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Forging new generations of engineers. Pneumatics. Properties of Compressed Air. Components have long working life resulting in longer system reliability Environmentally friendly

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properties of compressed air
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
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

Tool used by blacksmiths and smelters for working iron and other metals

early pneumatic uses1
Otto von Guericke

Showed that a vacuum can be created

Created hemispheres held together by atmospheric pressure

early pneumatic uses2
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
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
properties of gases1
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

properties of gases2
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

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 gases3
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

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
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 GasesCharles’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
Properties of GasesCharles’s Law continued

Isobaric - equal pressure

V1= V2

T1 T2


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.


Absolute is 460 +


V2 = V1x 672


V2 = V1 x T2



1.36 V1


Properties of Gases

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

__ __


Properties of Gases

Ideal Gas Law

P1V1= P2V2

T1 T2

___ ___

Combining the work of Charles, Gay-Lussac, and Boyle we obtain:

Which was the main precursor to the modern day ideal gas Law:



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

pascal s law example

Properties of Gases

Pascal’s Law

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 = ?

common pneumatic system components

Transmission Lines



Directional Control Valve




Pressure Relief Valve


Common Pneumatic System Components

National Fluid Power Association & Fluid Power Distributors Association

future pneumatic possibilities
Future Pneumatic Possibilities

What possibilities may be on the horizon for pneumatic power?

Could it be human transport?