How can a carrier travel through a pneumatic tube?

A small container slips into a station, disappears into a tube and arrives elsewhere in the building. No tiny engine rides inside it. In a pneumatic tube system, air pressure supplies the driving force, while the tube guides the journey. Such systems have carried mail and now move suitable small items between places such as hospital departments.

The traveling container is called a carrier. It fits closely inside the tube, often with bands around its ends. A blower changes the air pressure on its two sides. Air presses on both ends, but when pressure behind is higher than pressure ahead, the backward side pushes harder. The difference gives the carrier a forward force.

That difference can be created in two ways. The system can increase pressure behind the carrier or remove some air ahead of it. Lower pressure ahead is often called suction, but empty space does not reach out and grab the carrier. Air remaining behind still provides the stronger push. Changing which side has higher pressure changes the direction of the driving force.

The close fit matters because too much air escaping around the carrier would make the pressure difference harder to maintain. Friction against the tube resists motion, and bends change the route. The blower supplies energy to keep air moving; the carrier cannot travel indefinitely just because it is enclosed in a tube.

In a larger network, switching sections called diverters connect a route to the selected destination. Controls coordinate the trip and slow the carrier as it arrives. The result is a transport network inside a building: containers carry the objects, tubes choose the possible paths, and an invisible difference in air pressure does the pushing.