Forging new generations of engineers Fluid Power Principles of EngineeringTM Unit 4 - Lesson 4.3 – Fluid Systems Forging new generations of engineers Project Lead The Way, Inc. Copyright 2007

Pneumatics

Properties of Compressed Air Components have long working life resulting in longer system reliability Environmentally friendly Safety issues are minimized (but not eliminated) e.g.. Fire hazards; unaffected by overloads (hydraulic actuators stall or slip when overloaded) Pneumatic actuators in a system do not produce heat (except for friction)

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

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.

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 important variables 1. Temperature, T 2. Pressure, P 3. Volume, V Gas laws describe relationships between these variables

Pneumatic Power Pneumatics vs. hydraulics Pneumatic power 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

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 - 14.7 lb/in.2 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. Example: 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

Properties of Gases Absolute Temperature 0°F and 0°C don’t represent TRUE ZERO° Absolute Zero = -460°F or -273°C Absolute Temperature is measured in degrees Rankine (°R = °F + 460 °) <- English/Std. degrees Kelvin (°K= °C + 273 °) <- Metric 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. Example: If the air temperature in a system is 65 °F what is the absolute temperature? 65 °F + 460. = 525 °R

Properties of Gases Boyle’s Law The pressure of a given mass of gas is inversely proportional to its volume (providing the gas remains at constant temperature) Isothermic (equal temperature)

Properties of Gases Boyle’s Law continued

Properties of Gases Charles’s Law When the pressure of a confined gas remains constant, the volume of the gas is directly proportional to the absolute temperature. A given mass of gas increases in volume by: 1/273 of its volume per degree Celsius rise 1/459.7 of its volume per degree Fahrenheit rise

Properties of Gases Charles’s Law continued Isobaric - equal pressure V1 = V2 T1 T2 Where: V1 = initial volume V2 = resulting volume T1 = initial absolute temperature T2 = resulting absolute temperature A volume of air in an accumulator is submerged in a bucket of ice water (32 degrees F). If you remove the accumulator from the ice water and place it in a bucket of boiling water what would the resulting volume be. Fahrenheit Absolute is 460 + V2 = V1 x 672 492 V2 = V1 x T2 T1 = 1.36 V1

__ __ Properties of Gases P1 = P2 T1 T2 Gay-Lussac's Law When the volume of a confined gas remains constant, the pressure of the gas is inversely proportional to the absolute temperature. P1 = P2 T1 T2 __ __

PV=nRT ___ ___ Properties of Gases P1V1 = P2V2 T1 T2 Ideal Gas Law ___ ___ Combining the work of Charles, Gay-Lussac, and Boyle we obtain: Which was the main precursor to the modern day ideal gas Law: PV=nRT

Properties of Gases 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

Pascal’s Law Example Properties of Gases Pascal’s Law 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 = ?

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

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