1. Intro to Chapter 13
Compressed Air
The Energy Transmitting Medium

2. Objectives Describe the characteristics of free air.
Identify the problems associated with the use of unconditioned air in a pneumatic system.
Compare the composition of compressed air in a pneumatic system with the characteristics of free air.
Explain the terms used to describe characteristics of compressed air.

3. Objectives
Compare the scales used to measure the pressure of free and compressed air.
Compare the isothermal, adiabatic, and actual modes of air compression.
Apply the principles of the general gas law to the compression and expansion of the air used in a pneumatic system.

4. Basic Source of System Air
The source of air used in pneumatic systems is the atmosphere
The atmosphere blankets Earth in a layer of gas approximately 360 miles deep

5. Basic Source of System Air
The atmosphere contains several layers

6. Basic Source of System Air
The four layers in the atmosphere are:
Troposphere
Stratosphere
Mesosphere
Ionosphere
We live in the troposphere, which is approximately 10 miles deep

7. Basic Source of System Air
The gases in atmospheric air are:
Nitrogen (79%)
Oxygen (20%)
Other gases (1%)

8. Basic Source of System Air
Composition of atmospheric air

9. Basic Source of System Air
In addition to gases, the atmosphere contains water vapor and entrapped dirt
Both of these influence air compression and the final quality of the system air

10. Basic Source of System Air
The weight of the gases in the atmosphere exerts pressure
Atmospheric pressure is 14.7 pounds per square inch at sea level
0 psig
14.7 psia

11. Basic Source of System Air
Atmospheric pressure varies by elevation

12. Pneumatic System Compressed Air
Atmospheric air is typically referred to as free air
Free air must be conditioned before it can be used in a pneumatic system
Certain locations require considerable preparation of free air to make it usable in a pneumatic system

13. Pneumatic System Compressed Air
Free air at construction sites often requires extra filtration
Manufactured Housing Institute

14. Pneumatic System Compressed Air
Quarrying operations are very dusty
Atlas Copco

15. Pneumatic System Compressed Air
The conditioning of compressed air for use in pneumatic systems involves:
Removal of entrapped dirt
Removal of water vapor
Removal of heat
Incorporation of lubricants

16. Pneumatic System Compressed Air
The amount of water vapor air can hold depends on the temperature of the air
The higher the temperature, the greater the amount of water that can be retained by the air
Saturation is reached when air holds the maximum amount of water for the given temperature

17. Pneumatic System Compressed Air
Water legs are used to collect and remove liquid water from pneumatic lines

18. Pneumatic System Compressed Air
Relative humidity expresses the percentage of water in the air compared to the maximum amount that can be held at the specified temperature
Dew point is the temperature at which water vapor in the saturated air begins to be released in liquid form

19. Pneumatic System Compressed Air
At the dew point, any increase in humidity is released as liquid water, as on a fogged mirror

20. Pneumatic System Compressed Air
Dry compressed air contains water vapor, but the relative humidity is sufficiently low to prevent the formation of liquid water at the ambient temperature of the workstation

21. Pneumatic System Compressed Air
A lubricant is added to dry compressed air distributed by the pneumatic system workstation
This is for protection of system components

22. Pneumatic System Compressed Air
A lubricator for a pneumatic workstation

23. Compression and Expansion of Air
In an operating pneumatic system, the continuous interaction of temperature, pressure, and volume changes make calculations complex

24. Compression and Expansion of Air
Two compression models are used to express air compression
Isothermal compression
Adiabatic compression
These models are used for expansion as well

25. Compression and Expansion of Air
Isothermal compression assumes that all heat is removed, resulting in a constant temperature
Adiabatic compression assumes all heat is retained, resulting in both increased temperature and pressure
Actual compression is somewhere between isothermal and adiabatic compression

26. Compression and Expansion of Air
Comparison of compression models

27. Reaction of Air to Temperature, Pressure, and Volume
Any change in air pressure results in temperature or volume changes

28. Reaction of Air to Temperature, Pressure, and Volume
Changes in the volume of air result in pressure or temperature changes

29. Reaction of Air to Temperature, Pressure, and Volume
Increases or decreases in air temperature result in pressure or volume changes

30. Reaction of Air to Temperature, Pressure, and Volume
Engineering data are available from component manufacturers and data handbooks that can be used to estimate performance from compressors and other system components

31. Reaction of Air to Temperature, Pressure, and Volume
When air is compressed, there are changes in temperature, pressure, and volume that follow the relationships expressed by the general gas law
Local atmospheric Pressure in psi
Local atmospheric Pressure in Pa

32. = volume
Gay-Lussac’s Law
Charle’s Law
Boyle’s Law

34. Standard air condition
Pressure = 14.7 psia =101 kPa abs
Temperature = 68 oF= 20 oC
Relative humidity = 36%

35. US customary system
SI system

36. Review Question
The air we breath and use as the source of air for pneumatic systems contains several gases. Name the gases and indicate the percentage at which they exist in the atmosphere.
A. Nitrogen 79%, B. oxygen 20%, and C. other gases 1% (includes argon, ozone, and carbon dioxide)

37. Review Question
The atmosphere blankets Earth with a layer of gases approximately _____ miles deep.
360

38. Review Question
_____ refers to the amount of water vapor actually carried by a volume of air compared to the maximum amount it can carry at the specified temperature.
Relative humidity

39. Review Question
Standard atmospheric pressure is _____ psia at sea level.
14.7

40. Review Question Define saturation.
The point where the maximum amount of water is held by air for a given temperature.

41. Review Question
The process that assumes all heat is retained in the air during compression is known as _____ compression.
adiabatic

42. Review Question
According to the general gas law, what happens when the pressure of air is changed?
Temperature and/or volume also changes.