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Thread: One way valves not so one way.

  1. #1
    Brenton
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    One way valves not so one way.

    Recently bought a Vac a Vin unit for getting air out of opened wine bottles. I experimented with the little pump on the one way valves of my coffee storage bags and guess what.........they are not one way as advertised. Anyone else have this problem?

  2. #2
    Senior Member level3ninja's Avatar
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    How much pressure was required to force the valve to open to let air in? They will have a failure point. I find when I seal my lips around the valve and blow it doesn't let any air in.
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  3. #3
    Senior Member Yelta's Avatar
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    Never had a problem, very much doubt they were designed to be evacuated with a pump, hand pressure is all that's needed.
    Last edited by Yelta; 4 Weeks Ago at 06:26 PM. Reason: spelling error
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  4. #4
    Senior Member Barry O'Speedwagon's Avatar
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    I was also curious, and fitted an inverted bag to the exhaust pipe of my car. I can confirm a) that it failed and b) that I got burnt.

    Seriously though, they're not designed for the level of pressure applied by a pump fixed to the aperture. And unless I get burgled and the burglar devotes his time to playing havoc with my roasted beans cupboard I reckon we'll be ok.

  5. #5
    Brenton
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    Okay maybe did not explain it very well. I used the pump to remove most of the air from the bag and when I took the pump off the valve it leaked air back into the bag. I thought the valve was designed to be only one way and only let gas / air out of the bag, not in ?.

  6. #6
    Senior Member level3ninja's Avatar
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    Sounds like you created a vacuum inside the bag, the force of which was greater than the failure point of the valve
    Last edited by level3ninja; 4 Weeks Ago at 07:02 PM. Reason: Wordiness
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  7. #7
    Senior Member LeroyC's Avatar
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    One way valves not so one way.

    Iíd be surprised if it was simply due to pressure equalisation after creating a vacuum inside the bag. I think itís more likely that the force exerted while extracting the air from the bag caused the valve to fail.
    Also how quickly did the bag fill again? If it was fairly quickly then you could be right in assuming the valve failed, but if it took a few hours and the coffee was freshly roasted then it wouldíve just been more CO2 from the beans degassing. This is something that Iíve witnessed before.
    Iíve never had a valve fail, but Iíve had ziplocks and seams fail. Thatís the other possibility - the failure could be in another part of the bag. Have you checked this?

  8. #8
    Super Moderator Javaphile's Avatar
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    Quote Originally Posted by level3ninja View Post
    Sounds like you created a vacuum inside the bag, of which the force was great than the failure point of the valve
    Is the same as:
    Quote Originally Posted by LeroyC View Post
    I think it’s more likely that the force exerted while extracting the air from the bag caused the valve to fail.

    Java "As I read it" phile
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  9. #9
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    It's pretty hard to create a vacuum inside a bag...

  10. #10
    Super Moderator Javaphile's Avatar
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    Quote Originally Posted by MrJack View Post
    It's pretty hard to create a vacuum inside a bag...
    It's very easy to create a vacuum in a bag when you are using a vacuum pump, which is exactly what badbudgie did.

    Quote Originally Posted by badbudgie View Post
    Recently bought a Vac a Vin unit for getting air out of opened wine bottles. I experimented with the little pump on the one way valves of my coffee storage bags and guess what.........they are not one way as advertised. Anyone else have this problem?

    Java "No vac!" phile
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  11. #11
    Senior Member LeroyC's Avatar
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    One way valves not so one way.

    I think weíre splitting hairs here. Technically MrJack is correct as from a scientific point of view it wonít actually be a vacuum inside the bag as there will still be some gaseous matter in there (along with the coffee of course). In lay terms it will however function like a vacuum in regards to the sealed environment having a large pressure differential to the outside environment (and the fact that a vacuum pump was used to create it). Either way it sounds like these particular coffee bags, if not most, arenít up to withstanding this sort of treatment. So itís probably best not to do this and itís probably unnecessary anyway.

  12. #12
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    Quote Originally Posted by Javaphile View Post
    It's very easy to create a vacuum in a bag when you are using a vacuum pump, which is exactly what badbudgie did.




    Java "No vac!" phile
    Not when you only remove "some of the air", you can't.

    The air inside stays pretty much in pressure equilibrium with the outside (because the bag collapses). It might be slightly below atmospheric due to some resistance of the bag to collapse, but it's unlikely to be a large pressure differential unless you have pretty much flattened the bag (and even then...).
    Last edited by MrJack; 3 Weeks Ago at 10:13 AM.
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  13. #13
    Super Moderator Javaphile's Avatar
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    If you want to split hairs then technically there is no such thing as a vacuum, only a partial vacuum. Vacuum is defined as the absence of all matter. Even ignoring the presence of things like neutrinos, gamma rays, cosmic rays and dark matter outer space (The area between the planets/stars/galaxies.) is only a partial vacuum as it contains a handful of hydrogen atoms per cubic meter. In engineering, applied physics, and common usage a vacuum is an area/volume where the pressure is lower than atmospheric pressure or in the case of a container the area around it. By that definition with any pressure differential between two areas the one with the lower pressure is considered to be a vacuum, no matter how small that difference is.


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  14. #14
    Senior Member chokkidog's Avatar
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    Vacuum or no vacuum, I'm still waiting on the OP's reply to LeroyC's question in post #7......

    Storm in a coffee bag........

    And after packing over 20 tonnes of coffee in one way valve bags, over 5 years, I have never knowingly had one fail.
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  15. #15
    Senior Member LeroyC's Avatar
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    Quote Originally Posted by chokkidog View Post
    Vacuum or no vacuum, I'm still waiting on the OP's reply to LeroyC's question in post #7......

    Storm in a coffee bag........

    And after packing over 20 tonnes of coffee in one way valve bags, over 5 years, I have never knowingly had one fail.
    Yeah agreed. Letís eliminate other possible failure points before we worry too much about the valve.
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