Appearing only in the Safari, this version of the pneumatic filler system is slightly different from that which Sheaffer was using at the same time. It actually shares some of the aspects of vacuum-filler system, relying on a shaft-mounted valve to generate the necessary pressures. However, the system is rather simpler and more robust than either of the methods used by Sheaffer, and as a result, Safaris are usually found to not need the maintenance which their construction renders impossible.
The core of the system is a loose ring trapped between two discs at the inner end of the piston shaft. This ring contacts the outer edge of the barrel, but is entirely free of the shaft itself. In the upstroke, it is drawn against the lower disc, which has slots cut in it. Air can pass freely around the shaft where it passes into the barrel, past the outside edge of the upper disc and then through the inside of the ring and through the lower disc’s slots. Thus, on the upstroke, there is no change of interior pressure whatever; this avoids both the need for Sheaffer’s sac protector’s anti-distention role and the danger of drawing ink up inside the pen .
On the downstroke, the free ring is pressed against the solid upper ring, sealing the interior of the barrel. This runs the pressure up, collapsing the sac. At the bottom of the stroke, the interior of the barrel widens in much the same way as a vacuum-filler’s, and here the seal is broken, allowing the sac to re-inflate and take in ink. The moving piston and the sac never touch one another, and the other role of the sac protector as a pinching preventative is also abolished.