comprise the inner shell of the combustion chambers.
(pneumatic governor). Other components of the
The liners are perforated with holes and slots of correct
system are six fuel atomizer assemblies, a fuel shutoff
sizes and locations for proper control of combustion.
and drain solenoid valve, an air-pressure-ratio solenoid
S i x c r o s s - fi r e t u b e s a r e c e r a m i c c o a t e d a n d
va l ve ( t w o - s p e e d va l ve ) , a n a c c e l e r a t i o n a n d
interconnect the six combustion chamber liners. One
overtemperature control thermostat, a plenum drain
igniter plug is mounted on a pad on the No. 5
valve, and a normally closed auxiliary fuel solenoid
combustion cap assembly to provide ignition. Six fuel
valve.
atomizer assemblies mount through the combustion
The system functions to provide fuel for
chamber caps and into the ends of the combustion
c o m bu s t i o n a t c o n t r o l l e d r a t e s u n d e r va r y i n g
chamber liners to provide proper fuel spray. The two
conditions of engine speed, load, and discharge
pair of fuel manifold assemblies attached to the fuel
temperature. Fuel from the fuel supply is filtered by a
atomizer assemblies distribute the fuel supply.
replaceable filter element and pumped by the fuel
control to the fuel atomizer assemblies. Fuel flow is
Compressor Section
metered by the fuel scheduling valve (pneumatic
governor) during starting operation and by the
The compressor assembly section consists of a
mechanical governor during normal operation.
rotating assembly, housings, eight crossover ducts, and
a plenum assembly. The rotating assembly includes a
After the engine start switch is actuated, and when
first-stage, dual radial wheel and a second-stage, single
engine oil pressure reaches a preset value, the primary
radial wheel mounted on a common shaft, wheel
contacts in the oil pressure switch close and energize
shrouds, and housing. A torsion shaft is driven by the
the ignition unit. Within 1 psig following the primary
turbine rotating assembly. It is coupled to the internal
contact closing pressure, the oil pressure switch
spline of the compressor shaft and drives the
secondary contacts close and energize the fuel shutoff
compressor rotating assembly. The impeller wheels
and drain solenoid valve. This closes the fuel drain
and shaft are supported by bearings and bearing
section and opens the primary side of the flow divider
housings on each end of the shaft. The bearings are
valve in the normally closed fuel shutoff section to
pressure lubricated, and seals are installed between the
permit fuel flow to the fuel atomizer assemblies. When
wheels and adjacent bearings to prevent leakage of
fuel pressure reaches 125 psig, the flow divider valve
lubricating oil into the compressed air system.
opens completely to provide full fuel flow to the fuel
The rotating assembly is mounted in support
atomizer assemblies.
assemblies and housings. Crossover ducts direct the
Fuel spray into the combustion chambers is
compressed air from first-stage to second-stage
accomplished by dual orifice fuel atomizer assemblies.
impellers. A diffuser housing directs fully compressed
The smaller orifice in the atomizer provides proper fuel
clean air into the turbine plenum. The compressor
atomization at lower fuel pressures; a combination of
plenum assembly envelops the other compressor
smaller and larger orifices provide proper fuel spray at
assembly components and provides screened inlets for
higher fuel pressure.
the compressor air supply.
Control of fuel flow to maintain required engine
SYSTEMS OF THE ENGINE
speed is provided by action of the mechanical
governor's flyweights, which modulate the position of
The description and operating principles of the
the governor fuel bypass valve. Control of fuel flow to
fuel, air, lubrication, and electrical systems, as well as
maintain proper engine discharge temperature is
their components, are discussed in the following text.
provided by action of the acceleration and
overtemperature control thermostat, which bleeds
Fuel System
control air from one side of the fuel scheduling valve's
diaphragm. This causes a reduced fuel pressure to the
The fuel system consists of fuel and pneumatic
fuel atomizer assemblies, thereby reducing turbine
control components and the necessary interconnecting
temperature.
plumbing (fig. 12-16). The main component of the
Anytime the output air switch is selected, the
system is the fuel control assembly (fig. 12-17), which
n o r m a l l y c l o s e d a u x i l i a r y f u e l s o l e n o i d va l ve
incorporates, within one unit, a gear-type pressure
energizes open to permit additional fuel flow for higher
pump, a fuel filter, a relief valve, a mechanical
(flyweight) governor, and a fuel scheduling valve
load requirements.
12-18
