The tube extruding process starts with the un-vulcanized rubber compound being fed into an extruder. Then, low air pressure is injected into the die which flows through the center of the pin that makes up the inner part of the extrusion die, and then directly into the semi-fluid tubing as it is coming out of the die.
True pressure regulators are then required to set wall thickness. Proportion-Air can help regulate pressures very accurately in this process.
In this application, two QB3s are being used to extrude rubber tubing. One QB3 is controlling positive pressure (generally, this pressure is in the inches of water range) to control the I.D. (inner diameter) of the tube and the other QB3 is controlling vacuum around the tube to control tube thickness and O.D. (outer diameter). These two pressure control devices work together to set and maintain the wall thickness of the tube.
Learn more about the QB3.