NrNg Np
variable
compressor discharge pressure (CDP)LOAD
T2 decrease
the prime boost pump, or the submerged boost
T2 sensor input to a bellows, balances push-bar
pump.
actuates a
inputs withCDP to maintainoptimumbellows which
DECELERATION FUEL
to fuel positions thefuel/airratio.Sumof bothinputs actuates
Ng shutdown
3-D
FLOWLIMITING aflappervalve. @110%Ng Shutoffvalve,stopsfuelflowtoengine injectors
PREVENTS LEAN DIE-OUT DURING
3Dcamradialy.
whenflyweights whenPCLisinoffposition.Fuelflowbegins toinc.ordec.
CAM Ng
RAPID POWER REDUCTIONS.
Flapper valve that varies fuelposition Ng servo
whenPCLisadvancedtoideldetent. Ngoutput
pressure used for hydraulic in contact with
T2 increase
Ng overspeed
T2
positioning of the metering
valve.
Flyweights rotateIAWNgspeed.
valve.
Minimumpressurevalve, preventsfuelflowuntil Npoverspeedswitch Ng servo They position the Ng servo via a forced
HMUcontrolpressureisadequatetooperateHMU signal(fromECU)ballanced flapper systemwhich uses fuel
systems that require hydrulic fuel pressure. Opens when to overspeed as hydraulic pressure, the Ng servo
fuelpressurebuildsto160psiaboveHMUcasepressure. solinoidinPOU.
verticaly positionsthe2D&3Dcams,
Ng increase
physical maximum
Valve is closed by Ngoverspeed valve @110%Ng to
this provides a mechanical Ng reference
fuel flow stop
for HMUmeteringfunctions.
2
prevent distructionwhich may occure @150%Ng speed.
@800 pph
MET ERI NG VA LV E
VAN E PUMP
1
300 psi output ( IDLE )
400-832 psi output ( FLY )
HIGH PRESSURE FUEL
HIGHPRESSURE METERED FUEL
physical minimum
HAMILTON STANDARD
fuel flowstop@60pph
Ng driven fuel returnto vane pump inlet when PCL is stop-cocked
JFC-78-4
axis "E"of AGB (9947rpm @ 100%Ng)
D-43
(1)
Vane Pump- The internal Vane pump is an Ng driven high pressure vane pump located inside the HMU. The vane pump increases fuel pressure to supply internal HMU fuel scheduling systems, and to pressurize metered fuel passages (lines) enroute to the start and main fuel nozzles/injectors. In the unlikely event of a simultaneous failure of both the submerged boost pump and engine driven boost pump, the HMU vane pump can suction fuel from the fuel cell (10,000 ft and below, assuming all fuel passages are intact). The main metering valve controls pressurized fuel from the vane pump to the Ng section.
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