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SCUBA question


Alpo

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Does the air only come out of the tank when you are inhaling?

 

Watching Up Periscope. James Garner is going out the escape hatch on the sub, and will swim to the Japanese held island.

 

As the water is starting to flood the escape hatch, he reaches over his left shoulder and appears to be opening a valve. I assumed he was turning the air on in his tank. But once he made it to the beach he did not turn the air off.

 

It occurred to me that if the air could get out all the time, whether you were sucking on it or not, you would want to turn the valve off. It would be a bad thing to go back for your tank so you can swim back to the sub and find out that all the air has leaked out.

 

Now this could be simply a movie mistake, or it could be that the air can't go out unless you're inhaling.

 

Which is more likely?

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Haven't gotten bottom time in quite a while, so this is going mostly on memory:

 

Most modern SCUBA uses a single hose two-stage regulator. The first stage is mounted on the tank and regulates the air pressure down from the tank pressure (for most sport diving, a max of around 3,000 PSI), down to somewhere around 125 or so pounds.

 

The second stage is at the mouthpiece, and has a demand-driven diaphragm valve that opens when you suck in on it and the air flows into the mouthpiece.

 

The old-school double-hose regulator (the kind they used in Sea Hunt) had both stages mounted on the tank, with one hose supplying fresh air to the mouthpiece, and the second taking exhaled air back to the regulator where it was exhausted into the water.

 

I've used a double-hose. Once. Darned near drowned before I figured it out because the positioning of the demand regulator makes breathing a little different, and the ability to get a free flow of air at the mouthpiece is very different.

 

The WW II submarine escape devices were called Momsen lungs and were actually rebreathers, not SCUBA. Maybe someone else here has some insight into them. Also, in dive training we learned a technique called 'free ascent' where you rise to the surface just on the air in your lungs. The problem is -- that air expands as you ascend, so you have to exhale as you go up to bleed it off,  or else you risk blowing out a lung.

 

Edited for clarity

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The man that wrote the book, 1957, that the movie, 1959, was based on also wrote a book in 1964. The Survivors. Bunch of Marines are going in a submarine to do a raid on this island, and for some reason I do not recall the submarine is sitting on the bottom and cannot rise again. The COB is setting out little cakes of something all around the room they're in. He says they absorb CO2, but they can only take you so much. And then he makes sure that his 45 is loaded. He says he will not suffocate.

 

The hero of the book flashes back to being a teenager surfing, and a weird friend of his explaining that you were stupid to drown. That you had enough air in your lungs that you could not drown. And the book goes on to explain a free ascent.

 

I thought, as a 14-year-old reading this book in 1968, that that made sense, and might actually be true.

 

1990, and I am helping to inspections at the Navy Dive School. They have a large swimming pool, and they have five tanks that have portholes in the walls, so the instructors can watch the intrepid frogman and see how bad they're screwing up. Neither of these really need inspection. There are also three hyperbaric chambers. Most people know these as "decompression chambers", but hyperbaric is the correct term. Every welded joint in that huge mass of piping needs inspected. The chamber itself needs inspected. Several days work. Then we go outside, and on the other side of the parking lot is this tower. Looks like a grain silo. Round, maybe 30 ft in diameter, and five stories tall. Has a circular staircase going up to the top. Basically it is a 60-ft deep swimming pool. You go in the air lock at the bottom, take off your tank, and go to the surface. A free ascent. This thing is called the FAT tower. It also has a chamber at the top, in case somebody gets bent on the way up. Instead of having to man handle him down 60 ft of circular staircase and then take him across the 50-yard parking lot to get him into the dive school's chamber, they can just shove him in the FAT chamber and take him down to a couple hundred feet, and unbend him.

 

And I thought, "Hey, Mr. White was right". That would be Robb White, the author of the book.

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I well-remember the old double-hose Aqua-Lungs. My dad and mom were early SCUBA divers on Puget Sound, back in the mid-late 1950s. They made their wetsuits at the kitchen table, cutting out neoprene patterns and gluing the seams.

 

Back in those days, you'd often gather a crowd when you were diving; it was still a rarity.

 

We kids ate octopus, cabazon, and lingcod regularly back then.

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11 hours ago, Ozark Huckleberry said:

 

 

The WW II submarine escape devices were called Momsen lungs and were actually rebreathers, not SCUBA.

 

Re-breathers are very different to SCUBA and have a host of issues from max depths to max time of use.

They are very much a Special Forces specialty these days (no bubble trail). 

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To me, the movie mistake is waiting until the chamber is flooding to open your tank.  Pretty late to find out you have a regulator/tank problem.

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On 1/2/2021 at 9:47 AM, Alpo said:

The man that wrote the book, 1957, that the movie, 1959, was based on also wrote a book in 1964. The Survivors. Bunch of Marines are going in a submarine to do a raid on this island, and for some reason I do not recall the submarine is sitting on the bottom and cannot rise again. The COB is setting out little cakes of something all around the room they're in. He says they absorb CO2, but they can only take you so much. And then he makes sure that his 45 is loaded. He says he will not suffocate.

 

The hero of the book flashes back to being a teenager surfing, and a weird friend of his explaining that you were stupid to drown. That you had enough air in your lungs that you could not drown. And the book goes on to explain a free ascent.

 

I thought, as a 14-year-old reading this book in 1968, that that made sense, and might actually be true.

 

1990, and I am helping to inspections at the Navy Dive School. They have a large swimming pool, and they have five tanks that have portholes in the walls, so the instructors can watch the intrepid frogman and see how bad they're screwing up. Neither of these really need inspection. There are also three hyperbaric chambers. Most people know these as "decompression chambers", but hyperbaric is the correct term. Every welded joint in that huge mass of piping needs inspected. The chamber itself needs inspected. Several days work. Then we go outside, and on the other side of the parking lot is this tower. Looks like a grain silo. Round, maybe 30 ft in diameter, and five stories tall. Has a circular staircase going up to the top. Basically it is a 60-ft deep swimming pool. You go in the air lock at the bottom, take off your tank, and go to the surface. A free ascent. This thing is called the FAT tower. It also has a chamber at the top, in case somebody gets bent on the way up. Instead of having to man handle him down 60 ft of circular staircase and then take him across the 50-yard parking lot to get him into the dive school's chamber, they can just shove him in the FAT chamber and take him down to a couple hundred feet, and unbend him.

 

And I thought, "Hey, Mr. White was right". That would be Robb White, the author of the book.

Submarine School  Groton Connecticut, 1982.  I remember doing a 50 ft free ascent.  HoHoHo all the way up.

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The modern “scuba” set up didn’t happen until post ww2, but weren’t navy frogmen using tanks during the war?

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2 hours ago, Captain Bill Burt said:

Submarine School  Groton Connecticut, 1982.  I remember doing a 50 ft free ascent.  HoHoHo all the way up.

NDSTC, Panama City. '89 to, I think '97 was the last year I did an inspection there.

 

Now this is pathetic. I have been searching the entire dang internet, looking for a picture of the FAT Tower. This is the only one I could find. You can see the pretty blue swimming pool. And I circled the tower, because if I didn't know where it was I probably would have missed it.

 

21_big~3.jpg

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On 1/1/2021 at 10:19 PM, Red Gauntlet , SASS 60619 said:

Like 40 says; WWII would have been before regulated compressed-air systems. I believe Cousteau's Aqua-Lung was the first.

 

Actually Cousteau basically stole the patent from Georges Commeinhes. The Commeinhes family had several patents for on demand regulators supplied via high pressure air tanks. Initially they were developed for fireman but Georges adapted his father's design for use under water. What stopped Georges from further development was his death in a allied tank in 1944.

 

After the war during a press interview about his Aqua Lung a reporter asked Cousteau about Georges Commeinhes much earlier patents,  Cousteau implied that Georges' death was due to his regulator being inferior and that it had killed him which was far from the truth.

 

https://divescrap.com/DiveScrap_INDEX/Commeinhes.html

 

http://cg-45.com/regulators/Commeinhes/index.shtml

 

Usable Rebreathers existed in the 1800s

 

Demand regulators were also in use in the 1800s.

 

Timeline of diving technology

 

 

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nice SD!  ihad no idea.

 

speaking of rebreathers, there’ve been some prototypes brought to my old department.  we went with higher pressure scbas instead.

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6 hours ago, Alpo said:

NDSTC, Panama City. '89 to, I think '97 was the last year I did an inspection there.

 

Now this is pathetic. I have been searching the entire dang internet, looking for a picture of the FAT Tower. This is the only one I could find. You can see the pretty blue swimming pool. And I circled the tower, because if I didn't know where it was I probably would have missed it.

 

21_big~3.jpg

 

 

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