This is basically a syringe filler combined with the Dunn pump system. The seal is around the reciprocating rod head. The rod is open in the middle so it can also fill (so is the Dunn). Like the Dunn filler, air is displaced by the pump rod, and ink is pulled in on the upstroke. The differences between this and the Dunn filler are that 1) the seal is on the plunger head, while on the Dunn it is the end of the barrel sealed to the rod, and 2) since it is a converter, the Noodler is left pulled back and full of ink while the Dunn is returned to the down stroke position when done. The Dunn pen can fill the plunger rod and barrel for extra capacity, but you would have to leave the plunger pulled back! Perhaps the difference is too minor to be its own filler, but the intent is clearly different based on the location of the seal and the intent to fill the plunger handle and leave it pulled back more like a syringe filler.