the wash is complete, the GTE is usually started and run
Two other valves that work hand-in-hand with the
for approximately 5 minutes to dry out the engine.
fifth- and tenth-stage bleed air valves are the
three-way bleed air control valve and the speed
sensitive valve.
TESTS AND INSPECTIONS
THREE-WAY BLEED AIR CONTROL
VALVE. The three-way control valve is used to
Many tests and inspections that are routinely
port fourteenth-stage bleed air to the fifth- and
accomplished are covered by the PMS or
tenth-stage bleed air valves. The air holds these
manufacturer's technical manuals. As part of your
valves closed at engine speeds above 12,780 rpm.
responsibilities for troubleshcmting and inspecting the
GTE, you must also be knowledgeable of borescoping.
The three-way control valve also ports ship's
We will discuss borescoping later in this chapter.
service air to hold these valves closed during an
enclosure fire stop sequence. Your maintenance of
In the following paragraphs, we will confine our
the three-way bleed air control valve will consist
discussion to the tests and inspections you will be
of tests and inspections through routine PMS and
required to perform for specific components and various
in conjunction with safety checks.
parts of your GTE. After we look at the individual
components, we will take a look at the GTE and your
SPEED SENSITIVE VALVE ASSEMBLY. The
responsibilities for borescoping.
speed sensitive valve is the controller (brain) for the
bleed air system. It is attached to and driven by the
accessory gearbox. When engine speed is below
Compressor
12,780 rpm, the valve activates to vent the bleed air
received from the diffuser (fourteenth-stage air) to the
The compressor contains several pieces of
atmosphere, thereby allowing the engine's internal air
equipment that will require maintenance much more
pressure to push open the bleed air valves. When
frequently than the compressor itself. Most of the
engine speed exceeds 12,780 rpm, the air is ported
internal maintenance for a compressor will be
through a filter to the bleed air valves to hold them
accomplished at a naval air depot (NADEP) or shore
closed.
intermediate maintenance activity (SIMA).
Your main responsibility for this system is to keep
Unless you are assigned to a SIMA, the only
the filter located between the speed sensitive valve and
maintenance procedure that you, the GSM, will likely
the bleed air valves clean. The filter is a cleanable mesh
perform on the compressor is cleaning. In the following
type that is consistently exposed to salt, dirt, and
paragraphs, let's take a look at your responsibilities for
moisture. If this filter is not kept clean, the system may
cleaning and maintaining the various components
end up with sufficient air pressure to hold the fifth-stage
associated with the compressor.
bleed air valves closed but not enough to hold the
BLEED AIR VALVES. On the Allison GTE, the
tenth-stage valves closed. If the filter becomes
fifth- and tenth-stage bleed air valves are used to prevent
completely blocked, both sets of valves will remain
compressor stalls during engine start up. Your
open, creating excess air pressure in the engine
maintenance of these valves will be basically limited to
enclosure and increasing the chances of a compressor
cleaning the screens and visually inspecting the
stall.
wire-braid hoses for proper operation during starts, fire
stops, and water washing.
CUSTOMER BLEED AIR VALVE. Although it
is installed in the Allison, Garrett, and Sunstrand
START AIR BYPASS VALVE. Much like the
systems, the customer bleed air valve serves a different
Allison's fifth- and tenth-stage bleed air valves, the
function on each GTE.
Sunstrand uses the start air bypass valve to prevent
compressor surge (stall) during starting. Your
Allison. The Allison's bleed air valve is installed in
maintenance for the Sunstrand's valve will be similar to
the enclosure on the base. It provides bleed air to the
that for the Allison's fifth- and tenth-stage bleed air
entire bleed air system. This air is used for SSGTG and
valves. In both cases, your responsibilities will be
GTM starting, prairie air, masker air, and anti-icing air.
limited to visual inspections and checking for proper
While the valve is supplying bleed air, it works
operation during starts.
automatically to regulate TIT to keep it below the high
TIT alarm set point.
