My mother just sent me five old pens. Three Parker 51's in various functioning. One piston fill still works, the others do not.
This is a Sheaffer with a nice 14K nib and a barrel piston fill.
Can anyone tell me about this pen?

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Thanks.

Your pen appears to be a Touchdown filler. It can be a a very nice pen with a bit of restoration. A great reference for the filling system is on Richard's site under the reference info tab. Look for Design Features: Pneumatic Pens and there is information on the touchdown filler.

The basic principle to remember is that the pen fills on the down stroke of the touchdown tube. You pull the tube out, immerse the nib in ink, depress the touchdown tube and hold the pen in the ink for ten seconds or so. This will fill the pen if everything is in good shape.

The pen is an easy restoration. You need a new "O" ring, a new sac, and some time to research the restoration. Do some searching around FPN for Touchdown and you'll likely find what you need. If not, ask back here or on the Repair Q&A forum.

This is indeed the touchdown filler.These pens are easy to get restored (for those who know how to do it).
The pen doesnt have a lot of value but with some TLC can be a wonderful reliable writer.

I've got one of these on the way back from having the sac and ring replaced.