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Pneumatics
101
PERFECT
GAS LAWS
Because
pneumatics involves gases, the laws that govern gases are very important.
The "Perfect Gas Laws" express the relationships between pressure, volume,
and temperature. When applying these laws, remember that only absolute
values of pressure and temperature can be used.
1)
Boyle's Law - This law expresses the relationship between pressure and
volume when temperature is held constant. According to Boyle's Law, the
volume of gas in a container is inversely proportional to the absolute
pressure on the gas. Or,
P1V1
= P2V2
The
equation above is correct only after the compressed gas has been allowed
to cool to the temperature it was before the compression took place. Remember,
Boyle's Law applies when temperature is held constant.
2)
Charles' Law - This law expresses the relationship between volume and
temperature when pressure is held constant. According to Charles' Law,
the volume of gas in an expendable container is directly proportional
to the absolute temperature. Or,
V1T2
= V2T1
3)
Gay-Lussac's Law - This law states that if the volume of a gas is held
constant (i.e., confined in a rigid container), the absolute pressure
of the gas is directly proportional to its absolute temperature. Or,
P1T2
= P2T1
For
example, if a closed container is heated, the internal pressure goes up,
and eventually the container may even explode.
These
three gas laws can be combined into a single gas law. The General Gas
Law is expressed by the following equation:
P1V1T2=
P2V2T1
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