1-26. The fuel boost pump is an electric motor-driven pump bolted to a support
bracket on the right side of the trailer. The boost pump draws fuel from the fuel tank
and routes it through the fuel filter to the fuel control on the APU. A minimum of 5
psig fuel boost pressure is sufficient to ensure fuel flow to the fuel system of the APU.
1-28. A replaceable-element, low-pressure fuel filter is bolted to a support bracket
on the right side of the trailer. A pressure relief valve within the filter head assembly
is set to relieve at 10 to 12 psig differential pressure. The filter provides lo-micron
filtration of the fuel before entry into the fuel system of the APU.
1-30. The air inlet silencer is a sound suppressor, bolted to thin blocks on the for-
ward left side of the trailer. The silencer consists of a labyrinth-type annular
muffler, lined with acoustical material, a 90-degree adapter elbow, a flexible cou-
pling, and clamps. During engine operation, the air inlet silencer is clamped to the air
inlet shroud of the APU. The labyrinth formed by the insulated silencer assembly re-
duces the noise of intake air to the APU during engine operation.
1 3 2 . The exhaust silencer is a sound suppressor bolted to the frame at the forward
end of the trailer. The silencer consists of a rectangular steel enclosure lined with
acoustical material. The construction of the silencer allows the exhaust gas to expand,
cool, and change direction before leaving the suppressor. A cylindrical inlet tube
telescopes from the silencer and clamps to the exhaust outlet flange of the APU. A
hinged exhaust pipe assembly on the top of the silencer carries the exhaust exit noise
to a height above ear level. A hinged exhaust bypass door on the back of the silencer
ensures safe engine starts in case residual fuel has accumulated at the base of the
silencer, creating an explosive air mixture which could be ignited by the APU exhaust.
1-34. The speed increaser, mounted on a support frame that is bolted to the trailer,
incorporates an axial (straight-through), 6000-rpm pad on which the dc starter-
generator is mounted, and a right-angle, 8000-rpm pad on which the ac generator is
mounted. The APU is mounted on the aft end of the speed increaser, and through the
APU output speed of 6000 rpm, the speed increaser drives the generators at their
respective speeds. The speed increaser is self-contained with an integral oil sump
and a splash oil lubricating system.