GENERAL
The pneumatic system provides air for cabin pressurization, air conditioning, airfoil anti-ice, engine starting, and potable water tank pressurization. It consists of a left and right system which operate independently and can be interconnected to provide a common pressure source. Engine bleed air is the pressure source for all flight operations and can be used on the ground. The auxiliary power unit (APU) can be used to supply pressure to either or both systems during ground operation.
PNEUMATIC DISTRIBUTION
The distribution system consists of left, right, and crossfeed manifold. Crossfeed valves connect the left and right section to the crossfeed manifold. The respective valve must be open to operate air conditioning or engine starting from the APU. When both crossfeed valves are closed, the left engine provides air to the left air conditioning system, the right engine provides air to the right air conditioning system, and the crossfeed manifold is isolated from engine bleed air. Airfoil ice protection can be provided from the left, right, or both engines, depending on crossfeed valve position. With both crossfeed valves open, air from an operating engine can be used to start the opposite engine.
A pneumatic pressure indicator indicates pressure in the crossfeed manifold.
PNEUMATIC CROSSFEED VALVE
The left and right crossfeed valves are mechanically operated. They are normally controlled by their respective pneumatic crossfeed valve lever on the aft pedestal. When the lever is full forward, indicated by a PNEU X-FEED VALVE OPEN placard, its valve is open. With the lever aft, its valve is closed.
The crossfeed valves are also closed by their respective fire control. When a fire control handle is pulled, the respective crossfeed valve closes and the corresponding lever moves to the closed position. The action is reversible; opening the crossfeed lever moves the fire control to the stowed position.
AUGMENTATION VALVE
An augmentation valve for each engine can be armed to regulate the flow of high pressure air into the pneumatic system when low pressure air is not sufficient. High pressure air can augment pressure for the air conditioning system and/or temperature for the airfoil anti-ice system.
Supply air switches on the air conditioning panel control pressure augmentation. In OFF or HP BLD OFF, pressure augmentation is disarmed. In AUTO, the augmentation valve is armed to open for pressure demands. Temperature augmentation for the two-switch airfoil anti-ice system is armed by placing the respective switch ON. For temperature augmentation on the one-switch airfoil anti-ice system, the switch mist be on and the respective crossfeed lever open.
APU AIR
APU air is normally only used for engine starting and ground air conditioning. APU air is controlled by the APU air switch. When the switch is ON or AIR COND COLDER, the APU load control valve opens to provide air to the aircraft pneumatic system. The APU must be operating for one minute before the air switch will open the load control valve. In OFF, the valve is closed. The switch must be off for all flight operations.
PNEUMATIC CONTROLS
LOCATION:
Overhead Panel
SUPPLY AIR SWITCH
OFF - Closes pressure regulator, flow control and augmentation valves. Turns off heat exchanger cooling fan on the ground.
HP BLD OFF - Opens pressure regulator and flow control valves. Disarms pressure augmentation. Turns on heat exchanger cooling fan on
the ground.
AUTO - Opens pressure regulator and flow control valves. Arms augmentation valve to open on demand. Turns on heat exchanger cooling fan
on the ground.
PNEUMATIC PRESSURE INDICATOR
Indicates pressure in the pneumatic crossfeed manifold.
LOCATION:
Aft Pedestal/Trim Panel
PNEUMATIC CROSSFEED VALVE LEVER
Mechanically positions respective pneumatic crossfeed valve in any position from full open (forward) to full closed (aft).
LOCATION:
Overhead Panel
APU AIR SWITCH
AIR OFF - Closes APU load control valve shutting off APU air supply to pneumatic manifold.
ON - Arms the APU load valve to provide air to pneumatic manifold.
AIR COND COLDER - Closes turbine nozzle valve to provide colder APU air supply.
- Indicates that
temperature in the tail compartment is excessive. This could indicate leaks in
the pneumatic ducting.