Re: [CR] Pennine CO2 Tire Inflators - Calculation Whoops!

(Example: Humor)

From: "Scott Minneman" <minneman@onomy.com>
To: 'Hugh Thornton' <hughwthornton@yahoo.co.uk>, 'Classic Rendezvous' <classicrendezvous@bikelist.org>, 'Stevan Thomas' <NortonMarg@aol.com>
References: <755674.25335.qm@web25906.mail.ukl.yahoo.com>
In-Reply-To: <755674.25335.qm@web25906.mail.ukl.yahoo.com>
Date: Mon, 27 Apr 2009 14:57:28 -0700
Organization: Onomy Labs, Inc.
Thread-Index: AcnHfCqEmrpFR8WNSQqh54JE6rF4jgAAX0iQ
Subject: Re: [CR] Pennine CO2 Tire Inflators - Calculation Whoops!


I'm pretty sure that you've looked at the phase diagram incorrectly, and that CO2 with be a gas over liquid at 900psi at or about room temperature. The cartridge thus requires that you use the good old Ideal Gas Law (pV=nRT) with that 8g of CO2 rather than the simple volume/pressure ratio calculation you used.

Back of the envelope says a 12g cartridge should yield a little over 90psi with a road tire. A 16g cartridge will fill the same tire to 120psi or so. An 8g cartridge will not deliver enough pressure to make you very happy (60-ish psi), but it'll probably get you home. Two of them will make you happier (or a modern one with more CO2, if it'll fit).

Scott Minneman ...seeing more chill and wind than usual in... San Francisco, CA - USA

-----Original Message----- From: classicrendezvous-bounces@bikelist.org [mailto:classicrendezvous-bounces@bikelist.org] On Behalf Of Hugh Thornton Sent: Monday, April 27, 2009 2:07 PM To: Classic Rendezvous; Stevan Thomas Subject: Re: [CR] Pennine CO2 Tire Inflators - Calculation Whoops!

Before you all rush to point it out, I meant to say that the volume of a tire is about 800cc or about 80 (not 800) times the volume of the inflator cartridge, but the pressure in the tire was worked out using the correct value and so is still not much more than 10psi.  Sorry. Hugh Thornton Cheshire, England


--- On Mon, 27/4/09, Hugh Thornton wrote:


From: Hugh Thornton <hughwthornton@yahoo.co.uk> Subject: Pennine CO2 Tire Inflators To: "Classic Rendezvous" <classicrendezvous@bikelist.org>, "Stevan Thomas" <NortonMarg@aol.com> Date: Monday, 27 April, 2009, 9:45 PM

A couple of weeks ago, Stevan Thomas was asking about CO2 cartridges for a Pennine inflator.  These were nicely made aluminum inflators that used CO2 cartridges the same as used in Soda Siphons - there were several brands but the best-known in the UK was, I think, Sparklets.  I believe that similar siphons using the same cartridges were available in the US.

Since then I have discovered that cartridges are still available in the UK and there is quite a market for retro soda siphons.  This really interested me because I have one of these inflators which I acquired together with a few old cartridges, and I used it once, on a fairly narrow sew-up, to see how it would work.  It was almost completely useless, inflating the tire to a low pressure and not saving me much manual pumping.

Finding the cartridges still available, I checked the specification and saw that they contain 8gm (10cc) of CO2 at 900psi (but it doesn't say what temperature gives that pressure, so I assume about 18degC).  I then calculated that the volume of a tire is about 800 times the volume of the cartridge.  Looking at a phase diagram of CO2, it will not liquify at 900psi at 18degC so it seems reasonable (to me anyway) to assume that Boyle's Law applies and that Pressure x Volume is constant (once everything is back to the same temperature).  On this basis, 10cc at 900psi expanding 800 times gives a pressure not much better than 10psi.  Which seems to confirm my impression that these inflators aren't much good unless you have a pocketful of cartridges and almost as much time to spare as it would take to inflate the tire with a pump.

So my question is, does anybody out there have contemporary experience of these inflators?  I would be really interested to know whether people's experience in the 1950s stacks up with my experience with an old cartridge (which just may have lost pressure) and with my calculation (which may well be flawed - perhaps someone can tell me whether I got it right or totally wrong).

In my youth I had a very fancy CO2 (or was it nitrogen?) inflator of the sort you sometimes see in photos of Coppi and other riders of the era.  It was activated by screwing the cylinder in its end piece which housed the push on connector for the tire valve.  My recollection is that these were made by Edco and they were well able to inflate a tire.  Can anyone confirm that, and are they ever seen these days?  These things were really quite heavy, so one has to feel sorry for those professionals who had to ride their bikes up huge mountains often on bad surfaces.  Many of the frames themselves weren't too heavy of course, but add all the things like steel cranks and gears, clamp on steel bottle cages with full bottles, heavy inflators and a few spare tires and the total weight would be quite daunting.  Those guys were really heroic.

Hugh Thornton
Cheshire, England