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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