Forging new generations of engineers. Pneumatics.
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Transcript of Forging new generations of engineers. Pneumatics.
Forging new generations of engineers
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
BellowsTool 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
Early Pneumatic UsesAmerica’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 PressureGauge 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
Properties of Gases
Absolute PressurePressure (P) is measured in pounds per
square inch- lb/in.2 or psi
Standard atmospheric pressure - 14.7 lb/in.2
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 Temperature0°F and 0°C don’t represent TRUE ZERO°Absolute Zero = -460°F or -273°CAbsolute Temperature is measured in
degrees Rankine (°R = °F + 460 °) <- English/Std.
degrees Kelvin (°K= °C + 273 °) <- Metric
Example: If the air temperature in a system is 65 °F what is the absolute temperature?
65 °F + 460. = 525 °R
Properties of GasesBoyle’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 GasesBoyle’s Law continued
Properties of GasesCharles’s Law
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
When the pressure of a confined gas remains constant, the volume of the gas is directly proportional to the absolute temperature.
Properties of GasesCharles’s Law continued
V1 = V2
T1 T2
Where:V1 = initial volumeV2 = resulting volumeT1 = initial absolute temperatureT2 = 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.
V2 = V1 x T2
T1
V2 = V1 x 672
492= 1.36 V1
FahrenheitAbsolute is 460 +Fahrenheit
Isobaric - equal pressure
Properties of GasesGay-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
__ __
Properties of GasesIdeal Gas Law
Combining the work of Charles, Gay-Lussac, and Boyle we obtain:
P1V1 = P2V2
T1 T2
___ ___
Which was the main precursor to the modern day ideal gas Law:
PV=nRT
Properties of GasesPascal’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
FA
p
Symbol Definition Example Unit
p Pressure lb/in.2
F Force lb
A Area in.2
Properties of GasesPascal’s Law
Pascal’s Law Example
How much pressure can be produced with a 3 in. diameter (d) cylinder and 50 lb of force?
p 2
lbFinal 7.0
in.
2Final A 7.1in.
2Sub/Solve A ( 1.5 )
2Formula A r
p 2
50lbSub/Solve
7.1in.
pF
FormulaA
d = 3 in. p = ?F = 50 lb A = ?
Common Pneumatic System Components
National Fluid Power Association & Fluid Power Distributors Association
Receiver Tank
Compressor
Transmission Lines
Cylinder
Pressure Relief Valve
Directional Control
Valve
Filter
Regulator
Drain
Future Pneumatic Possibilities
What possibilities may be on the horizon for pneumatic power?
Could it be human transport?
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