BASIC CONCEPT
All contemporary PCP systems, such as those used in the former
Soviet Union for transporting rock (2) and those used in Japan
for transporting limestone and other products (3), use wheeled
capsules rolling through a pipeline. For capsule stability inside a
circular conduit (pipe), it is not permissible to mount wheels on
the bottom of capsules. Instead, two sets of wheels are mounted
on the two ends of each capsule as shown in Figure 1. Each
wheel set consists of a minimum of five small wheels placed in
symmetric position around the pipe interior in contact with the
pipe wall. The wheels are connected to the central axis of the
capsule and free to rotate around the pipe in a manner similar to
gimbals. In so doing, the capsule will always remain in a stable
equilibrium position without spilling the cargo. For PCPs that
use square or rectangular conduits, as used in Japan for tunnel construction
(4), the gimbals-type wheels are no longer needed. Such
PCPs use capsules with wheels mounted on capsule bottom, as in the
case of ordinary vehicles that run on flat horizontal surface. Most
current systems use rubber tires to minimize noise and prevent wear
of the pipeline.
The PCP capsules normally have a diameter approximately 85%
of the pipe diameter, and a capsule length about five times the capsule
diameter. This means the capsule length-to-diameter ratio, called the