Screw Them Vac Fillers!

If you’ve ever written with or read about a problem with vac-filling pens (such as the Pilot Custom 823 or TWSBI Vac-700) drying up after writing for a few minutes, you will definitely want to check out this video. The solution to your problem could be so simple you’ll slap your forehead. Long-story short, you need to unscrew the back filler knob when you write in order to ensure proper ink flow.


Because there’s an o-ring on the end of the filler rod that seals up the ink chamber, and unless you unscrew the back of the pen, you are essentially cutting off ink supply to your nib. You can still write for a bit (nearly 10 minutes in this video) before it dries up, but it’ll happen, eventually. Unscrewing that filler knob opens up the ink chamber and allows ink to go through the pen.

So why do pen companies design them this way? Any pen that holds this much ink (2ml or more in most vacuum fillers) can be prone to leaking due to pressure changes caused by elevation and temperature variations.  They seal them up so that leaking isn’t as likely to happen. It just means you have to unscrew the back knob. I’m not sure most fountain pen users are aware that vacuum filling pens require this, as I get a lot of questions from frustrated vac owners and read about it a lot on FPN.

Hopefully, this helps to clear up some of the confusion and mystique about vacuum-filling pens. I do love the design and think they’re a very novel way to fill a pen, and with this simple trick, it’s easy to enjoy your vac-filler as it was intended.

Here’s the letter I wrote while waiting for the pen to dry up after a fresh fill. It was pretty much a stream of consciousness, but ended up being kind of funny. Excuse the many spelling errors, I wasn’t going to accuracy, but more for speed!

Write On,
Brian Goulet

2017-10-11T03:38:46+00:00 March 14th, 2013|Tips & Tricks|39 Comments
  • Julie Louis

    I am surprised that it took you so long to get the nib to dry up. I never tried that, but realized every time I wrote with my 823 without unscrewing the knob that the Yama Budo ink I was using looked too light, more of a pink than I would want, which would remind me to unscrew the knob. I think that the people bewildered about 823s need to look at the cap. Mine had a sticker telling you to unscrew the nob before writing with it. Maybe their stickers got lost.

  • David Ragasdale

    When I get home, I take my cap off and sigh a sigh of relief. It just needs to breath!

  • David Ragasdale

    If the pen were completely full, there would have been less air to expand and it would have quit much sooner.

  • Adam

    I learned this in the instructions that came with the pen.

  • Adam


  • Adam

    I tried to post a picture of my directions but I can't.

  • Maria Camarão

    It just looks like bad engineering. Sort of like the infamous "antena gate" with the iPhone. If you buy a pen for that price it should write, point. I mean, a rollerball will write period, no fuss. I feel it defeats the purpose of spending money on a good pen, tho have to hack it every 10 minutes in order to write.

  • Karen Dockal

    You don't "hack it every 10 minutes." You open it to write, then close it when you're done. Very much like taking off the cap and putting it back on. It's an added safety measure to prevent leaks. Don't know how that is bad engineering.

  • Good to know, thanks!

  • nobody

    "Captain, I canna change the laws of physics!"

  • Or people don't read the stickers 😛 I purposely used a 'wet' ink, on a fresh fill, so that I could see just how long I would go. 10 minutes of writing was WAY more than I expected. If someone was just using their vac pen normally, then it could take a week or more to write with it that much…and if it started drying up then, I'm not sure most people would have thought about the knob unless they were conscious of it. I think a lot of it depends on how you write, too.

  • Haha, indeed!

  • I don't think that would matter, because with the filler knob tightened, the ink chamber is cut off from the feed anyway. That was the whole point of the exercise, to prove that it would dry up completely with the knob tightened, and then immediately flow again with it unscrewed.

  • C'mon, who reads instructions? 😉 You'd be surprised how many people still ask me about this, even with instructions.

  • Oh, I'm sorry about that. I don't know why you can't, you should be able to upload pics….

  • Exactly, I think the pen manufacturers would argue that it's good engineering, otherwise they wouldn't do it! What's really good engineering is that you can actually remove the o-ring that seals it up so that you don't have to unscrew the knob, but that's coming in a separate video 😉

  • You're very welcome 🙂

  • Andrew

    I don't know about the Pilot, , but if you take the Vac700 apart, you can remove a small seal, and it will allow for continuous flow to the nib, however, you do lose the shut-off capability of the pen.

  • David

    How come you don't have to do this with a vintage Parker Vacumatic?

  • Adam

    I'm a rookie FP user and terrified of breaking stuff. If I hadn't read the directions I wouldn't have figured out how to fill the freakin thing!

  • Adam

    If you're talking for a custom 823 then I'm looking forward to those video!

  • Julie Louis

    The reason you don't unscrew a knob on the vintage Parker Vacumatic is that it is different kind of filling mechanism, that doesn't use a plunger. The Custom 823 is actually like a vintage Sheaffer Vacuum Fill pen, which does have a plunger you pull out and push in to fill it. Pilot (and possibly TWSBI, I really don't know much about their vac-fill pen) added the extra bit to shut off ink flow when the knob is screwed shut.

  • Waski_the_Squirrel

    When I first got my Pilot Custom 823, I was surprised when it ran out of ink: I knew to unscrew the knob, but it wasn't a habit yet. I was able to fill a few notebook pages of ordinary writing before it ran out. (I didn't scientifically measure it.) I haven't tried to measure writing with a TWSBI 700 either, but these two pens have caused me to dribble some ink with a TWSBI 540: I'm now in the habit of unscrewing the filling knob, and it doesn't work the same with this model!

  • Wow! This is amazing! I have a vintage Sheaffer Balance that has always had inconsistent ink flow. With the knob loosened a bit, it works great. Thanks!

  • Dusty

    What notebook are you using? I didn't see feathering, is there much bleedthrough/shadowing?

  • You can do this with both pens. I actually did a follow-up video showing this very process here:

  • See Julie's answer above 🙂

  • Thanks for your insight! I'm not very familiar with vintage pens. Both TWSBI and Pilot design their pens the same, like the Sheaffer.

  • I'm the same way, I've been using my 823 for about 6 months but never had it dry up on me until a few weeks back. I personally only use that pen for a half a page of writing at a time or less, and I change my colors a lot so I don't fill the pen up all the way. I was only writing with the ink that was in the feed, and never actually drawing from the body! Once I started getting more and more questions about it I did some testing, and finally, experienced the drying up for myself in 'real life'. If I hadn't known to look out for it, I could see how it would be frustrating! It's true that you do have to get in the habit of unscrewing the knob, it's not something you do with most pens.

  • Nice! I'm glad to hear that 🙂

  • Oh, well that's because I didn't zoom in very much. This is just a cheap Mead notebook from Target, and it spreads and bleeds pretty bad. This is a particularly well-behaved ink which is why it minimized the effects on the paper, but normally it's pretty unattractive. 😛

  • Dusty

    Aw, pity! I'm always on the search for more notebooks/paper. I want to try the Leuchtturms next, and really want to buy your Metropolitan package set but I'm still waiting patiently for the Metropolitans (black, zigzag pattern) to come back into stock!

  • Which pen? I've found with the TWSBI that you not only need to unscrew the back, but then pull on it a bit to break that o-ring seal. I've just pulled the o-ring off mine since I don't travel with it anyway. Now I don't have to worry about it 🙂

  • Brian

    Even with the valve unscrewed, I still have sudden episodes of running dry. I have to release valve 1-2mm and push it in to renew ink flow. What am I missing?

  • Ardis Charbonneau

    I didn't watch the video, I just read the post, and the notebook. I don't have a vac pen yet, but I keep looking at the TWSBI 700. What I'm really interested in is the ink. It's a beautiful shade. What is it? (Sorry if you mentioned it in the video.)

  • I used Pilot Iroshizuku Ama-Iro, sorry I didn't make note of that in the body of the post 🙂

  • With the Pilot just unscrewing the valve was enough to pop that seal, but on the TWSBI's I've found you actually need to pull up just a hair on the valve after unscrewing it to pop that seal. If it's still drying up after that, then it may be another issue altogether. I'd shoot TWSBI an email at and see if they can work with you on that, they're really good about it.

  • ze blonde

    What size nib is that??

  • vaccum sealer

    I watch the video,it's awesome. You have done a good job. I got this by

    Best Vacuum Sealer . Thanks for the post.