TM 1-1520-238-T-5
7–8
Change 4
7–2.
LOCATION AND DESCRIPTION OF MAJOR COMPONENTS (cont)
7–2
c. PAS.
The PAS (fig. 7–3) consists of the air particle separator, inlet throttle valve, SDC, surge valve,
temperature sensor, outlet pressure switch, outlet check valve, air pressure manifold, air pressure regulating
valve, bleed air shutoff valve, bleed air check valve, external air receptacle, and the utility air receptacle.
(1) Air Particle Separator.
The air particle separator, located on the upper fuselage fairing frame,
removes 85 percent of the particles 20 microns or larger.
(2) Inlet Throttle Valve.
The inlet throttle valve, located on the upper fuselage fairing frame, reduces
APU starting load.
(3) SDC.
The SDC, located on the rear face of the main transmission accessory section, compresses
and heats air to 30 5 psi at approximately 400 F (204 C).
(4) Surge Valve.
The surge valve, located on the SDC, maintains constant pressure throughout the PAS
system.
(5) Temperature Sensor.
The temperature sensor, located on the SDC, illuminates the SHAFT DRIVEN
COMP indicator on the pilot caution/warning panel when the temperature of the SDC reaches 340 to 360 F
(171 to 182 C). The SHAFT DRIVEN COMP indicator extinguishes when the temperature decreases to 315 to
330 F (157 to 166 C).
(6) Outlet Pressure Switch.
The outlet pressure switch, located on the SDC check valve tube assembly
(between the flexible outlet hose and air pressure manifold), monitors SDC output pressure and controls the
SHAFT DRIVEN COMP indicator on the pilot’s caution/warning panel.
(7) Outlet Check Valve.
The outlet check valve, located on the SDC check valve tube assembly
(between the flexible outlet hose and air pressure manifold), prevents loss of air through the SDC when
secondary or external air is applied
(8) Air Pressure Manifold.
The air pressure manifold, located on the aft equipment bay deck, receives
air from the SDC and distributes it to pneumatic systems and components.
(9) Air Pressure Regulating Valve.
The air pressure regulating valve, located in the aft equipment bay,
regulates PAS air for the fuel system.
(10) Bleed Air Shutoff Valve.
The bleed air shutoff valve, mounted between the engine 1 bleed air input
and the air pressure manifold, allows flow of bleed air upon SDC failure.
(11) Bleed Air Check Valve.
The bleed air check valve, mounted in the air pressure manifold, prevents
primary or external air from entering the bleed air shutoff valve.
(12) External Air Receptacle. The external air receptacle, located on the bottom of the engine 1 nacelle,
provides a connection point for external air via the AGPU.
(13) Utility Air Receptacle.
The utility air receptacle, located in the engine 1 nacelle, provides access for
low pressure power tools and test equipment.
