How is such high pressure achieved?

The function of Radulock is remarkably simple. When a tube is pressurised, it expands. This so-called, "hoop-stress" (after the stress borne by the iron hoops around a wine barrel) is borne by the walls of the tube, causing it to stretch. Ordinarily, for a tube that is forced over the top of a barb-type fitting, the pressure in the tube reaches a point where the hoop stress matches the elastic stress holding the tube onto the barb (roughly) and the connection bursts. Radulock geometry has simply turned the problem around. The tube is compressed, rather than stretched into a small retaining gland so that the outside of the tube presses into the constriction, forming a seal. Since the hoop stress derived from fluid pressure and the elastic force of the tube acts in the same direction (producing a net force outwards), the pressure between the tube and the port structure always exceeds the internal pressure - so it won't leak.

There are some other considerations, but generally this simple relation provides that allows Radulock ports to hold such high pressure. Radulock ports have been tested to well in excess of 100 bar (or 10 MPa) for 0.060" OD (~1.5 mm) microbore Tygon and EVA tubing (in fact up to around 180 bar at which point some other part of the test rig failed. This is well above the working pressure of the tubes themselves), common in both medical and laboratory applications. Measurements were inaccurate above 1.1 MPa hence the lower cited value.