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Testing Empty Housing

Discussion in 'Tips and Techniques' started by divinh, Sep 7, 2018.

  1. divinh

    divinh Photographer

    # of Dives: 100 - 199
    Location: San Francisco
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    I dropped my GoPro, in housing, on concrete, just a few hours ago and I feel so stupid, as it was precariously placed when I was handling it. I hope it's still structurally sound... :(
     
  2. Diving Dubai

    Diving Dubai Instructor, Scuba

    # of Dives: 500 - 999
    Location: Dubai UAE
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    ^^^^ Not true

    With respect. The Air inside an empty housing will stay at the pressure that it was when it was last opened. The housing may deform slightly but this will have a negligible effect on the gas volume inside and thus pressure. That's the whole point of housings to withstand the outside water pressure. Some like Go-Pro housings may be designed to used the cameras as a structural support, others do not.

    The only time you will have a negative pressure is if you open and close it on an aircraft or at altitude and then try to open it at sea level where the greater outside pressure will prevent it.
     
    peterak likes this.
  3. stepfen

    stepfen Barracuda

    # of Dives: 200 - 499
    Location: Greece
    456
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    I second that.
    To the OP think about it like this: How a camera that is made for surface use (1ATM) is supposed to help a case withstand 5 or so ATM???
    Would you like to put a pressure of 1-2-3ATM directly on your camera?
    The case should be able to withstand bottom pressure without putting any pressure to the camera itself hence no matter whether the camera is in the case or not.
     
  4. giffenk

    giffenk Great White

    # of Dives: 500 - 999
    Location: toronto
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    I think we have mixed 2 seperate concepts and confused the situation.

    1: camera as structure. it is possible that some housings do this by placing pads near the edges of the camera body. Normally these pads are to hold the camera in place (for those housings that do not use a saddle). The frame of the camera is very strong compared to the lens / buttons / screen. Some (cheap?) housings may actually rely on this little bit of extra support midway along the housing door? A design like this would worry me.

    2: empty vs full housing. no difference in ability to withstand pressure. The door only needs to bend an extremely small amount before the oring sealing surface is deformed enough to cause a leak. Even with a camera installed the remaining airspace is large enough for a flimsy door to bend. No housing depends upon the air pressure inside the housing to prevent a collapse. The current trend of using vacuum leak detectors provides a good example of this.
     
  5. caruso

    caruso Banned

    # of Dives: 200 - 499
    Location: Long Island, NY
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    You referred to my post as being incorrect, then substantiated your post by saying the camera does not provide structural support- which is true- and is not what my post was about. My post is all about the larger air space in an empty housing compressing and causing a much higher degree of negative pressure = a vacuum inside a camera housing than the much smaller amount of airspace when a camera is filling almost the entire compartment.
     
  6. Diving Dubai

    Diving Dubai Instructor, Scuba

    # of Dives: 500 - 999
    Location: Dubai UAE
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    Seriously. You're just talking nonsense.
     
  7. stepfen

    stepfen Barracuda

    # of Dives: 200 - 499
    Location: Greece
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    As explained above the tiny deformation the case might have causes very small difference (if any) at the total volume of the case, hence the pressure of the air inside it even at depth should still be 1ATM (or whatever was the ambient pressure when the case was closed).

    No matter what is inside the case there are two cases:
    a) The casing is strong enough to withstand the pressure by itself, or
    b) The casing is not strong enough and needs "help" from whatever is inside it.

    In case a) the camera and the integrity of the case are always "safe" (within safe depth limits) - no matter what is inside them. I would bet my money that all/most the good quality camera cases are made like this.

    In case b) whatever is inside the case needs to be exposed and withstand at least part of the external pressure. I wouldn't expose delicate equipment (eg expensive cameras) to external pressures on purpose.

    I don't know if Chinese make such cases. What I know is that I have brought several times both my crap fake-gopro cases (the one that came with my camera and the 3 dollars one bought from ebay) and my meikon case for my sony a5100 camera with me to depths down to 80-100 feet empty or with just a tissue inside them for leak tests without any problems.
     
    giffenk likes this.
  8. giffenk

    giffenk Great White

    # of Dives: 500 - 999
    Location: toronto
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    your post is incorrect.

    The housing is inflexible. It is rigid (for all practical measurements). The housing does not compress. The contents inside the housing do not compress. The pressure inside the housing will always be 1ATM regardless of its contents or depth. Full of air, or full of camera and air. The pressure inside the housing will remain what it was when you closed the door. The contents do not matter.

    But, some people use a vacuum leak detection system. Then the pressure inside will be less than 1 ATM but will not change as you go deeper because the housing is inflexible. Regardless of whether there is a camera in the housing.

    The pressure differential between the inside and outside of the housing will increase as depth increases. The outside pressure increases, the inside pressure stays the same. Increasing depth will put more stress on the housing. A vacuum leak system will create more stress than a housing without it.

    Increasing depth does not change the pressure inside the housing since the housing does not compress. So it does not matter what is inside the housing - unless the housing is a POS and depends upon the camera for structural soundness.
     
  9. caruso

    caruso Banned

    # of Dives: 200 - 499
    Location: Long Island, NY
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    It's not intended to decompress under normal usage. Meaning that when it's brought to depth, with most of it's inner volume filled with a camera, it can handle the stress of the negative pressure. If the housing is not intended to be brought to depth empty, then it can and very well may compress to the point that at the very least the seal doesn't hold and at worst it breaks.
     
  10. stepfen

    stepfen Barracuda

    # of Dives: 200 - 499
    Location: Greece
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