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Chapter 14

Chapter 14. Compressed Air. The Energy Transmitting Medium. Objectives. Describe the characteristics of free air. Identify the problems associated with the use of unconditioned air in a pneumatic system.

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Chapter 14

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  1. Chapter 14 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. Permission granted to reproduce for educational use only.

  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. Permission granted to reproduce for educational use only.

  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 Permission granted to reproduce for educational use only.

  5. Basic Source of System Air • The atmosphere contains several layers Permission granted to reproduce for educational use only.

  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 Permission granted to reproduce for educational use only.

  7. Basic Source of System Air • The gases in atmospheric air are: • Nitrogen (79%) • Oxygen (20%) • Other gases (1%) Permission granted to reproduce for educational use only.

  8. Basic Source of System Air • Composition of atmospheric air Permission granted to reproduce for educational use only.

  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 Permission granted to reproduce for educational use only.

  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 Permission granted to reproduce for educational use only.

  11. Basic Source of System Air • Atmospheric pressure varies by elevation Permission granted to reproduce for educational use only.

  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 Permission granted to reproduce for educational use only.

  13. Free air at construction sites often requires extra filtration Pneumatic System Compressed Air Manufactured Housing Institute Permission granted to reproduce for educational use only.

  14. Quarrying operations are very dusty Pneumatic System Compressed Air Atlas Copco Permission granted to reproduce for educational use only.

  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 Permission granted to reproduce for educational use only.

  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 Permission granted to reproduce for educational use only.

  17. Water legs are used to collect and remove liquid water from pneumatic lines Pneumatic System Compressed Air Permission granted to reproduce for educational use only.

  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 pointis the temperature at which water vapor in the saturated air begins to be released in liquid form Permission granted to reproduce for educational use only.

  19. Pneumatic System Compressed Air • At the dew point, any increase in humidity is released as liquid water, as on a fogged mirror Permission granted to reproduce for educational use only.

  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 Permission granted to reproduce for educational use only.

  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 Permission granted to reproduce for educational use only.

  22. A lubricator for a pneumatic workstation Pneumatic System Compressed Air Permission granted to reproduce for educational use only.

  23. Compression andExpansion of Air • In an operating pneumatic system, the continuous interaction of temperature, pressure, and volume changes make calculations complex Permission granted to reproduce for educational use only.

  24. Compression andExpansion of Air • Two compression models are used to express air compression • Isothermal compression • Adiabatic compression • These models are used for expansion as well Permission granted to reproduce for educational use only.

  25. Compression andExpansion 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 Permission granted to reproduce for educational use only.

  26. Compression andExpansion of Air • Comparison of compression models Permission granted to reproduce for educational use only.

  27. 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 • (P1  V1)  T1 = (P2  V2)  T2 • Specific system pressure, temperature, and volume changes may be difficult to verify Permission granted to reproduce for educational use only.

  28. Any change in air pressure results in temperature or volume changes Reaction of Air to Temperature, Pressure, and Volume Permission granted to reproduce for educational use only.

  29. Reaction of Air to Temperature, Pressure, and Volume • Changes in the volume of air result in pressure or temperature changes Permission granted to reproduce for educational use only.

  30. Reaction of Air to Temperature, Pressure, and Volume • Increases or decreases in air temperature result in pressure or volume changes Permission granted to reproduce for educational use only.

  31. 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 Permission granted to reproduce for educational use only.

  32. 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) Permission granted to reproduce for educational use only.

  33. Review Question The atmosphere blankets Earth with a layer of gases approximately _____ miles deep. 360 Permission granted to reproduce for educational use only.

  34. 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 Permission granted to reproduce for educational use only.

  35. Review Question Standard atmospheric pressure is _____ psia at sea level. 14.7 Permission granted to reproduce for educational use only.

  36. Review Question Define saturation. The point where the maximum amount of water is held by air for a given temperature. Permission granted to reproduce for educational use only.

  37. Review Question The process that assumes all heat is retained in the air during compression is known as _____ compression. adiabatic Permission granted to reproduce for educational use only.

  38. Review Question According to the general gas law, what happens when the pressure of air is changed? Temperature and/or volume also changes. Permission granted to reproduce for educational use only.

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