1. HYDRAULICS & PNEUMATICS
Compressed Air
Source of Pneumatic Power
Presented by: Dr. Abootorabi

2. Basic Source of System Air
The source of air used in pneumatic systems is the atmosphere.
The gases in atmospheric air are:
Nitrogen (79%)
Oxygen (20%)
Other gases (1%)

3. Basic Source of System Air
Composition of atmospheric air

4. 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.
The weight of the gases in the atmosphere exerts pressure.
Atmospheric pressure is 14.7 pounds per square inch at sea level.

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

6. 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.

7. 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

8. 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

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

10. 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.

11. 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.
A lubricant is added to dry compressed air distributed by the pneumatic system workstation. This is for protection of system components.

12. Pneumatic System Compressed Air
A lubricator for a pneumatic workstation:

13. Compression and Expansion of Air
In an operating pneumatic system, the continuous interaction of temperature, pressure, and volume changes make calculations complex.
Engineering data are available from component manufacturers and data handbooks that can be used to estimate performance from compressors and other system components.

14. 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

15. 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.

16. Compressed-Air Unit
Very small packages may produce only a fraction of a cubic foot of air per minute (cfm).
1 ft3 ≈ m3

17. Compressed-Air Unit
Large, industrial units may produce thousands of cfm.

18. 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

19. Compressed-Air Unit
A portable unit may be large or small.

20. Compressed-Air Unit
Portable units allow the compressor to be moved to the work site.

21. 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

22. 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

23. Compressed-Air Unit
Belt coupling:
DeVilbiss Air Power Company

24. Compressed-Air Unit
Mechanical coupling:
DeVilbiss Air Power Company

25. 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

26. Basic Compressor Design
Reciprocating-piston compressors are the most common.
Rotary screw compressors are popular in new installations.

27. 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.

28. 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.

29. Basic Compressor Classifications
A reciprocating compressor has a positive displacement.
DeVilbiss Air Power Company

30. 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.

31. 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

32. Compressor Design and Operation
Large, industrial, reciprocating compressor:
Atlas Copco

33. 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

34. Compressor Design and Operation
Double-acting compressor

35. Compressor Design and Operation
Multiple cylinders may be arranged as:
Inline
Opposed
V type
W type
Other cylinder configuration

36. Compressor Design and Operation
Inline reciprocating compressor:

37. Compressor Design and Operation
V-type reciprocating compressor:

38. 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

39. Compressor Design and Operation
Centrifugal force keeps the vanes in contact with the walls

40. 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.

41. Compressor Design and Operation
Rotary screw compressors have intermeshing, helical screws:

42. 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

43. 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.

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

45. Compressor Design and Operation
Impellers from a lobe-type compressor.

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.

47. 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

48. Compressor Design and Operation
Centrifugal dynamic compressor:
An impeller increases airspeed
Prime mover energy is converted into kinetic energy as air speed rapidly increases through the impeller
Kinetic energy is converted to air pressure as air movement slows in the volute collector

49. Compressor Design and Operation
Centrifugal dynamic compressor:

50. 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

51. Compressor Design and Operation
Axial-flow dynamic compressor:

52. Compressor Design and Operation
Axial-flow dynamic compressor:

53. Compressor Design and Operation
Pressure is created when high-speed air is slowed by the fixed stator blades.

54. 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

55. 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.

56. Compressor Design and Operation
Inline, staged, reciprocating compressor:

57. Compressor-Capacity Control
Compressor-capacity control refers 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.

58. Compressor-Capacity Control
Compressor-capacity control systems include:
Bypass
Start-stop
Inlet valve unloading
Speed variation
Inlet size variation

59. Compressor-Capacity Control
Bypass control uses a relief-type valve to exhaust excess air.
Air is continuously delivered to the system at the compressor’s maximum flow rate.
This type of control is not considered desirable as it is inefficient.

60. Compressor-Capacity Control
Start-stop capacity control is commonly used with small, electric motor-driven compressor packages that operate pneumatic systems consuming air on an intermittent basis.

61. Compressor-Capacity Control
Start-stop control uses a pressure-sensitive switch to start and stop the compressor to maintain a preselected pressure range.

62. Compressor-Capacity Control
Start-stop control: compressor start

63. Compressor-Capacity Control
Start-stop control: compressor stop

64. Compressor-Capacity Control
Inlet valve unloading controls compressor output by holding the inlet valve open whenever maximum system pressure is achieved:
Allows the prime mover to operate continuously
Can be used in systems having internal combustion engines or electric motors as the prime mover

65. Compressor-Capacity Control
Varying compressor speed can control compressor capacity:
Can be used with reciprocating and rotary compressor designs
Primarily used on large, industrial installations
Sensors monitor pressure and send a signal to control compressor speed

66. Compressor-Capacity Control
Varying the size of the compressor inlet can control compressor capacity:
Compressor operates at a constant speed
The volume of air that can enter the compressor is restricted
Output varies with the size of the inlet
Primarily used on dynamic compressors

67. Selecting a Compressor Package
Establishing the level of system air consumption is a key factor when selecting a compressor
This can be accomplished by identifying:
Actuators used in the system
Compressed-air needs of each item
Percentage of time each functions

68. Selecting a Compressor Package
Other factors must be considered during system compressor selection:
Compressor and prime mover type
Method of compressor-capacity control
Auxiliary controls such as coolers, separators, and driers
System instrumentation

69. The end.