Compressed air

Compressed air in vehicle tires and shock absorbers are commonly used for improved traction and reduced vibration.

Brakes applied by compressed air made large railway trains safer and more efficient to operate.

[4] In the 19th century, Paris had a system of pipes installed for municipal distribution of compressed air to power machines and to operate generators for lighting.

[7] Air under moderately high pressure, such as is used when diving below about 20 metres (70 ft), has an increasing narcotic effect on the nervous system.

For diving much beyond 30 metres (100 ft), it is less safe to use air alone and special breathing mixes containing helium are often used.

[8] In industry, compressed air is so widely used that it is often regarded as the fourth utility, after electricity, natural gas and water.

However, compressed air is more expensive than the other three utilities when evaluated on a per unit energy delivered basis.

Drain valves may be installed at multiple points of a large system to allow trapped water to be blown out.