Compressed air; here is a broad range of general information about compressed air.
There are three commonly used energy sources for industry.
Compressed air is an energy source that's relatively easy to store, is non-flammable, is very powerful, can generate high speed in a variety of ways including air actuators, and is extremely versatile in the variety of ways it is used.
For example, it can provide an air cushion upon which we drive our vehicles. The air inside the tire is "pumped" into the it with a manual bicycle type air compressor, or via the compressed air hose from the air compressor that's located somewhere inside the local tire store or corner garage.
It still is if you chose to use that hand compressor, the bicycle tire pump. But who wants to do that?
With compressed air you can rough or fine finish the surface of a piece of woodwork or smooth weldments in steel with an air sander or grinder.
Compressed air is used everywhere.
Compressed air helps people breathe underwater with portable SCUBA tanks, in an environment that is foreign and deadly to them.
If you're one of those folks with an interest in SCUBA, sorry about that! Much as there is huge appeal for using Self Contained Underwater Breathing Apparatus this site has to do with industrial and home uses of compressed air.
And as mentioned earlier, compressed air is relatively safe in that it's non-flammable. When you spill compressed air, it doesn't make a mess!
This stored energy, in the form of compressed air, is now at imbalance, in that you have an area of high pressure in a compressor tank surrounded by an area of lower pressure; the atmosphere.
That drive to achieve balance in nature - that is, to get the compressed air from an area of high pressure back to atmospheric pressure, means that when you open the valve on the tank or air line, air will move at almost the speed of sound, rushing from high to low pressure, to get back to 14.7 PSI, which is one atmosphere at sea level.
By controlling this flow of air, and directing it into tools that in themselves can perform work, then you can extract the work energy from the compressed air energy as it decompresses back to atmospheric levels.
Over the years, mankind has learned how to use this high-to-low pressure flow of air to do work for us via specialty nozzles, air tools, air actuators, air motors, and so on. Compressed air really is a neat way to store and use energy.
Therefore, fire or explosion risk can be reduced to an acceptable level when using compressed air equipment in almost all flammable operations. Compressed air can be used in applications where other energy forms might blow you to kingdom come!
Using hydraulic energy is more expensive in generation of energy to do work, and in the cost of the components to use hydraulic force. If you don't need the immense pressures and force that hydraulics can give you, it doesn't make sense to pay for that capability.