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Physics of diving with a "straw"

Discussion in 'Basic Scuba' started by kgallowaypa, May 1, 2014.

  1. kgallowaypa

    kgallowaypa DIR Practitioner

    # of Dives: 25 - 49
    Location: Miami, Florida, United States
    I know this might be an odd question, and I think I understand the reason why it can't be done for deep dives, but just wanted to make sure. (brainfart)

    Thought problem:

    If a diver wanted to go deep and had a hose that somehow was able to extend as he descended but while still having the other end of the hose at the surface, allowing him to breathe air at 1ATM, what would happen to the diver at depth?

    So I understand that the deeper you go the pressure increases relative to the depth you are breathing the air from in ATM' pressure. Im assuming the pressure to breathe from depth up to the surface would make it almost impossible to breathe at even 30m. Just wondering out of curiosity, coworker asked me this question and I didn't know what to say haha. So would the diver be even able to breathe? The idea of surface-supplied diving comes to mind but this is just a thought problem with a magical hose.
  2. rx7diver

    rx7diver Solo Diver

    One problem with overly long or large snorkels is, a diver will necessarily be re-breathing his own exhaled air. This is in the case of snorkels only mere inches longer than or fractions of an inch larger (internal cross-section) than "standard" snorkels. Even if the diver could actually breathe, he/she wouldn't be able to breathe much, if any, *fresh* air. This is the first problem, I think.

    Safe Diving,

  3. soccerrefjason

    soccerrefjason Regular of the Pub

    # of Dives: 25 - 49
    Location: Near Daytona Beach Florida
    The Science Of Straws - Mr. Wizard's Challenge - YouTube

    ehhh not exactly what you asked for.... but the reverse...

    I believe the weight of the pressure or atmospheres you are underwater will adversely affect your ability to draw a breath through a magical hose. unless its dark magic. Then there is the issue of air volume... At some point the volume of air that the hose contained would be greater than that which the diver could inhale. That would cause the diver to inhale his own exhaled air. If the diver removed his mouth from his magical extending hose in order to exhale then water would rush into the opening. It is also important to consider material when constructing magical hoses. If the hose were made out of a plastic straw type material then the low pressure created by the sucking of the breath through it would likely cause the hose to collapse under the pressure of the water on the outside of it.

    I am not a scientist nor am i very good at sentence structure or grammar.

    I hope you find my response either helpful or humorous.
    kgallowaypa likes this.
  4. Dr. Lecter

    Dr. Lecter Solo Diver

    # of Dives: 500 - 999
    Location: NYC/Honolulu
    Let's assume the diver was smart enough to try to exhale through their nose, and just focus on the fact that they'd be trying to expand their lungs with 1ATA of pressure while fighting several ATA of water pressure compressing their chest. Perhaps someone with serious breath training and diaphram strength could overcome some water pressure and expand their lungs regardless, but basically you cannot breathe in gas that is at a much lower pressure than the water that is compressing your lungs.
    eelnoraa, KeithG, agilis and 4 others like this.
  5. rx7diver

    rx7diver Solo Diver

    Gotta be able to exhale into the snorkel to purge it of any water that enters it.
  6. oly5050user

    oly5050user Dive Travel Professional

    # of Dives: 5,000 - ∞
    Location: Westchester NY
    aint going to happen. try it with a snorkel that is as short as 3'..as you exhale you will definitely feel the air rush out of you , try to inhale and you will find it next to impossible at as shallow a depth of 3ft.
    over 30 years ago in a NASDS course we had a short length of hose attached to a jet snorkel to demonstrate how pressure at a depth as shallow as 3ft would make this next to impossible..was good for a few laughs in the pool.
  7. scagrotto

    scagrotto Contributor

    # of Dives: 500 - 999
    Location: Hudson Valley
    Almost every word of that post makes me wonder if you understand the diving physics from your OW class.

    I hope you know that any air the diver inhales has to be at the same ambient pressure as the diver, and that a diver at 5' isn't breathing "air at 1ATM".

    You understand that the only reason that surface supplied diving works is because the air is compressed, and delivered at the diver's ambient pressure? Most importantly, do you understand that the location of the air source is irrelevant, and that if you held your breath and ascended after inhaling surface supplied air you'd die exactly the same way as if you had inhaled from a tank on your back?

    If you're really curious, you can probably get a vacuum gauge for $20 at your local auto parts store. If you can pull more than 2 to 3 PSI you should probably call the folks at Guinness to see if that's a category they;'re tracking.
    captain and oly5050user like this.
  8. swimmer_spe

    swimmer_spe Contributor

    # of Dives: 50 - 99
    Location: Sudbury, Ontario
    Lets say it is a 2 tube design such that no matter what, you exhale through one and inhale through the other.

    Eventually you would run into 2 problems.

    1) air pressure. You would eventually not have enough strength to overcome the air pressure to exhale.

    2) water pressure. The water pressure would be such that you cannot breath in enough due to the water pressure preventing your chest to move.
  9. oly5050user

    oly5050user Dive Travel Professional

    # of Dives: 5,000 - ∞
    Location: Westchester NY
    You have it wrong about exhaling..you start to exhale into an area that is lower pressure, such as a extra long snorkel, and your exhalation goes out real fast. Try to fill a paper bag with air and then squeeze it real fast.
    As to inhaling, you cannot suck in hard enough to overcome the higher ambient pressure and bring down the lower pressure air from the top of the snorkel from as little as 3-4ft of depth.
    Last edited: May 2, 2014
  10. Hickdive

    Hickdive Solo Diver

    # of Dives: 1,000 - 2,499
    Location: Glasgow, UK
    Take a regular snorkel, hang onto the side of the pool and, whilst breathing through the snorkel, hold your head underwater so it is completely submerged but the tip of the snorkel is still above the water.

    If you can draw air down at all you're doing well, if you can draw air down in a normal breathing pattern for any length of time time then you are doing extremely well.

    As noted though, this is very, very basic stuff that should have been covered in whatever entry-level course you did. After all, if the technique worked there would be absolutely no need for cylinders, compressed air, regulators etc.

    Here's an extreme illustration of what the pressure differential between being underwater and atmospheric pressure at sea level can do;

    Searcaigh likes this.

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