Pneumatic air sources
This page lists some of the common sources of air pressure to power a pneumatic, and the advantages and disadvantages of each:
Gases
Acetylene
Advantages:
- Very powerful combustion pressure spikes
Disadvantages:
- Extremely unstable, will auto-ignite at pressues over 15 psi
- Pressure spikes are very rapid, and therefore can cause fatigue much more readily
Air
Advantages:
- It's price (completely free of course)
- Global availability.
- Inert
Disadvantages:
- Limited performance approaching the sound barrier.
Performance of air is moderate. It is very uncommon for a air powered launcher to exceed the sound barrier, but not completely impossible. Most gases are compared against air as a benchmark Sources: If you want to use air, you'll either need a compressor, hand/foot pump or a High Pressure Air (HPA) tank
Helium
Advantages:
- Exceptional performance
- High speed of sound and particle speed
- Inert
Disadvantages:
- Costly
- Will leak faster than any other gas
- Helium regulators typically limited to 200 psi.
Performance is second only to Hydrogen. Sources: Unless you have an on-site extraction plant, the only option is gas bottles
Nitrogen
Advantages:
- Performance slightly better than air.
- Option for high pressures.
- Inert
Disadvantages:
- Costly
- Particle speed is not significantly more than that of air
Nitrogen is slightly more powerful than air for a given pressure, but nitrogen regulators are capable of very high pressures. Sources: Unless you have an on-site extraction plant, the only option is gas bottles
Hydrogen
Advantages:
- Highest performance gas, in terms of perticle speed
Disadvantages:
- Costly.
- Potential explosive risk.
- Will leak fast.
Hydrogen is the most powerful gas that can be used in a pneumatic, but it has numerous risks associated with it. Sources: Unless you have an on-site extraction plant, the only option is gas bottles or electrolysis
Carbon Dioxide
Advantages:
- Reasonably cheap
- High pressure
- Highest gas volume to bottle volume ratio
- Inert
Disadvantages:
- Low power due to high molar mass and high density
- Very heavy cooling on decompression (can cause problems with PVC launchers)
CO2 is a very common bottled gas, but it's power is limited by it's high density. Sources: Gas bottles, Gas bulbs
Propane
Advantages:
- Reasonably cheap
- High gas volume to bottle volume ratio
- Readily available
Disadvantages:
- Low power
- Low pressure
- Possible (if unlikely) fire risk
Propane is better known as a combustion cannon power source, but some pneumatics have used it as a gas. It's performance is low, because of it's high density and low pressures, but it is cheap and easily found. Sources: Gas bottles, either in large bulk tanks of several kilograms, or in small tanks of 0.5 - 1 lb.
