electromechanical and pneumatic components with
assembly in response to electrical control system
operation.
connecting plumbing and wiring. The principal
components of the system are a fuel pump and control
ACCELERATION STABILIZER AND
unit with solenoid valve, an acceleration stabilizer
ADJUSTABLE ORIFICE ASSEMBLY . -- T h e
solenoid and adjustable orifice assembly, a fuel
acceleration stabilizer and adjustable orifice assembly
atomizer assembly, an acceleration control thermostat,
consists of a normally open solenoid valve and an
a turbine plenum drain check valve, an unloading air
adjustable air bleed installed in the control air line
shutoff valve with solenoid valve, a differential air
between the pneumatic governor and the acceleration
pressure regulator, and a bleed load thermostat.
control thermostat. Its purpose is to control and
stabilize the rate of acceleration by bleeding control air
FUEL PUMP AND CONTROL UNIT.--The
pressure off the air diaphragm of the pneumatic
fuel pump and control unit incorporate the fuel pump, a
governor. Bleeding off a portion of the air pressure
fuel filter, a pneumatic governor (bypass) valve, a fuel
from the air diaphragm causes the valve to bypass more
pressure relief valve, a flyweight-type (mechanical)
fuel, decreasing the rate of acceleration. The solenoid
governor, and a fuel solenoid valve.
is energized (closed) during starting (up to 35 percent
The integral fuel pump is a two-gear, positive
of governed engine rpm) and when the load switch is
displacement pump. The pump housing contains a
actuated, allowing the pneumatic governor to close and
spring loaded, ball-type pressure relief valve which
provide the increased fuel flow required at these times
returns fuel to the pump inlet to relieve excess fuel
to support engine operation.
pressure. The fuel filter, integral with the fuel pump
FUEL ATOMIZER ASSEMBLY.--The fuel
and control unit in a case, filters all fuel passing from
atomizer assembly is a dual orifice type and is mounted
the fuel pump to the fuel control system components.
on the combustion chamber cap assembly. A flow
The filter case is threaded into the pump and control
divider valve directs all fuel at low pressure to the small
unit housing and contains a replaceable micronic filter
orifice, which provides proper atomization of the fuel
element.
during starting. As engine rpm increases and fuel
The pneumatic governor consists of a relief valve
pressure increases, the flow divider valve actuates to
actuated by two diaphragms--one controlled by fuel
permit combined flow to both orifices.
pressure and the other by a combination of spring
ACCELERATION CONTROL THERMO-
pressure and compressor discharge (control) air
S TAT . -- T h e a c c e l e r a t i o n / o v e r t e m p c o n t r o l
pressure. It is called a bypass valve because it is
thermostat is mounted in the engine tail pipe. It
designed to control fuel flow to the atomizer assembly
consists of a spring-loaded, closed, ball relief valve,
by bypassing a portion of the fuel delivered by the fuel
and is actuated by exhaust gas temperature (EGT). It is
pump back to the fuel pump inlet.
connected to the pneumatic governor by a control air
As engine rpm increases and compressor
line. The thermostat acts to override control of fuel
discharge air pressure increases, less fuel is bypassed
flow by dumping some control air pressure from the air
and more is delivered to the atomizer assembly. The
diaphragm of the pneumatic governor if the EGT
pneumatic governor controls fuel flow during starting
exceeds a specified limit during acceleration.
and acceleration up to approximately 95% of governed
TURBINE PLENUM DRAIN CHECK
engine rpm.
VALVE.--The turbine plenum drain check valve is
The mechanical governor begins to function as
located at the bottom of the turbine plenum. It allows
engine rpm reaches approximately 95%. Enough
fuel to drain, except when compressor pressure is built
centrifugal force is applied to the flyweights at this
up in the turbine plenum. The valve purpose is to
point to allow the governor to begin bypassing fuel,
prevent accumulation of unburned fuel in the turbine
and simultaneously, the pneumatic governor bypass
plenum.
relief valve is locked closed by the increased
UNLOADING AIR SHUTOFF VALVE.--The
compressor discharge pressure. The mechanical
unloading air shutoff (load) valve assembly consists of
governor allows just enough fuel to reach the atomizer
a normally closed solenoid valve, a normally closed
assembly to maintain governed engine rpm.
butterfly valve, and two diaphragms. It functions to
The fuel solenoid valve is the normally closed
control the amount of air that is bled from the engine in
relation to EGT. If too much air is being bled off
type. It admits or shuts off fuel flow to the atomizer
12-7
