Pneumatic Power Topics:

Transcription

1 Pneumatic Power

2 Pneumatic Power Topics: 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.

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.

7 Early Pneumatic Uses America s First Subway Designed by Alfred Beach. Built in New York City. Completed in 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. Gauge Pressure + Atmospheric Pressure = Absolute Pressure

10 Properties of Gases Absolute Pressure Pressure (p) is measured in pounds per square inch (lb/in or psi). Standard atmospheric pressure equals 14.7 lb/in at sea level. If a gauge reads 10.0 psi, what is the absolute pressure? 10.0 lb/in lb/in. = lb/in

11 Properties of Gases Absolute Temperature 0 F does not represent a true 0. Absolute Zero = F Absolute Temperature is measured in degrees Rankine ( R). R = F If the temperature of the air in a system is 65 F, what is the absolute temperature? Answer: 65 F = 55 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 F A p Pressure lb/in. F Force lb A Area in.

13 Pascal s Law Example How much pressure can be produced with a 3 in. diameter (d) cylinder and 50 lb of force? Formula A r Sub / Solve A (1.5 ) Final A 7.1in. Formula Sub / Solve Final d = 3 in. p =? F = 50 lb A =? p F A 50 lb p 7.1in. lb 7.0 in. p

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. p 1 (V 1 ) = p (V ) NASA 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? p 1 = 60. lb/in. V 1 = 40. in. 3 p =? V = 10. in. 3 Convert p 1 to absolute pressure. p 1 = 60. lb/in lb/in. = 74.7 lb/in. Formula p(v 1 ) 1 (V p) lb Sub / Solve 74.7 (40.in. ) (10.in. p ) in. 988 in. lb p 3 10.in. Final p lb in 3 3

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 V T V 1 T 1 Note: T 1 and T refer to absolute temperature.

18 Charles' Law Example An expandable container is filled with 8 in. 3 of air and is sitting in ice water that is 3 F. The container is removed from the icy water and is heated to 00. F. What is the resulting volume? V 1 = 8in. 3 V =? T 1 = 3 F T = 00. F Convert T to absolute temperature. T 1 = 3 F F = 49 R T = 00. F F = 660 R

19 Charles' Law Example An expandable container is filled with 8 in. 3 of air and is sitting in ice water that is 3 F. The container is removed from the icy water and is heated to 00 F. What is the resulting volume? V 1 = 8in. 3 V =? T 1 = 3 F T = 00. F Convert T to absolute temperature T 1 = 3 F F = 49 R T = 00 F F = 660 R Formula V T V T in. V Sub / Solve 49 R 660. R in R 49 R Final V 38 in. V 3

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. p p 1 T T 1 Note: T 1 and T refer to absolute temperature. p 1 and p 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 6 F, and the pressure gauge reads 10. lb/in.. 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 T 1 = 6 F p 1 = 10 lb/in T = 90 F p =? Convert p to absolute pressure. p 1 = 10 lb/in lb/in. = lb/in Sub / Solve Formula p T p T lb / in. p 5 R 550. R lb / in R p 5 R Convert T to absolute temperature. T 1 = 6 F F = 5 R T = 90 F F = 550 R Final p 140 lb / in.

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 6 F, and the pressure gauge reads 10 lb/in. By afternoon the temperature inside the tank is expected to be closer to 90 F. What will the absolute pressure be at that point? Final p lb / in. If the absolute pressure is lb/in, what is the pressure reading at the gauge? lb/in 14.7 lb/in = 17. lb/in

23 Common Pneumatic System Components Transmission Lines Regulator Receiver Tank Drain Filter Directional Control Valve Pressure Relief Valve Compressor National Fluid Power Association & Fluid Power Distributors Association Cylinder

24 Compressor Types Compair Reciprocating Piston Compressor

25 Compressor Types Compair Rotary Screw Compressor

26 Compressor Types 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. (008). Compressed air explained: The three types of compressors. Retrieved March 5, 008, from Explained-- 03The_three_types_of_compressors.aspx Johnson, J.L. (00). Introduction to fluid power. United States: Thomson Learning, Inc. Microsoft, Inc. (008). Clip Art. Retrieved January 10, 008, from National Aeronautics and Space Administration. (008). Boyle s law. Retrieved February 3, 008, from National Fluid Power Association. (008). What is fluid power. Retrieved February 15, 008, 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 9, 008, from