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Modern Subs also pressurize to maintain 1BAR, but how do they do it? Do they take air out of the Fuselage to maintain pressure, then add it again as they ascend? It seems to me that no matter the volume of air in the fuselage, it should still compress?
thus with every breath you are taking in extra nitrogen in accordance
with how many BAR you have descended.
It seems to me that no matter the volume of air in the fuselage,
it should still compress?
For example, how is a sub half full of air any different then if
I blew out half the air in my tank on a dive?
lots of plans for doing so on the Internet. All the ones I have found so far,
work in a similar manner to regular scuba gear
Originally posted by LordBucket
I think you may be making this more complicated than it needs to be. The only reason SCUBA gear needs to deliver pressurized air to you is to keep your lungs from collapsing due to water pressure. If you simply build the hull of your submarine sturdy enough to withstand the pressure, you should be able to forego any need to pressurize the cabin, as well eliminate as any need to slowly surface to give your body time to eliminate the nitrogen.
Originally posted by LordBucket
Yes, but the nitrogen is just to prevent oxygen poisoning from breathing pressurized air. If you don't pressurize the air, there's no need to add nitrogen.
Originally posted by LordBucket
...one of the two of us doesn't understand your question. The volume of air in the cabin will remain constant, whether or not it is "pressurized."
Originally posted by LordBucket
Air pressure in a submarine at the bottom of the ocean is the same as the air pressure in a submarine sitting on the surface. The cabin is not artifically pressurized. They simply build the hull out of a solid piece of metal that can withstand the greater water pressure around it. Whatever air pressure is on the surface, they simply close the hatch and submerge, maintaining that same internal air pressure at all depths.
Originally posted by LordBucket
...again, one of the two of us doesn't understand your question. How can a sub be "half full of air?" As to your divetank, when you "blow out half the air" the air pressure in your tank will be half, even though the "volume" of the tank remains the same.
Originally posted by LordBucket
There may be some confusion here simply because US dive shops tend to use cubic feet to describe air pressure, which is somewhat misleading.
Originally posted by LordBucket
...if the plans you're working from involve a pressurized cabin...then what I've said above would not apply...but if so, I would expect them to also include the information you need. If they don't, well...you might consider not using those plans.
Originally posted by weedwhacker
Quite an undertaking you're trying to accomplish, there!
Originally posted by weedwhacker
Coming from a layman's view (I'm only a sport diver, no NITROX!!) I believe that UP TO a certain depth, depending on the structure of the vessel, a regular 14.7PSI N/O2 blend can provide a normal 'shirt-sleeve' environment...but I suppose that assumes a self-contained air supply.
Originally posted by weedwhacker
From an opposite standpoint, the early Space Program decided on a 100% O2 approach,
Originally posted by weedwhacker
a rigid vessel should not convey the exterior pressure.
At 33 feet that 80cf at surface pressure is now 40cf
The only reason SCUBA gear needs to deliver pressurized air to you is to keep your lungs from collapsing due to water pressure.
See that is the bit that gets me. My SCUBA tank is a rigid vessel, yet my air decreases in volume according to the pressure that I am under. As you know, you only get ½ PSI at 33 feet, 1/3 at 66, ¼ at 99… etc… Yet as my tank is basically a rigid cylinder, same as a sub, why does it not get effected the same way?
Originally posted by defcon5
reply to post by Phage
At 33 feet that 80cf at surface pressure is now 40cf
Then shouldn’t the PSI drop by half accordingly?
So are you saying that the PSI is not changing, it’s the expansion or compression of the air as it goes through the first stage reg yet it remains constant in the tank? Increased flow maybe?
Originally posted by Phage
No, I worded that badly (probably should have left it out entirely). If you fill a balloon from an aluminum tank at sea level it would fill a volume of 80cf. If you did the same 33ft below the surface it would fill a volume of 40cf because it is under twice the pressure. In the balloon, the internal pressure equalizes with the external (the skin of the balloon will cause a bit more internal pressure).
Originally posted by Phage
One more (I hope this doesn't confuse things more); if you have an empty (a vacuum) submarine which had a volume of 80cf, take it to any depth and release the tank into it, the internal pressure will be 1atm.