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Thread: Pressure

  1. #1
    Established TDF Member Paul r s's Avatar
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    Pressure

    Whilst driving home this evening I had a thought that I wasn't sure of the answer.
    Obviously I'm aware of pressure underwater etc.

    but (for example)
    (1) if I took my camera housing down to 20m and had an old analog depth gauge inside would the needle move

    (2) what about in your drysuit ? Because wouldn't the drysuit surround you in an neutral atmospheric pressure

    (3) if neoprene gloves worn under dry gloves (bungee installed to allow air to migrate), as you descend would the neoprene begin to compress

    (4) if a 40m rated camera housing was installed with its only gas supply that acted the same way as an adv and opv from a breather. Would it then be able to go much deeper ?

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    Closed Account: User Requested nickb's Avatar
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    1) No
    2) Yes - No, it's ambient
    3) Yes
    4) Yes - but.....
    Last edited by nickb; 15-01-2013 at 08:33 PM.

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    Administrator Garf's Avatar
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    Quote Originally Posted by nickb View Post
    1) No
    2) Yes - No, it's ambient
    3) Yes
    4) Yes - but.....
    lol, good answer.
    Gareth Burrows
    Having a break from teaching divers.
    www.divedir.com

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    Coastal Member dwhitlow's Avatar
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    Agreed with 1-3 but

    4) not relavent,.

    the depth rating of cameras is the depth at which they will work as specified. this will go deep but buttons might stick.
    (my 40m rated camera housing worked flawlessly at 70m)

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    Established TDF Member Paul r s's Avatar
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    Wouldn't the pressure in the gloves be 1bar, meaning the neoprene gloves wouldn't compress ?

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    Established TDF Member Barrygoss's Avatar
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    Pressure

    Quote Originally Posted by Paul r s View Post
    Wouldn't the pressure in the gloves be 1bar, meaning the neoprene gloves wouldn't compress ?
    Dry gloves, a bag if air round your hands. At ambient pressure
    B
    Rebreathers are like women; they pretend to love you, whilst taking all your money and trying to kill you.

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    Closed Account: User Requested nickb's Avatar
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    I'll expand on the short answers above:

    1) Think about Boyle's Law - the volume remains constant (pretty much, it may change minutely), therefore the internal pressure will remain constant. Which is what we desire from a camera housing. A depth gauge measures depth indirectly - what it actual measures is the relative change in pressure. In this case, none - therefore no depth change.

    2) When we descend, we need to add gas to our suit in order to maintain the volume of the suit and prevent squeeze, which is uncomfortable and reduces thermal insulation. If you were to ascend from 10m to the surface with the suit valve shut, the volume of gas inside the suit would double. It's the pressure that keeps the gas volume reduced, Boyle's Law again. The pressure inside the suit is the same as the pressure outside the suit, i.e. ambient. Therefore the gauge would show the correct depth.

    3) The gloves would compress for the same reason that the depth gauge would register the actual depth, they are responding to the ambient pressure. The gas surrounding them is having the exact same effect as the water would if the dry gloves weren't there.

    4) The vulnerability of a camera housing will be in the integrity of the housing body or, more likely, the o-rings and buttons. If the pressure inside can be equalised with the outside water pressure in the same way as the dry suit above, that weakness is eliminated. This is why a CCR can be taken to extreme depths without the hoses collapsing. The problem with operating a camera housing like this would be the camera itself. Clearly, raising the pressure at which the camera is operating will ultimately cause a problem with the camera itself.

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    Red Hot Totty ;) Hot Totty's Avatar
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    Yet again nick beats me to the answer

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    Coastal Member dwhitlow's Avatar
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    Quote Originally Posted by Hot Totty View Post
    Yet again nick beats me to the answer
    getting slow are we?

  10. #10
    Red Hot Totty ;) Hot Totty's Avatar
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    Quote Originally Posted by dwhitlow View Post
    getting slow are we?


 
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