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Why do fountain pens leak in planes?


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#1 brabus

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Posted 03 February 2009 - 22:43

I know a fair bit of science but I never understood why fountain pens sometimes leak in plane cabins. If the pen has an air pocket in the reservoir, then shouldn't a higher pressure force the ink out and not a lower pressure, the kind you'd find in a plane cabin?



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#2 HDoug

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Posted 03 February 2009 - 22:53

As the cabin depressurizes, the air bubble inside the reservoir expands forcing the ink out. That's why those awful buns (or whatever they are) that are wrapped in plastic look like packing insulation at altitude even though they are well behaved on the ground.

Doug

#3 someonesdad

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Posted 03 February 2009 - 23:05

The problem is that the air bubble behind the ink in the cartridge/converter/piston is at your local atmospheric pressure. When you get on a plane, it's common for the pressurized cabin's air pressure to be lower than the ambient pressure at the airport. This causes the air bubble to expand and force ink out. The solution is simple -- keep the tip of the pen pointed up so there's no ink behind the bubble.

#4 brabus

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Posted 03 February 2009 - 23:27

Thanks for the reply, this really helped.

#5 gyasko

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Posted 03 February 2009 - 23:58

Just to put some numbers on it, the air pressure inside a plane at cruising alt. is about 750 hPa. On a nice day on the ground, the pressure might be 1000 hPa.

#6 wykpenguin

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Posted 04 February 2009 - 01:15

I have read somewhere that planes are pressurized to the air pressure of about 3000ft above sea level.

#7 blackranger63

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Posted 04 February 2009 - 01:39

There is a very good thread on flying with fountain pens that covers a lot of good ground. I recently traveled to Turkey and back again with four different pens and NONE leaked in the air. And I used them all (Pilot VP, Pelikan 140, Sheaffer Skripsert Black and Gold Tulle, and a lowly (smile) Wearever Pennant) without issue. The Pennant did finally develop seepage when I landed on my last flight in Norfolk, but I think that was because the ink was really low since I used it a lot in Turkey and did not take extra ink. The VP is a Beast. It takes whatever I dish out and comes back for more.

Cheers,

Tony
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#8 BillLS

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Posted 04 February 2009 - 04:36

QUOTE (wykpenguin @ Feb 3 2009, 05:15 PM) <{POST_SNAPBACK}>
I have read somewhere that planes are pressurized to the air pressure of about 3000ft above sea level.


I've worked as a Boeing engineer for 43 years so believe me when I tell you that the correct number is closer to 8000 feet than 3000. The new 787 Dreamliner will be better, we can keep the cabin altitude down to 6000 feet.

Bill Sexauer
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#9 solitaire

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Posted 04 February 2009 - 14:08

Yes keep nib upwards and the expanding air goes directly out through the nib.

Having an ink reservoir that is completely full means no expanding air and no leaks.

The VP is well-behaved because the reservoir is so small.

Manufacturers like carts because with small amounts of ink the problem isn't so bad (the collector can hold the excess)

Therefore watch out for half filled MB 149s and/or M 1000s with nib down.
Solitaire

Edited by solitaire, 04 February 2009 - 14:09.


#10 Johnny Appleseed

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Posted 04 February 2009 - 15:54

QUOTE (sexauerw @ Feb 3 2009, 08:36 PM) <{POST_SNAPBACK}>
QUOTE (wykpenguin @ Feb 3 2009, 05:15 PM) <{POST_SNAPBACK}>
I have read somewhere that planes are pressurized to the air pressure of about 3000ft above sea level.


I've worked as a Boeing engineer for 43 years so believe me when I tell you that the correct number is closer to 8000 feet than 3000. The new 787 Dreamliner will be better, we can keep the cabin altitude down to 6000 feet.



That is my understanding as well.

The main issue is stress on the airframe. If you tried to keep an average plane pressurized to 3000 ft, the pressure difference would be to great at 30,000ft and the cabin would burst like a giant balloon - not pretty.

John
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#11 psfred

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Posted 04 February 2009 - 16:03

Any time there is a pressure difference between the air in the ink reservoir and the outside, ink or air will move to the lower pressure area. If the pen is nib up and the air pressure is lower, air will come out the breather hole in the nib (or in the case of nibs with no hole, where ever the air breather hole is in the feed). If the nib is down, so that ink covers the feed on the reservoir end, ink will come out instead. This makes a mess, and NO fountain pen held nib down while the air pressure outside the pen is falling will fail to drip ink, including a Parker "51" aerometric if enough ink is forced out to flood the collector.

Ditto for picking up a very cold pen and starting to write with it -- my Parker 61 burped up on me the other day. It lives in a box on my desk, but the desk is next to a window in a poorly heated room and it was well below hand temperature. A couple minutes into a letter and it dropped a nice blot on my page.

As for aircraft, the only one I know of that was "fully pressurized" was the original DeHavilland Comet, which blew apart in the air from the repeated stresses of changing pressure and a fatigue failure event (not related to the pressure). The high pressure (9.45 psi) was only part of the problem, but it surely didn't help matters any. The revised version got a new fuselage structure to prevent "running cracks", a re-design of the window frames (where the actual failure originated from a mis-placed rivet hole) and was only pressurized to 7000 ft, a large reduction from the original sea level pressurization. The Comet 4 was in airline use from the late 1950's to the mid 80's when it got too expensive to fly even for charters.

Peter

#12 DerMann

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Posted 04 February 2009 - 22:49

My "51" leaks every time I fly :/
Collection:
Waterman: 52V BCHR, 55 BCHR
Sheaffer: Peacock Blue Snorkel Sentinel, Black Snorkel Admiral, Persian Blue Touchdown Statesman
Parker: Silver 1946 Vacumatic, 1929 Lacquer red Duofold Senior, Burgundy "51" Special
Misc: Reform 1745, Hero 616, two pen holders and about 20 nibs.

#13 psfred

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Posted 04 February 2009 - 23:13

I've taken mine on three round trips by air, at least one stop-over each time, and never had a leak of any kind. Not with my Sheaffer Snorkels, either.

Peter


#14 I am not a number

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Posted 04 February 2009 - 23:35

QUOTE (sexauerw @ Feb 4 2009, 04:36 AM) <{POST_SNAPBACK}>
I've worked as a Boeing engineer for 43 years so believe me when I tell you that the correct number is closer to 8000 feet than 3000. The new 787 Dreamliner will be better, we can keep the cabin altitude down to 6000 feet.

I have 5,000 flying hours. The 8,000ft figure is what we used on transport aircraft, if there is a pressurisation problem and terrain, airspace or range (fuel burn efficiency considerations) mean that you have to stay high up, then above 10,000 ft cabin altitude the crew go on oxygen, above 15,000 ft the passengers do as well.
It is a truth universally acknowledged, that a single man in possession of a good fortune, must be in want of nothing at all...

#15 WilsonLaidaw

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Posted 22 June 2015 - 18:50

Very occasionally I get to travel in a Gulfstream G550, which is pressurised to 6000 feet and it makes a difference to comfort of travel but more importantly there is no re-circulated air, which is what I feel makes regular airline travel so unpleasant. Last year my wife and I flew from Dubai to Bangalore in a 787 Dreamliner and it was noticeably more comfortable than other planes. My usual Mont Blanc Bohême retractable nib, with cartridge filling has never leaked in a plane but I have posted in another thread to ask if my recently acquired (but recently rebuilt by Dr. Oldfield) Sheaffer Snorkel will leak on a flight to the USA next week. I prefer writing with the Snorkel to the Bohême. 

 

Wilson








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