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Big and Flabby

Posted by Dirck on 6 June, 2013

The current desk pen, a Wahl Oxford with a pleasant semi-flex point, is not an efficient creature.  I find that I have to fill it on a three day schedule, unlike the various Sheaffers and Parkers I’ve used previously which have gone for a week or two.  This has turned my thoughts to the idea of capacity, and since I’m a fussy pedant about some things, I can turn up actual objective data:

Pen Capacity in ml
  • Wahl
  • Sheaffer fat TD
  • Sheaffer Snorkel
  • Parker 51 vac
  • Parker 51 aero
  • 1.3
  • 1.1
  • 0.8
  • 1.5
  • 1.5

No wonder, then, that I’ve had a “51” run for more than two weeks between fill-ups.  I put the Wahl’s relatively poor mileage down to plenty of evaporation around a pathetically simple feed (seven shallow cuts a side!), but as my thoughts are more on tank size than consumption, I need to point out a thing related to size.  Let me lay a couple of these pens side-by-side:

Sheaffer Snorkel

Wahl Oxford

“51” Vacumatic

Alas, no x-ray view, but the slight difference in size of frame is there to allow me to admit the Wahl at the same scale as the other two– it’s a long pen.  It’s also got the least non-storage space inside it, with a very simple lever filler.  The Snorkel’s sac doesn’t reach back much beyond the CO. in the impression, and is wrapped in three layers of steel so of course it doesn’t hold much.  The “51” has about a third of the space between the clutch ring and the barely-visible tail seam filled with filler, so its ink-bearing space is rather limited relative to its exterior dimensions.  The sac in the Wahl reaches very nearly all the way back to the end of the marbled body, and is not much under the diameter of the barrel.  So… why so little ink?

The answer, I believe, is because it’s a very large sac.  The filler relies on the power of the rubber to retain its shape; it draws ink while returned to that shape after being flattened.  Extremely large sacs have a vast internal capacity, but it seems to me that once a certain weight of ink comes aboard, the rubber can’t support any more, and just wobbles around trying to hold onto what it’s managed to take.  A big pen doesn’t necessarily hold a vast ocean of ink.

One more example, with another couple of pens side-by-each for close examination:

Sheaffer 8C (quite old)

Sheaffer No Nonsense (rather less old)

Similar in size and shape, yes?  The old fellow is a little bigger, certainly, and like the Wahl relies on a lever and a sac for filling.  The sac takes up the majority of the interior space of the pen, and pulls in 1.4 ml of ink.  The No Nonsense, if treated as an eyedropper and devoting all interior space to ink, can carry a sloshing 3.6 ml.  I’m reasonably sure, without committing an act of scientific investigation, that the mechanism of the lever and other dead space inside in the oldster doesn’t account for 2 ml of volume.

I don’t really have a point, which is usually the case with these little rambles, apart from sharing the enjoyment of a little paradox; a bigger pen does not necessarily carry the most ink.  As least, not so long as there’s a sac involved.  It’s just fun to know stuff.

Today’s pen: Waterman Carène (which is reasonably large, as pens go)
Today’s ink: Herbin Bleu Myosotis (although the teeny little 0.6ml cartridge is nearly exhausted)

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6 Responses to “Big and Flabby”

  1. Dale said

    I have a snorkel desk pen just like yours. Beautifully smooth writer, and never fails to start!

    • They are a treat, and mine is on standby for when I tire of the constant feeding the Oxford is demanding. I sort of want to like the fat TD more, but the Snorkel has given me less guff in general.

  2. I’ve never used a desk pen, actually. 51s hold an astonishing amount of ink. I filled one and I was stunned at how long I could go before a refill. The Pelikans are pretty good for ink capacity as well.

    • One of the few blessings of Regular Job is a desk I can call my own and station a desk pen upon; people in a similar situation really should try it because the convenience is delightful.

      Some time ago I was doing an endurance test on the 51 and was on the edge of believing pixies were refilling the thing. Pelikans do have good bunkerage, although the damp nature of the points tends to run through it pretty fast. TWSBI, the imps, seem to have got the mechanism/storage laurel in piston fillers, though.

  3. Claire said

    Thanks for the thoughtful post. My mental meanderings lead me to wonder what impact the pressure bar has in the equation. I have no idea how variable in size they are, in relation to the sac size, but the amount of air expelled (and consequently, ink sucked in) will vary in direct relationship to the size of the bar, not the sac- I would think. So an oversized sac will not draw in more ink if it’s pressure bar cannot expel all the air. What do you think?
    And snorkels – well they are snorkels and we love them despite their puny capacity.
    (sorry, I know I’m late getting to this post.)

    • I don’t think the bar has a huge role to play, as they’re a fairly consistent proportion of the sac’s width so they fit easily in the barrel– a particularly skinny one in a relatively wide pen would probably be a handicap, but they generally don’t appear. There are cheaper bars, too, which press mainly at one end of the sac (the same arrangement as a “51” aero set-up, but that gets away with it through filling over several squeezes) and they certainly lead to an inefficient use of the sac.

      One other thing occurs to me in this– the sac tends to fold under the pressure rather than collapse only under the bar; a cross-section would look like a smile rather than a bent bar-bell. The difference between bar and sac width would have to be pretty substantial before it would come into play.

      Ah, snorkels– love, respect and covet, indeed. If I weren’t going on vacation next week, I’d have followed through on my plan to supplant the Wahl with one already.

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