Why does my new LAMY cp1 have a hole in the cap?

[tmurfet]

Enquiring minds need to know, there is also a slot under the clip that has no known purpose I can figure out...

[silverlifter]

So that when you uncap the pen, there isn't a vacuum that sucks a blob of ink out onto your page/pants.

[tmurfet]

That’s what I figured, there remains the question: as a result of the hole, does the nib dry out more quickly than my Rotring Esprit that has no hole but stays wet for weeks?

[silverlifter]

No, the hole is set much further back, so there will either be an inner housing to seal the section, or some other means of ensuring the nib itself is in an airtight enclosure. Shine a light into the cap and it should be clear how it works. Lamy has been doing this for a long time; they won't have missed something so obvious.

[A Smug Dill]

1 hour ago, silverlifter said:

Shine a light into the cap and it should be clear how it works.

 

Actually, I'm finding it difficult to follow the logic. If there's an airtight enclosure around the nib and feed when the pen is capped, then if the user removes the cap quickly enough it'll create an expanding space in which, for a brief moment, the air pressure is lower than that inside the pen's ink reservoir before air rushing into the breach of that formerly airtight enclosure has time to equalise the pressure. If the hole, without being a one-way valve, is there to allow equalisation of air pressure inside the cap at all times, then surely air must be able to flow in and/or out of the enclosure around the nib and feed when the pen is unused.

 

Or are you saying that, when the pen is capped, there are two enclosures inside the cap, completely separated by the inner plastic cap, and any breather hole in the exterior shell of the cap is only there to allow air pressure equalisation for the outer enclosure?

[silverlifter]

52 minutes ago, A Smug Dill said:

Or are you saying that, when the pen is capped, there are two enclosures inside the cap, completely separated by the inner plastic cap, and any breather hole in the exterior shell of the cap is only there to allow air pressure equalisation for the outer enclosure?

Likely this. But I don't have that model pen, so that's why I phrased it as conjecture. The smaller the sealing chamber, the less likely there will be sufficient force to draw ink from the feed.

[pearlfox]

The big one's for sticking your pen into.

 

52 minutes ago, A Smug Dill said:

Actually, I'm finding it difficult to follow the logic.

https://fountainpendesign.wordpress.com/cap-fountain-pen-history-overview/57-2-caps-mechanics-and-physics/

 

[corgicoupe]

I'll say again, Amadeus W's site ought to be required reading, as it answers soooo many questions that tend to get raised here on FPN.

[tmurfet]

16 hours ago, tmurfet said:

That’s what I figured, there remains the question: as a result of the hole, does the nib dry out more quickly than my Rotring Esprit that has no hole but stays wet for weeks?

Thank you pearlfox for providing the link to https://fountainpendesign.wordpress.com/. I enjoy the discussion here. The Esprit cap doesn't appear to have a hole, the inner cap (looking similar in shape to the LAMY cp1 example used by Amadeus W) appears to snap and seal at the front end of the grip. The design of the Rotring feed and nibs (sans the usual nib hole) is another topic for discussion.

Cheers!

[A Smug Dill]

On 3/21/2021 at 2:52 PM, pearlfox said:

https://fountainpendesign.wordpress.com/cap-fountain-pen-history-overview/57-2-caps-mechanics-and-physics/

 

Thanks for that; but I just don't get it, unless the pen's gripping section is flush with the interior surface of the bottom half (closest to the opening) of the cap and there is no other way for air to escape when capping; which does not appear to be the case with the Lamy cp1.

[tmurfet]

Perhaps the inner cap is slightly compressed when the cap is snapped to the barrel. So that when removing the cap, the small volume inside the inner cap is repressurized after the cap is unsnapped. While when snapping the cap to the barrel the small volume is repressurized first, and so: reducing the pressure change effect on the nib section. The hole is there because otherwise the nib section would be pressurized to a higher level prior to the inner cap engaging/dissengaging. For the Esprit, I'm convinced the same principle applies except that there is no hole, and in comparing to the LAMY; no, or very little pressure seal where the cap engages to the barrel. Further, the Esprit cap doesn't actually engage to the barrel, there is usually a tiny gap (the cap easily spins around unless the pen is new). 

[pearlfox]

On 3/22/2021 at 2:28 AM, A Smug Dill said:

Thanks for that; but I just don't get it

My fluid dynamics is a bit rusty these days (air is a compressible fluid), but I believe it's not just the area of the openings at play, but the distance over which air must travel in those confined spaces, with a small but short hole (tube) close to the inner cap's opening providing less resistance--and thus reduced pressure differential--than the more distant outer cap's opening with the pen section's obstruction taken into account.  There's also a lot less air in the cap with the pen fully inserted, making the initial movement more sensitive; so as the pen's removed further from the cap, the cap's main opening becomes less constricted, the total volume of air increases, and pressure differential reduces.

[two2tone]

Holes in pen caps are there to prevent choking when swallowed.

 

https://tiphero.com/holey-pen-caps

 

 

[silverlifter]

1 hour ago, two2tone said:

Holes in pen caps are there to prevent choking when swallowed.

 

https://tiphero.com/holey-pen-caps

 

 

 

Holes in fountain pen caps long predate that Bic design element...