1. Pneumatic Power Principles of Engineering
© 2012 Project Lead The Way, Inc.

2. Pneumatic Power Pneumatic power Pneumatics vs. hydraulics
Early pneumatic uses
Properties of gases
Pascal’s Law
Perfect gas laws
Boyle’s Law
Charles’ Law
Gay-Lussac’s Law
Common pneumatic system components
Compressor types
Future pneumatic possibilities

3. Pneumatic Power Pneumatics
The use of a gas flowing under pressure to transmit power from one location to another
Gas in a pneumatic system behaves like a spring since it is compressible.
Air is most commonly used in pneumatic systems, although some systems use nitrogen. Pure nitrogen may be used if there is a danger of combustion in a work environment.

4. Pneumatics vs. Hydraulics
Pneumatic Systems . . .
Use a compressible gas
Possess a quicker, jumpier motion
Are not as precise
Require a lubricant
Are generally cleaner
Often operate at pressures around 100 psi
Generally produce less power

5. Early Pneumatic Uses Bellows
Tool used by blacksmiths and smelters for working iron and other metals

6. Early Pneumatic Uses Otto von Guericke
Showed that a vacuum can be created
Created hemispheres held together by atmospheric pressure
Von Guericke held public demonstrations in Germany during the 1660s where teams of horses tried to pull apart hemispheres held together by atmospheric pressure created using a pump.

7. Early Pneumatic Uses America’s First Subway Designed by Alfred Beach
Built in New York City
Completed in 1870
312 feet long, 8 feet in diameter
Closed in 1873

8. Properties of Gases Gases are affected by 3 variables
Temperature (T)
Pressure (p)
Volume (V)
Gases have no definite volume
Gases are highly compressible
Gases are lighter than liquids

9. Properties of Gases Absolute Pressure
Gauge Pressure: Pressure on a gauge does not account for atmospheric pressure on all sides of the system
Absolute Pressure: Atmospheric pressure plus gauge pressure
Absolute pressure is used to complete pneumatic calculations.
Atmospheric pressure is also known as barometric pressure. It is the weight of the air molecules. An application of air pressure is when your ears pop. The pressure is balancing on the inside and outside of your ear.
Gauge Pressure + Atmospheric Pressure = Absolute Pressure

10. Properties of Gases Absolute Pressure
Pressure (p) is measured in pounds per square inch (lb/in.2 or psi)
Standard atmospheric pressure equals 14.7 lb/in.2
If a gauge reads psi, what is the absolute pressure?
120.0 lb/in lb/in.2 = lb/in.2
Atmospheric pressure equals 14.7 psi at sea level. Atmospheric pressure is lower at higher elevations because less air exists above to exert pressure. Similarly, atmospheric pressure is higher at elevations lower than sea level.
A note of caution: reported pressure from weather stations are referenced to the usual pressure in that location. The reported pressure is called the “station pressure”, and is corrected for elevation- so the station pressure at the highest human settlements would be around 30 inches of mercury (=14.7 psi) while the actual barometric pressure is less than 7.0 psi.

11. Properties of Gases Absolute Temperature
0°F does not represent a true 0°
Absolute Zero = -460.°F
Absolute Temperature is measured in degrees Rankine (°R)
°R = °F
True 0° represents the lack of molecular movement. Molecular movement increases as temperature increases.
Pneumatics equations should use absolute temperature.
If the temperature of the air in a system is 65 °F, what is the absolute temperature?
Answer:
65 °F = 525 °R

12. Pascal’s Law
Pressure exerted by a confined fluid acts undiminished equally in all directions.
Pressure: The force per unit area exerted by a fluid against a surface
Symbol
Definition
Example Unit p
Pressure
lb/in.2 F
Force lb A
Area
in.2
The area of a cylinder will be the surface area of the piston.

13. Pascal’s Law Example
How much pressure can be produced with a 3.00 in. diameter (d) cylinder and 60.0 lb of force (F)?
d = 3.00 in. p = ?
F = 60.0 lb A = ?
Formula p= F A
Formula A=π r 2
Sub / Solve A=π (1.50) 2
Sub / Solve p= 60.0 lb 7.07 in.2
*A=7.07 in. 2
*Note: This intermediate value has been rounded. The full stored value in your calculator should be utilized when substituted into the next step.
Sub / Solve p=8.49 lb in.2

14. Perfect Gas Laws
The perfect gas laws describe the behavior of pneumatic systems
Boyle’s Law
Charles’ Law
Gay-Lussac’s Law

15. Boyle’s Law
The volume of a gas at constant temperature varies inversely with the pressure exerted on it.
NASA
p1 (V1) = p2 (V2)
Symbol
Definition
Example Unit V
Volume
in.3

16. Boyle’s Law Example
A cylinder is filled with 40. in.3 of air at a pressure of 60. psi. The cylinder is compressed to 10. in.3. What is the resulting absolute pressure?
p1 = 60. lb/in.2 V1 = 40. in.3
p2 = ? V2 = 10. in.3
Convert p1 to absolute pressure.
p1 = 60. lb/in lb/in.2 = 74.7 lb/in.2

17. Charles’ Law
Volume of gas increases or decreases as the temperature increases or decreases, provided the amount of gas and pressure remain constant.
NASA
Note: T1 and T2 refer to absolute temperature.

18. Charles' Law Example
An expandable container is filled with 28 in.3 of air and is sitting in ice water that is 32°F. The container is removed from the icy water and is heated to 200.°F. What is the resulting volume?
V1 = 28in.3
V2 = ?
T1 = 32°F
T2 = 200.°F
Convert T to absolute temperature.
T1 = 32°F °F =492°R
T2 = 200.°F °F =660°R
The temperature readings must be converted to absolute temperature in order for the equation to work.

19. Charles' Law Example
An expandable container is filled with 28 in.3 of air and is sitting in ice water that is 32°F. The container is removed from the icy water and is heated to 200°F. What is the resulting volume?
V1 = 28in.3
V2 = ?
T1 = 32°F
T2 = 200.°F
Convert T to absolute temperature
T1 = 32°F °F = 492°R
T2 = 200°F °F = 660°R

20. Gay-Lussac’s Law
Absolute pressure of a gas increases or decreases as the temperature increases or decreases, provided the amount of gas and the volume remain constant.
Note: T1 and T2 refer to absolute temperature.
p1 and p2 refer to absolute pressure.

21. Gay-Lussac’s Law Example
A 300. in.3 sealed air tank is sitting outside. In the morning the temperature inside the tank is 62°F, and the pressure gauge reads 120. lb/in.2. By afternoon the temperature inside the tank is expected to be close to 90.°F. What will the absolute pressure be at that point?
V = 300. in.3 T1 = 62°F
p1 = 120. lb/in.2 T2 = 90.°F
p2 = ?
Convert p to absolute pressure.
p1= 120. lb/in lb/in.2
= lb/in.2
Convert T to absolute temperature.
T1 = 62°F °F = 522°R
T2 = 90.°F °F = 550.°R

22. Gay-Lussac’s Law Example
A 300 in.3 sealed air tank is sitting outside. In the morning the temperature inside the tank is 62°F, and the pressure gauge reads 120 lb/in2. By afternoon the temperature inside the tank is expected to be closer to 90°F. What will the absolute pressure be at that point?
If the absolute pressure is lb/in.2, what is the pressure reading at the gauge?
141.9 lb/in.2 – 14.7 lb/in.2 = lb/in.2
= 130 lb/in.2

23. Common Pneumatic System Components
Transmission Lines
Regulator
Filter
Drain
Directional Control Valve
Receiver Tank
Compressor: Compresses air into the receiver tank.
Pressure Relief Valve: Limits the maximum pressure in the system. It is a safety device that will allow excess pressure to escape to prevent damaging components in the circuit.
Receiver Tank: A device that holds the air in a pneumatic system.
Transmission Lines: Used to transport fluid in a circuit.
Directional Control Valve: Used to control which path a fluid takes in a circuit.
Cylinder: Also called an actuator. Used to convert fluid power to linear mechanical power.
Drain: Removes moisture from the system.
Regulator: A valve used to control pressure in the branch of a circuit.
Filter: Used to remove contamination from fluids. Filters are also often next to lubricators. Lubrication helps prevent wear on the components in the system.
All systems also require seals and gaskets between components to improve the air-tight nature of the system.
Pressure Relief Valve
Cylinder
Compressor
National Fluid Power Association & Fluid Power Distributors Association

24. Reciprocating Piston Compressor
Compressor Types
Reciprocating piston compressors are most common for use in small to medium sized commercial applications. On a two-stage piston compressor, air is drawn into the first stage piston to be compressed and is then sent to the second stage piston where it is further compressed before being sent to the receiver tank.
Compair
Reciprocating Piston Compressor

25. Rotary Screw Compressor
Compressor Types
The rotary screw compressor compresses air between two intermeshing screws.
Compair
Rotary Screw Compressor

26. Rotary Vane Compressor Types Compair
During rotation, centrifugal force extends the vanes from their slots, forming individual compression cells. Rotation decreases volume, increasing the air pressure.
Rotary vane compressors are useful where high capacity is needed. They rotate at very high speeds.
Compair
Rotary Vane

27. Future Pneumatic Possibilities
What possibilities may be on the horizon for pneumatic power?
Could it be human transport?
zapatopi.net

28. Image Resources
Compair. (2008). Compressed air explained: The three types of compressors. Retrieved March 5, 2008, from Explained--03The_three_types_of_compressors.aspx
Johnson, J.L. (2002). Introduction to fluid power. United States: Thomson Learning, Inc.
Microsoft, Inc. (2008). Clip Art. Retrieved January 10, 2008, from
National Aeronautics and Space Administration. (2008). Boyle’s law. Retrieved February 3, 2008, from
National Fluid Power Association. (2008). What is fluid power. Retrieved February 15, 2008, from WhatIsFluidPower.asp
National Fluid Power Association & Fluid Power Distributors Association. (n.d.). Fluid power: The active partner in motion control technology. [Brochure]. Milwaukee, WI: Author.
Zapato, L. (n.d.) The inteli-tube pneumatic transportation system. Retrieved February 29, 2008, from