What should be the ink capacity of a Parker 51 Vacumatic Demi? I have a 1947 and do not feel like it holds as much as it could. It currently takes about 0.75ml of ink upon filling. The filler works fine and the original plastic breather tube is securely in place and not clogged.

I am a little suspicious, as I have to fill it daily when in rotation. It is a pretty wet writer, but the 20 or so other pens I have do not need filling nearly as often.

Also... with the hood off and everything else in place it expels air bubbles at the top of the collector (at the smaller groove) when I fill it with water. Is this normal?

Any suggestions would be greatly appreciated.

If I remember correctly, the 51s I've messed with expel air at the base of the collector, near the larger groove.

Cant help on the ml stuff. How much writing can you do with it?

I actually think I figured the problem out. If I wait 2-3 seconds between plunger depressions, the pen fills much more.

I'm not too sure on exactly how much writing I can do on one fill, but it is at least 3 a4 sized pages of notes.

A Vac-filling "51" in complete working order will hold a usable supply of about 1.2-1.3 ml of ink. For comparison, a standard short International cartridge holds 0.7 ml.

Just for fun, I replaced the breather tube with a slightly longer one and the pen now fills to 1.5 ml of ink.

Too long a tube, and the end of the tube will be immersed in the ink when the pen is clipped in your pocket. This will cause the pen to hork up ink when you go up in an airplane with the pen. In 1946 Parker patented a design with a tube that is short enough so that it's not in the ink when the pen is in the pocket. You get less ink in a fill, but this design prevents the leakage problem in airplanes.

That explains the large ink reservoir I saw when I removed the nib/collector assembly from my 51 vacumatic. I wondered at the disparity between it and the amount of ink taken into the pen.

I suspect also that if you have too long a tube, just the heating/expansion effect on the air in the reservoir from putting a cold pen into a warm shirt pocket could result in a dramatic leak...