How does it work? The blind cap unscrews and there is a Parker-looking button but it doesn't move. Inside the pen, with the section removed I can see a plunger looking device but how does it work? Is it frozen? I understand the principle of the vacuum fill Sheaffer pens, but this is not the same. The imprint on the barrel says Vacuum-Fil Ft. Madision Ia USA U.S. PAT. RE 19,167 OTHER PAT. PEND. The clip says Vacuum Fil

The nib says Vacuum Fil Writes Two Ways made in USA

It is similar to the Sheaffer-labelled plunger pens save that the blind cap is removable and one must pull back the stem rather than the blind cap. These usually need restoration, which can be a pain as some of the early (?) ones have stem different diameter from later Sheaffers.

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Thank you David. With that knowledge, I was able to get the parts moving again. It will need to get someone to put in new gaskets... someday.