Pneumatics

Preserved Porter Locomotive Company No. 3290 of 1923.

Pneumatics is a section of technology that deals with the study and application of pressurized gas to effect mechanical motion.

Pneumatic systems are extensively used in industry, where factories are commonly plumbed with compressed air or compressed inert gases. This is because a centrally located and electrically powered compressor that powers cylinders and other pneumatic devices through solenoid valves is often able to provide motive power in a cheaper, safer, more flexible, and more reliable way than a large number of electric motors and actuators.

Pneumatics also has applications in dentistry, construction, mining, and other areas.

Examples of pneumatic systems and components

Air brakes on buses and trucks
Air brakes, on trains
Air compressors
Air engines for pneumatically powered vehicles
Barostat systems used in Neurogastroenterology and for researching electricity
Cable jetting, a way to install cables in ducts
Compressed-air engine and compressed-air vehicles
Gas-operated reloading
Holman Projector, a pneumatic anti-aircraft weapon
Inflatable structures
Lego pneumatics can be used to build pneumatic models
Exercise machines

Pipe organs:
- Electro-pneumatic action
- Tubular-pneumatic action

Pneumatic tools:
- Jackhammer used by road workers
- Pneumatic nailgun

Vacuum pump

Gases used in pneumatic systems

Pneumatic systems in fixed installations such as factories use compressed air because a sustainable supply can be made by compressing atmospheric air. The air usually has moisture removed and a small quantity of oil added at the compressor, to avoid corrosion of mechanical components and to lubricate them.

Factory-plumbed, pneumatic-power users need not worry about poisonous leakages as the gas is commonly just air. Smaller or stand-alone systems can use other compressed gases which are an asphyxiation hazard, such as nitrogen - often referred to as OFN (oxygen-free nitrogen), when supplied in cylinders.

Any compressed gas other than air is an asphyxiation hazard - including nitrogen, which makes up 77% of air. Compressed oxygen (approx. 23% of air) would not asphyxiate, but it would be an extreme fire hazard, so is never used in pneumatically powered devices.

Portable pneumatic tools and small vehicles such as Robot Wars machines and other hobbyist applications are often powered by compressed carbon dioxide because containers designed to hold it such as soda stream canisters and fire extinguishers are readily available, and the phase change between liquid and gas makes it possible to obtain a larger volume of compressed gas from a lighter container than compressed air would allow. Carbon dioxide is an asphyxiant and can also be a freezing hazard when vented inappropriately.

Comparison to hydraulics

Both pneumatics and hydraulics are applications of fluid power. Pneumatics uses an easily compressible gas such as air or a suitable pure gas, while hydraulics uses relatively incompressible liquid media such as oil. Most industrial pneumatic applications use pressures of about 80 to 100 pounds per square inch (550 to 690 kPa). Hydraulics applications commonly use from 1,000 to 5,000 psi (6.9 to 34.5 MPa), but specialized applications may exceed 10,000 psi (69 MPa).

Advantages of pneumatics

Simplicity of Design And Control
- Machines are easily designed using standard cylinders & other components. Machines operate by simple ON - OFF type control.
Reliability
- Pneumatic systems tend to have long operating lives and require very little maintenance.
- Because gas is compressible, the equipment is less likely to be damaged by shock. The gas in pneumatics absorbs excessive force, whereas the fluid of hydraulics directly transfers force.
Storage
- Compressed gas can be stored, allowing the use of machines when electrical power is lost.
Safety
- Very low chance of fire (compared to hydraulic oil).
- Machines can be designed to be overload safe.

Advantages of hydraulics

Liquid (as a gas is also a 'fluid') does not absorb any of the supplied energy.
Capable of moving much higher loads and providing much higher forces due to the incompressibility.
The hydraulic working fluid is basically incompressible, leading to a minimum of spring action. When hydraulic fluid flow is stopped, the slightest motion of the load releases the pressure on the load; there is no need to "bleed off" pressurized air to release the pressure on the load.

Pneumatic logic

Pneumatic logic systems (sometimes called air logic control) are often used to control industrial processes, consisting of primary logic units such as:

And Units
Or Units
'Relay or Booster' Units
Latching Units
'Timer' Units
Sorteberg relay
Fluidics amplifiers with no moving parts other than the air itself

Pneumatic logic is a reliable and functional control method for industrial processes. In recent years, these systems have largely been replaced by electrical control systems, due to the smaller size and lower cost of electrical components. Pneumatic devices are still used in processes where compressed air is the only energy source available or upgrade cost, safety, and other considerations outweigh the advantage of modern digital control.

References

Compressed Air Operations Manual, ISBN 0-07-147526-5, McGraw Hill Book Company

External links