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Forging new generations of engineersPowerPoint Presentation

Forging new generations of engineers

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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)

Pneumaticsvs.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.

Showed that a vacuum can be created

Created hemispheres held together by atmospheric pressure

EarlyPneumaticUsesDesigned by Alfred Beach

Built in New York City

Completed in 1870

312 feet long, 8 feet in diameter

Closed in 1873

EarlyPneumaticUsesProperties 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 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 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 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 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

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 GasesCharles’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 +

Fahrenheit

V2 = V1x 672

492

V2 = V1 x T2

T1

=

1.36 V1

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

__ __

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:

PV=nRT

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

Pascal’s Law ExampleHow 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 = ?

Regulator

Filter

Directional Control Valve

Drain

ReceiverTank

Cylinder

Pressure Relief Valve

Compressor

Common Pneumatic System ComponentsNational 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

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