain valve located?
At the bottom of the combustor
What pressure does the combustor drain valve open
Below 5psi
Inputs from which 4 components are used by the esu to monitor and control apu start and steady operation
Egt thermocouple
Mag speed pickup
Low oil pressure switch
High oil temp switch
At what soeed is the apu start motor deenergised
70 percent
Does apu start bypass valve open to bleed off bleed air from compressor?
Yes!
When the bypass valve is open does air get directed back into the compressor inlet
No
Will apu start bypass valve close during main engine start to ensure max bleed air is available to the engine starter
Yes
If the esu shits down the apu, what must not be done before bite readings are taken
Make sure apu power and dc switch is not cycled as this will reset the indicators
What limit condition will not result in the apu shutting down
High oil temperature
During start cycle when will the following fuel solenoid valves open?
-start valve?
-main fuel valve?
-max?
-5%
-14%
-90% 1.5-3.5s
During apu start cycle what rpm range are both start and main solenoid valves open?
14-70%
As apu speed increases, pressure increases, what effect does pcd pressure have on the acceleration control unit
Opens metering valve resulting in more fuel
