Fast leaking CO2?

neeb
neeb Posts: 4,473
edited May 2016 in Workshop
I'm a relatively recent convert to CO2 inflators for roadside punctures. I use ultralight butyl tubes (Contenental Race Supersonic, the 50g ones - IME they ride better as well as being lighter, more like latex but without the slow leaking issue).

So the other day I had a pinch flat, swapped the tube on the road, inflated with C02 and cycled 20 miles home without issue. Next time I checked (2 days later?) the tyre was completely flat. Suspected a slow puncture caused by careless fitting of the tube on the road (the tyre / rim combination is really unusually tight, a right PITA), but for the life of me I can't find the slightest hint of one, and I'm quite good at spotting even the smallest leak under water.

I've heard that CO2 can leak faster than air from tyres, something to do with CO2 dissolving in butyl... Is it possible that in a 50g butyl tube (considerably thinner than normal) the C02 could have leaked out completely in the course of a couple of days without there being a puncture? With air they remain solid for weeks.

Comments

  • sungod
    sungod Posts: 17,496
    yes

    as you say, carbon dioxide dissolves in butyl rubber, this results in rapid loss of pressure

    this goes much faster than the diffusion process through which air escapes
    my bike - faster than god's and twice as shiny
  • sniper68
    sniper68 Posts: 2,910
    If you use Co2 out on the road you should always deflate the tyre and use a pump to re-inflate the tyre once you get home.Co2 is a temporary fix.I've never actually left it to see how quick the tyre loses pressure,over night seems a bit quick,but it will lose pressure much faster than it would if pumped up the conventional way.
    Lynskey R480

  • neeb
    neeb Posts: 4,473
    All makes sense, thanks!

    Put some air in the tube last night, left it hanging on a door knob and it's exactly the same this morning, so it must have been the CO2. It was a brand new tube (so lots of CO2 absorption capacity in the butyl?) and as I say, pretty thin rubber, so I guess that accelerated the CO2 loss. Quite dramatic really!
  • ugo.santalucia
    ugo.santalucia Posts: 28,335
    sungod wrote:
    yes

    as you say, carbon dioxide diffuses in butyl rubber, this results in rapid loss of pressure

    this goes much faster than the diffusion process through which air escapes

    FIFY
    left the forum March 2023
  • sungod
    sungod Posts: 17,496
    ugo.santalucia wrote:
    sungod wrote:
    yes

    as you say, carbon dioxide diffuses in butyl rubber, this results in rapid loss of pressure

    this goes much faster than the diffusion process through which air escapes

    messed that up for you

    FTFY

    as i correctly stated, diffusion is the process by which air escapes, a different mechanism to that which dominates the escape of carbon dioxide

    carbon dioxide is soluble in butyl rubber, it dissolves into it chemically, permeating the material and escaping
    my bike - faster than god's and twice as shiny
  • ugo.santalucia
    ugo.santalucia Posts: 28,335
    sungod wrote:
    ugo.santalucia wrote:
    sungod wrote:
    yes

    as you say, carbon dioxide diffuses in butyl rubber, this results in rapid loss of pressure

    this goes much faster than the diffusion process through which air escapes

    messed that up for you

    FTFY

    as i correctly stated, diffusion is the process by which air escapes, a different mechanism to that which dominates the escape of carbon dioxide

    carbon dioxide is soluble in butyl rubber, it dissolves into it chemically, permeating the material and escaping

    I woud not contraddict me on this if I were you, but fair enough, it's irrelevant to the topic
    left the forum March 2023

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