Antique cigarette lighter

I have inherited this lighter from an uncle. I do not know how it works or what fuel it takes. It does not have a flint wheel. The "arm" is spring loaded and must de depressed to open the jet section. The arm then goes to the position in the 2nd photo. Is it a pressure pump? The filler(?) hole, bottom screw, contains a tube that goes to a jet. I can see through it. The plunger arm has a knurled edge at the top of the body but I can't undo it.
I hope someone can give me some information on it. Cheers, greg