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APU Valves

This document describes three valves and a light related to the pneumatic system of the APU of an aircraft: 1) The APU air purge valve controls the flow of purge air from the APU to the pneumatic system; 2) The APU pressure relief valve vents excess pressure in the pneumatic duct; 3) The APU purge air isolation valve separates or connects the left and right pneumatic systems.

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9 views5 pages

APU Valves

This document describes three valves and a light related to the pneumatic system of the APU of an aircraft: 1) The APU air purge valve controls the flow of purge air from the APU to the pneumatic system; 2) The APU pressure relief valve vents excess pressure in the pneumatic duct; 3) The APU purge air isolation valve separates or connects the left and right pneumatic systems.

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Air purge valve (closure) of the APU

A. The purge air valve of the APU is a modulating valve that

used to control the purge airflow from the APU to the system

aircraft tire.

B. When the APU is operating at 95% or more, the purge air

The APU can be obtained with the switch in the ON position. The

APU air is automatically regulated. This is to ensure that

the maximum purge air of the APU without overloading the APU.

APU pressure relief valve

A. The APU pressure relief valve is a closed regulator with

purge type spring that contains a seat valve and spring. Its

the purpose is to ventilate the excess pressure in the pneumatic duct to

avoid a condition of overpressure that could cause the rupture of

conduct
Air purge isolation valve

A. The purge air isolation valve is installed in the center of the

cross duct to separate the left and right pneumatic systems or

to connect them when necessary. The isolation valve is a

115 volt butterfly valve, single-phase and motor-driven. The

valve normally remains closed unless needed

crossfeed of purge air.

B. The valve is controlled by a three-position switch (OPEN-

AUTO-CLOSED) in the P5 panel. It is electrically connected through

the switches of the left and right packages and also through the

engine purge switches No. 1 and No. 2.

C. With the isolation valve switch in AUTO, the switches of

engine purge in ON and the switches in AUTO or HIGH, the valve of

isolation will remain closed.

D. The other two positions, OPEN and CLOSED, function as a

conventional switch regardless of the positions of the

package switches and purge switch positions.


Double purge light

(Figure 9)

A. The DUAL BLEED light on the upper panel of the P5 pilot indicates that the system

The tire is pressurized by the engines and the APU at the same time.

B. The DUAL BLEED light circuit is completed with the combination of

engine purge switch number 1 ON and the APU purge valve

open. A combination of engine purge switch number 2 in ON, valve

of open isolation and the APU purge valve also open

will complete the circuit


PG---50

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