SSPU control module assembly. The warning light
The air shutoff valve is opened to direct air to the fuel
nozzle assembly to assist in fuel atomization. The valve
alerts the operator to the icing condition. The
remains open until the 95 percent turbine speed switch
operator then places the DE-ICING switch located
de-energizes the air compressor, then the valve closes.
on the SSPU wash and de-icing module assembly
in the ON position. This switch energizes the
The air compressor switch closes when air
de-icing bleed air valve OPEN, directing
compressor pressure is 7 psi. This allows the fuel shutoff
valve to open and the fuel nozzle drain valve to close
compressor discharge pressure to the spray tubes in
and lock in the circuit.
compressor discharge pressure raises the inlet air
WATER WASH SYSTEM
temperature. When icing conditions no longer
exist, the thermal switch opens and the BLEED
The water wash system removes salt deposits from
AIR REQUIRED warning light extinguishes. The
the compressor's internal parts. The system sprays wash
operator then positions the DE-ICING switch to
water solution into the compressor turbine plenum. The
OFF, closing the de-icing bleed air valve.
used solution is then expelled from the exhaust. As
The de-icing bleed air valve is spring-loaded closed
on the SSPU. The wash water solution is supplied from
and electrically actuated open. When placed in the ON
a ship shore connection at a pressure of 30 psi. A
position, the DE-ICING switch on the EOS wash and
ship-mounted water shutoff valve is located next to the
de-icing module assembly sends a 24-volt dc signal to
SSPU. The wash switch, located in the EOS, controls
open the de-icing bleed air valve. When the valve opens,
the water shutoff valve.
the compressor discharge pressure is directed to the
The water spray nozzle is mounted in the turbine
ship's air inlet demisters to start the de-icing process in
inlet plenum. It consists of an orifice and a whirl plate.
the air inlet ducts.
This design generates a turbulence within a whirl
Now that you have read about the Garrett SSPU
chamber, causing water wash solution to spray into the
found on the PHM-class ships, let's look at the
compressor inlet. The flow rate through the nozzle is 3.5
Sunstrand T-62T-40-7 auxiliary power unit (APU)
gallons per minute at 30 psi inlet pressure.
found on the LCACs. In chapter 6, you were given an
To operate the wash system, place the wash switch
overview of this prime mover. In the following section,
in the ON position. This opens the water shutoff valve
we will present additional information that you, the
and deactivates the fuel and ignition systems. Then,
GSM, should be aware of concerning this important
position the START-RUN-STOP switch to the RUN
position to energize the starter. At 20 percent turbine
speed, the ship-mounted water shutoff valve should be
manually opened to allow wash water to flow through
SUNSTRAND T-62 APU
the water spray nozzle. The starter automatically
de-energizes after 60 seconds. When the starter
The T-62T-40-7 APU used on the LCACs is
de-energizes, the water wash switch is positioned to
manufactured by the Sunstrand Corporation. Mounted
OFF. The manually operated water valve is also closed.
both port and starboard on the LCAC-class ships, the
For rinsing, this procedure is repeated using fresh water.
Sunstrand T-62 APU provides electrical power and
Afler the rinse is completed, the SSPU should be
bleed air for main engine starting. In chapter 6, we
operated for 5 minutes.
provided an overview of this APU. In this chapter, we
will take a closer look at this important unit.
BLEED AIR (DE-ICING) SYSTEM
CONSTRUCTION AND DESIGN
The bleed air system prevents icing in the air inlet
ducts. The system works by directing compressor
discharge pressure from the turbine plenum into the
The Sunstrand T-62T-40-7 APU system installed on
ship's air inlet demisters.
the LCAC-class ships consists of two GTGSs, two
GCUs, an electronic sequencing unit (ESU), a relay
At the onset of an icing condition, the thermal
switch closes at 37°F, completing the circuit to the
BLEED AIR REQUIRED warning light located on the
equipment (BITE) annunciator box assemblies.