Vacuum System

Por: Stiven Pinzon

Vacuum Pressure

Gyro pressure gauge, vacuum gauge, or

suction gauge are all terms for the same gauge

used to monitor the vacuum developed in the

system that actuates the air driven gyroscopic

flight instruments.

In some aircraft, all the gyros are vacuum,

pressure, or electrically operated.

while the electrical system provides the power

for the turn coordinator.

The vacuum or pressure

system spins the gyro by

drawing a stream of air

against the rotor vanes to

spin the rotor at high

speed, much like the

operation of a

waterwheel or turbine.

The amount of vacuum or pressure required

for instrument operation varies, but is usually

between 4.5 “Hg and 5.5 “Hg.

one source of vacuum

for the gyros is a vane-

type engine-driven pump

that is mounted on the

accessory case of the

engine. Pump capacity

varies in different

airplanes, depending on

the number of gyros.

Shaft

rotor

case

Vane

InletOulet

typical vacuum system consists of an engine-

driven vacuum pump, relief valve, air filter,

gauge, and tubing necessary to complete the

connections. The gauge is mounted in the

aircraft’s instrument panel and indicates the

amount of pressure in the system (vacuum is

measured in inches of mercury less than

ambient pressure).

Operation

air is drawn into the vacuum system by the

engine-driven vacuum pump. It first goes through

a filter, which prevents foreign matter from

entering the vacuum or pressure system. The air

then moves through the attitude and heading

indicators, where it causes the gyros to spin. A

relief valve prevents the vacuum pressure, or

suction, from exceeding prescribed limits. After

that, the air is expelled overboard or used in other

systems, such as for inflating pneumatic deicing

boots.

Important

To monitor vacuum pressure during flight,

because the attitude and heading indicators

may not provide reliable information when

suction pressure is low.

Some aircraft are equipped with a warning

light that illuminates when the vacuum

pressure drops below the acceptable level.

Mal funcionamiento

When the vacuum pressure drops below the

normal operating range, the gyroscopic

instruments may become unstable and

inaccurate. Checking the instruments

routinely is a good habit to develop.