Fuel System -Cont.

T-34C AIRCRAFT SYSTEMS FAMILIARIZATION

CHAPTER FOUR

WORKBOOK

CHANGE 2

The fuel then reaches the engine-driven boost pump, where during normal operation, it draws

fuel from the sump tank and delivers it under pressure to the primary pump. The engine-driven

boost pump is mounted to and driven by the external oil scavenge pump on the accessory

On the discharge side of this boost pump is a fuel filter located on the left side of the firewall. A

handle to drain the filter is located on the firewall near the filter. In the event this filter becomes

clogged, there is a bypass valve to prevent a "flameout" due to fuel starvation. Also, a loss of

boosted fuel pressure as sensed by the boost pressure sense switch (Fuel Pressure Transmitter),

located on top of the fuel filter, will cause the steady illumination of a yellow FUEL PRESS light

on each annunciator panel and a flashing MASTER CAUTION LIGHT. Activation of the

electric standby boost pump should restore boosted fuel pressure and extinguish the light.

NOTE

Due to a time limit on solitary (unboosted) operation of the engine-

driven primary fuel pump, the pilot is required to log the amount of

time the FUEL PRESSURE light is illuminated and report it to

Maintenance.

The fuel flow transmitter, located next to the fuel filter, senses and converts fuel flow rate to a

26-Volt Alternating Current (VAC) signal and sends it to the fuel flow indicator in each cockpit.

Prior to entering the primary fuel pump, the fuel is heated with warm oil in an oil-to-fuel heat

exchanger in the range of 70 90 degrees Fahrenheit.

The primary fuel pump is a positive displacement gear type pump mounted on and driven by the

accessory gearbox. The pump supplies fuel under high pressure to the fuel control unit. Fuel

enters the pump through a micron inlet screen and exits through a pump outlet filter. Failure of

the primary pump results in flameout.

The fuel control unit (FCU) is a hydro-pneumatic-mechanical control device mounted on the

primary fuel pump and it meters the amount of fuel supplied to the combustion section according

to engine performance and power control lever position. The FCU uses P3 air as a reference to

monitor engine performance and control fuel output. Just prior to entering the FCU, this air line

has a P3 air filter on the right side of the engine accessory section. The power control lever

(PCL) is mechanically linked to the FCU through a cam box assembly. Another mechanical

input to the FCU is the condition lever which, when moved forward out of the OFF position,

opens the fuel OFF and ON valve, allowing fuel flow to the fuel nozzles. Full aft movement of

this lever secures fuel flow to the fuel nozzles. In response to the various input conditions, the

fuel control unit controls fuel flow to:

Set engine power, according to the position of the PCL or Emergency Power Lever (EPL).

Provide or shut off engine fuel, according to the position of the condition lever.

FUEL SYSTEM

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