Normal pipelines can not transport solid goods; they can not transport people. Some solid goods can be mixed with a liquid or a gas and transported along a pipeline. This is normally called slurrying. Solid goods like grain or china clay can be slurried. Most solid goods can not be transported in this way.
The alternative is to put goods (or people) into a sealed container, a capsule. The capsule is then transported along the pipeline. When the capsule reaches the destination, the goods are removed from the capsule.
Capsule pipelines are used like a railway. You get into the railway carriage at a station. The carriage moves along the railway track till it reaches the next station, where you get out.
How is the capsule actually made to move along the pipeline? One of three different technologies are used.
The most common technology is the use of air, called pneumatics. The capsule has the same diameter (width) as the pipeline, so not much air can get past it. Air is pumped into the pipeline behind the capsule. Sometimes air is pumped out of the pipeline in front of the capsule. The force of the air behind the capsule is greater than the force of air in front of the capsule. The capsule moves forward.
Water can be used to push capsules along, instead of air.
The newest technology uses complicated sets electric cable, which act like sets of magnets. These magnets constantly pull the capsule forward along the pipe. These work like 'mag-lev' trains.
Think about it...
