Chapter 15

2. Chapter 15 Source of Pneumatic Power Compressed-Air Unit and Compressor

3. Objectives • Describe the function of a compressed-air unit. • Name and explain the function of each of the components in a compressed-air unit. • Identify the basic designs used in air compressor construction. • Compare the operating characteristics of positive- and non-positive-displacement air compressors. Permission granted to reproduce for educational use only.

4. Objectives • Compare the operating characteristics of rotary and reciprocating air compressors. • Describe the general construction characteristics of the various compressor types. • Explain the operation of the various systems used to control the maximum air pressure available from the compressed-air unit. Permission granted to reproduce for educational use only.

5. Objectives • Identify the factors that must be considered to estimate the required output of a compressor to meet the air demands of a pneumatic system. • Interpret performance data supplied by a compressor manufacturer. Permission granted to reproduce for educational use only.

6. Compressed-Air Unit • The source of compressed air for a pneumatic system is the compressed-air unit • Prime mover • Compressor • Other components to condition and store the pressurized air used by the system workstations • Compressed air units vary in size Permission granted to reproduce for educational use only.

7. Compressed-Air Unit • Very small packages may produce only a fraction of a cubic foot of air per minute (cfm) DeVilbiss Air Power Company Permission granted to reproduce for educational use only.

8. Compressed-Air Unit • Large, industrial units may produce thousands of cfm Badger Iron Works, Inc. Permission granted to reproduce for educational use only.

9. Compressed-Air Unit • Compressed-air units can be classified as portable units or central air supplies • Physical size is not the only factor in placing a unit in one of these classes • Easy transport of a unit from one location to another is a more important factor • Many portable units have a larger capacity than many stationary central air supplies Permission granted to reproduce for educational use only.

10. Compressed-Air Unit • A portable unit may be large or small Permission granted to reproduce for educational use only.

11. Compressed-Air Unit • Portable units allow the compressor to be moved to the work site Atlas Copco Permission granted to reproduce for educational use only.

12. Compressed-Air Unit • A compressed-air unit consists of: • Prime mover • Compressor • Coupling • Receiver • Capacity-limiting system • Safety valve • Air filter • May have a cooler and dryer Permission granted to reproduce for educational use only.

13. Compressed-Air Unit • The prime mover in a compressed-air unit may be: • Electric motor • Internal combustion engine • Steam or gas turbine • A coupling connects the prime mover to the compressor Permission granted to reproduce for educational use only.

14. Compressed-Air Unit • Belt coupling DeVilbiss Air Power Company Permission granted to reproduce for educational use only.

15. Compressed-Air Unit • Mechanical coupling DeVilbiss Air Power Company Permission granted to reproduce for educational use only.

16. Basic Compressor Design • A variety of designs are used for air compressors in the compressed-air unit • Reciprocating piston • Rotary, sliding vane • Rotary screw • Dynamic Permission granted to reproduce for educational use only.

17. Basic Compressor Design • Reciprocating-piston compressors are the most common • Rotary screw compressors are popular in new installations Permission granted to reproduce for educational use only.

18. Basic Compressor Design • Inline, reciprocating compressor DeVilbiss Air Power Company Permission granted to reproduce for educational use only.

19. Basic Compressor Design • The basic operation of any compressor includes three phases • Air intake • Air compression • Air discharge • Component parts and physical operation varies between compressor designs Permission granted to reproduce for educational use only.

20. Basic Compressor Classifications • Compressors are classified as: • Positive or non-positive displacement • Reciprocating or rotary • Positive-displacement compressors mechanically reduce the compression chamber size to achieved compression • Non-positive-displacement compressors use air velocity to increase pressure Permission granted to reproduce for educational use only.

21. A reciprocating compressor has a positive displacement Basic Compressor Classifications DeVilbiss Air Power Company Permission granted to reproduce for educational use only.

22. Compressor Design and Operation • Reciprocating compressors use a cylinder and a reciprocating piston to achieve compression • Rotary compressors use continuously rotating vanes, screws, or lobed impellers to move and compress the air Permission granted to reproduce for educational use only.

23. Compressor Design and Operation • Reciprocating compressors are commonly used in pneumatic systems • Very small, single-cylinder, portable compressors for consumer use • Large, industrial, stationary units may produce thousands of cubic feet of compressed air per minute Permission granted to reproduce for educational use only.

24. Compressor Design and Operation • Large, industrial, reciprocating compressor Atlas Copco Permission granted to reproduce for educational use only.

25. Compressor Design and Operation • Reciprocating compressors are available in single- or multiple-cylinder designs • Multiple cylinders may be arranged as: • Inline • Opposed • V type • W type • Other cylinder configuration Permission granted to reproduce for educational use only.

26. Inline reciprocating compressor Compressor Design and Operation DeVilbiss Air Power Company Permission granted to reproduce for educational use only.

27. Compressor Design and Operation • V-type reciprocating compressor DeVilbiss Air Power Company Permission granted to reproduce for educational use only.

28. Compressor Design and Operation • Reciprocating compressors use a single-acting or double-acting compression arrangement • Single-acting compressors compress air during one direction of piston travel • Double-acting compressors have two compression chambers, allowing compression on both extension and retraction of the piston Permission granted to reproduce for educational use only.

29. Double-acting compressor Compressor Design and Operation Permission granted to reproduce for educational use only.

30. Compressor Design and Operation • Rotary, sliding-vane compressors use a slotted rotor containing movable vanes to compress air • Rotor is placed off center in a circular compression chamber, allowing the chamber volume to change during rotation • These volume changes allow the intake, compression, and discharge of air during compressor rotation Permission granted to reproduce for educational use only.

31. Compressor Design and Operation • Centrifugal force keeps the vanes in contact with the walls Permission granted to reproduce for educational use only.

32. Compressor Design and Operation • Rotary screw compressors use intermeshing, helical screws to form chambers that move air from the atmosphere into the system on a continuous basis • This produces a nonpulsating flow of air at the desired pressure level Permission granted to reproduce for educational use only.

33. Compressor Design and Operation • Rotary screw compressors have intermeshing, helical screws Atlas Copco Permission granted to reproduce for educational use only.

34. Compressor Design and Operation • Rotary screw compressors have become popular for larger industrial installations • Lower initial cost • Lower maintenance cost • Adaptable to sophisticated electronic control systems Permission granted to reproduce for educational use only.

35. Compressor Design and Operation • Sliding vane and screw compressor designs often inject oil into the airstream moving through the compressors • Reduces wear on vane and screw contact surfaces • Improves the seal between the surfaces • Oil is removed by a separator to provide near-oilless compressed air for the pneumatic system Permission granted to reproduce for educational use only.

36. Compressor Design and Operation • The basic operating theory of dynamic compressors is converting the kinetic energy of high-speed air into pressure • Dynamic compressor designs are either: • Centrifugal • Axial Permission granted to reproduce for educational use only.

37. Compressor Design and Operation • Centrifugal dynamic compressor: • An impeller increases airspeed • Prime mover energy is converted into kinetic energy as airspeed rapidly increases through the impeller • Kinetic energy is converted to air pressure as air movement slows in the volute collector Permission granted to reproduce for educational use only.

38. Centrifugal dynamic compressor Compressor Design and Operation Permission granted to reproduce for educational use only.

39. Impeller assembly of a centrifugal dynamic compressor Compressor Design and Operation Permission granted to reproduce for educational use only.

40. Compressor Design and Operation • Axial-flow dynamic compressor: • Rotating rotor blades increase airspeed • Fixed stator blades decrease airspeed • Kinetic energy is converted to air pressure • Series of rotor and stator sections are staged to form the axial-flow compressor Permission granted to reproduce for educational use only.

41. Compressor Design and Operation • Axial-flow dynamic compressor Permission granted to reproduce for educational use only.

42. Pressure is created when high-speed air is slowed by the fixed stator blades Compressor Design and Operation Permission granted to reproduce for educational use only.

43. Compressor Design and Operation • Dynamic compressor designs are used to compress air and other gases for large, industrial applications • Oil refineries • Chemical plants • Steel mills Permission granted to reproduce for educational use only.

44. Compressor Design and Operation • Lobe-type compressors consist of two impellers with two or three lobes that operate in an elongated chamber in the compressor body • Spinning impellers trap air in chambers that form between the lobes • As the impellers turn, this trapped air is swept from the inlet port to the outlet port to increase system pressure Permission granted to reproduce for educational use only.

45. Compressor Design and Operation • Impellers from a lobe-type compressor Atlas Copco Permission granted to reproduce for educational use only.

46. Compressor Design and Operation • Lobe-type compressors are often called blowers • They are typically used in applications requiring air pressure of only 10 to 20 psi Permission granted to reproduce for educational use only.

47. Compressor Design and Operation • Compressor staging involves connecting a number of basic compressor units in series to raise air pressure in small increments • This method permits easier control of air temperature, which results in more-efficient compressor package operation Permission granted to reproduce for educational use only.

48. Compressor Design and Operation • Inline, staged, reciprocating compressor DeVilbiss Air Power Company Permission granted to reproduce for educational use only.

49. Compressor-Capacity Control • Compressor-capacity controlrefers to the system that matches the compressed-air output to the system-air demand • The better the air output of the compressor matches system consumption, the more cost effective the operation of the system Permission granted to reproduce for educational use only.

50. Compressor-Capacity Control • Compressor-capacity control systems include: • Bypass • Start-stop • Inlet valve unloading • Speed variation • Inlet size variation Permission granted to reproduce for educational use only.