to full speed, the fuel is probably not flowing properly
acceleration and overtemperature thermostat is set too
through the fuel atomizers. Check the atomizer screens
low or the load control thermostat is set too high.
and discharge patterns for foreign contamination or a
Check the auxiliary fuel shutoff valve. See if the
carbon buildup on the atomizer tip.
pneumatic shutoff valve is stuck open. Check the
control air pressure plumbing and connections for
Engine Shuts Down Intermittently For No
leaks. All of these conditions can affect the fuel control
Apparent Reason
governor's ability to provide the proper fuel pressure
under load. If all components mentioned are within
The engine stops any time its fuel supply is
specification, replace the fuel control.
interrupted long enough for the residual flame in the
In rare circumstances, too much droop could be the
combustion chamber to go out. Poor electrical contact
result of more applied load than the unit was designed
in the oil pressure switch can cause cycling of the fuel
to handle or an internal mechanical malfunction, such
solenoid valve, thus interrupting fuel flow to the
as rubbing parts or defective bearings.
combustion chambers. Also, bouncing contacts in the
110-percent switch (overspeed) can cause cycling of
TROUBLESHOOTING AND
the fuel shutoff and drain solenoid valve and still leave
MAINTENANCE AIDS
the electrical system holding coil energized. If
shutdown occurs from any of these conditions, fuel
The engine and its components can almost always
will continue to be atomized into the combustion
b e c h e c ke d w i t h o u t r e m ova l f r o m t h e s e r v i c e
chamber during deceleration of the unit and a "fog" of
installation (skid, trailer, enclosure, etc.) by using a
unburned fuel may be emitted from the turbine
special test panel, such as the UPUA4-1 gas turbine
engine analyzer, to provide the necessary controls and
I f n o ev i d e n c e o f f o g g i n g i s s e e n d u r i n g
instrumentations. If the engine is being test run outside
deceleration following an unscheduled shutdown, it is
the service installation, a special test stand, such as the
l i ke l y t h a t t h e e l e c t r i c a l c o n t r o l s h ave b e e n
UTTS-1-7 test stand, is used.
de-energized and that the fuel shutoff and drain
solenoid valve is closed. The 110-percent switch
Gas Turbine Engine Test Stand
should be suspected now, as it may be set too low.
The UTTS-1-7 (fig. 12-25) is a universal test stand
A sharp rap on the switch housing assembly with
for checking gas turbine engines normally found in
the plastic handle of a screwdriver while the unit is
support equipment. The test stand provides engine
running may be tried to check the 110-percent switch.
support, a source of electrical power, fuel, and oil. The
If the "rap" causes the contacts to open and shut down
gas turbine engine analyzer must be used with this test
the engine, it is obvious the switch is off. If the unit
stand to provide the necessary controls and test
does not stop, check the main electrical control relay
instrumentation. The analyzer is shown installed on the
for intermittent operation.
test stand in figure 12-25.
Excessive Speed (RPM) Droop When Load is
Because the test stand is adaptable to many
Applied
different engines, it may be necessary to procure
adapter assemblies (special tools) required for
Normally, the speed need not decrease more than 2
mounting a specific engine into the test stand. The
percent to provide enough signal for the fuel control
technical manual for the test stand lists all of the
mechanical governor to produce sufficient fuel
required parts, plus the instructions for mounting the
pressure to force the required flow through the fuel
engine in the stand.
atomizer for full load. Excessive droop upon load
application is a result of the fuel system's failure to
Gas Turbine Engine Maintenance Stand
provide the increased pressure required, or the
inability of the turbine to convert the power that it
The 281270-0-3 gas turbine engine portable
receives efficiently.
maintenance stand (fig. 12-26) is used when the engine
is removed from the service installation and
If this condition occurs, make the following
components are removed for replacement of the engine
checks. Check to see if the boost pump is operating
or for aiding periodic maintenance. This maintenance
properly. Check to see if the primary and secondary
fuel filters are clogged or collapsed. Check to see if the
stand is well suited for the shipboard environment
12-32
