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

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

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.

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

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

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.

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

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

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

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 120.0 psi, what is the absolute pressure? 120.0 lb/in.2 + 14.7 lb/in.2 = 134.7 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.

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 + 460. 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 + 460. = 525 °R

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.

Pascal’s Law Example How much pressure can be produced with a 3 in. diameter (d) cylinder and 50 lb of force? d = 3 in. p = ? F = 50 lb A = ?

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

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

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.2 + 14.7 lb/in.2 = 74.7 lb/in.2

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.

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 + 460.°F =492°R T2 = 200.°F + 460.°F =660°R The temperature readings must be converted to absolute temperature in order for the equation to work.

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 + 460.°F = 492°R T2 = 200°F + 460.°F = 660°R

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.

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.2 + 14.7 lb/in.2 = 134.7 lb/in.2 Convert T to absolute temperature. T1 = 62°F + 460.°F = 522°R T2 = 90.°F + 460.°F = 550.°R

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 141.9 lb/in.2, what is the pressure reading at the gauge? 141.9 lb/in.2 – 14.7 lb/in.2 = 127.2 lb/in.2 = 130 lb/in.2

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

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

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

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

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

Image Resources Compair. (2008). Compressed air explained: The three types of compressors. Retrieved March 5, 2008, from http://www.compair.com/About_Us/Compressed_Air 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 http://office.microsoft.com/en-us/clipart/default.aspx National Aeronautics and Space Administration. (2008). Boyle’s law. Retrieved February 3, 2008, from http://www.grc.nasa.gov/ National Fluid Power Association. (2008). What is fluid power. Retrieved February 15, 2008, from http://www.nfpa.com/OurIndustry/OurInd_AboutFP 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 http://zapatopi.net/inteli-tube/