why the progressive change in pipe diameter in pneumatic transport?
When handling any fluid , if you add or rest flow make to change the diameter in a direct proportion.
There are diefferents way of sizing a duct .
One is to keep the speed all the duct the same.
Other is to size it as to have all the lenght the same uniatry pressure drop.
Sure your system have branchs that add or rest flows, thats the razon
as in your route system , roads, street, route, highway, expressway
more cars , wide the way.