How Pneumatic Capsule Pipelines Work
Basic Pneumatic, Steam or Hydraulic Cylinder
Figure 1 shows a simple cylinder that may be powered by steam, air or fluid. It consists of a cylinder, piston and rod. When a differential of pressure is applied across the piston, the piston moves towards the lower pressure. This differential can be created by pressure against atmosphere; atmosphere against vacuum; pressure against vacuum. Only Pneumatic systems are discussed herein.
Pneumatic Tube System
Figure 2 is the same as Figure 1 except that the piston rod has been removed and replaced by a container. In reality the container becomes the piston as in a Pneumatic Tube System.
Pneumatic Capsule Pipeline
Figure 3 has the piston and container supported by wheels to carry a heavy load and reduce the drag friction as in a people-carrying subway or a Pneumatic Capsule Pipeline.
There are two basic types of systems
Twin Line System
Two pipes are required. One to move a capsule or train from A to B and a second to move the capsule or train by a uni-directional airflow from B to A.
For the simplification of ALL drawings, the terminal equipment, blowers and valves, etc., are not shown.
Single Line Reversing System
A single pipe is used to convey a capsule or train from C to D and back by an airflow that is reversible.
Both of these types of systems can have switching devices, boosters, air filters, etc.
Suggest you read the attached papers in order to understand more of the technical aspects of the subject.
The Single Line system is usually one or two sizes larger in diameter than a Twin Line System in order to carry the same quantity of material in a given time.
Economically the Single Line Reversing Systems are about 60 to 70 percent of the capital cost of a Twin Line System. The operating cost of a Single Line Reversing System is 50 to 60 percent of a Twin Line System.