PDA

View Full Version : why dont we have 4500psi tanks?



sid101
05-27-2008, 06:52
i dont know if you guys know but there are sport 4500psi tanks out there as an example:

Crossfire Nitrogen Systems at ActionVillage.com : Paintball (http://www.actionvillage.com/is-bin/INTERSHOP.enfinity/eCS/Store/en/-/USD/BrowseCatalog-Start;sid=s60T3LlT89oTwfFoS-vTdLOaOhzwFI3TiZ8=?CategoryName=paintball-gas-systems-nitrogen-systems-crossfire-nitrogen-systems)

for whoever of you who know paintball already know this but for who doesnt well may i introduce you to this special kind of tanks, they are not steel or pure aluminum they are one layer of aluminun and a layer of carbon fiber to make them lighter, these tanks are made to take lots and lots of abuse (i know this because i used to play paintball) so... why is it so hard/impossible for scuba tank manufacturers to make some scuba tanks at 4500 psi? i think it would be wonderfull... specially for tech divers and semi-close rebreather users, i know they are quite expensive but believe they are light, tough and as i know they are expensive because fo their greater pressure you could use a smaller tank and get the same amount of air (i knwo my back would be thankfull because i have a interdiscal herniation wich makes carrying a tank in my back paintfull sometimes specially after a dive), the biggest paintball tank out there is 72 cubic inches(i think theres a 80 or 85 ci tanks out there but im not sure) i dont knwo if theres some kind of pony botle that small...


ah this tanks dont have positive buoyancy btw...

and besides...

http://i18.photobucket.com/albums/b109/CristianSanchez/tankeexplivo.jpg

this doesnt hapen to those tanks... paintball tanks of 4500psi are tested to up to 7000 psi and if you ever manage to make one break this is what happens:
(in this image you can also see the two layers of material these tanks are made from)
(they can also be hidro tested)

http://i18.photobucket.com/albums/b109/CristianSanchez/burstbottle1.jpg

P.D: excuse my english im nto form an english speaking country so i made soem mistakes every once in a while.

Rainer
05-27-2008, 07:10
What makes you think divers want light (read: extremely positively buoyant) cylinders? Yeah, I get to wear 20+ extra pounds on a weight belt. And get to pay even MORE money that for HP steels. And they have an expiration date, no? Lame.

comet24
05-27-2008, 07:26
A scuba tank needs to have enough weight to make it at least neutrally buoyant when full. I don't want a tank that starts out positive and have to wear weight to get the tank under.

mitsuguy
05-27-2008, 07:42
agreed, this has been hashed out before...

common consensus always ends up being that price vs performance, an HP steel is the best buy for a scuba cylinder...

The 80CF HP Steel tanks I've been using lately (rented from LDS), are 1 lb lighter than a 80CF AL tank out of the water, hold 1.5 CF more air, but are 4-5 lbs more negative in the water... oh, and they are about 8 inches shorter I believe as well... best of all worlds - more air, less weight dry, more weight wet, and a smaller form factor...

ianr33
05-27-2008, 07:58
I dont think these tanks can be re-hydroed. Use for 5 years then throw it away.

Geoff_T
05-27-2008, 08:34
not to mention the increced volume presents some other problems. If you drop a small paintball tank it will probially be ok. If you drop a large scuba tank that relys on the carbon fiber for integraty you could have some problems. I have personaly had two professional grade carbon fiber tripods that had to have legs replaced due to splintering. Then there is the fact that these tanks are constantly submerged and taken out of cold water close to 30 degrees in some cases. I would strongly suspect that this heating and cooling would cause gaps to form between materials eventually leading to the pictures above.

ReefHound
05-27-2008, 08:44
Perhaps a steel/carbon fiber tank could solve the weight issue. But you would still have a problem with getting air fills. Many shops/boats can only pump to 3000 to 3500 psi. Pressure costs money so those who can fill them would probably charge more.

doczerothree
05-27-2008, 09:21
It's a pressure and shape thing. rounder type cylinders can handle greater pressures because round (or a similar configuration) is stronger. diver need and want more volumn. scuba tanks are round but also long(er). sure there are tanks that can manage more than 6000+ psi but because of thier shape I'm not sure I would dive with one. remember "streamline" "drag" application and comfort

fisheater
05-27-2008, 09:24
Of course, your reg would probably protest a bit at those pressures.

cummings66
05-27-2008, 11:24
There are SCBA cylinders out there that do those pressues, and they do have finite lifespans plus it doesn't take much damage to condemn them. Damage I should mention that I'm sure a diver would inflict on them.

Luxfer makes a cylinder like the OP wants, but I've never seen one in captivity. It's buoyancy characteristics are very similar to an AL80 in fact. I've posted here many times about it when people say it'd be way to light, there is no such thing, etc. There is, it's not that light, and Luxfer makes it. Nobody I've ever talked to has seen one, that should tell you something about it.

sid101
05-27-2008, 11:55
Woah, i feel like im getting flamed in here.

Sorry guys i forgot to put some stuff on the original post..

This tanks are light but they dont have positive buoyancy i have tested my old paintball tank with 4500 psi under water and its a litle bit negative.

The tanks as you see are expensive but part of the price you see is because these tanks come with a preset output valve with them that valve alone is 120$+.

these tank can be hidroed i knwo this for a fact because i have seen it myself in the US.

as far as splintering or gapping due to temp changes i dont think so since these tanks are used very fast they can lose all of the pressure in less than 10 minutes just by shooting and the recharge time is less than 2 minutes they get a litle hot while filling and then shooking a litle cold, believe me this tanks ar emade to last a lot and take a serious pounding.

I agree i cannto say this si the way to go just because they use a lot of pressure and if so a lot of test have to be made but at the same time... wouldnt we all want to have a tank that is smaller and last longer?..

P.D: most store compressors for scuba tank filling actually work to 5000psi as a regular working pressure, but since cascade tanks ussually cant handle that pressure.

js1scuba
05-27-2008, 12:11
There are a few reasons why super high pressure cylinders are not readily used in scuba. I will explain.

1. Most Yoke style regulators can only take a supply pressure of up to 3500 psi. (CGA rating for yoke and o-ring extrusion)
2. 4500 psi would require DIN only connections
3. Weight -- to make steel cylinders handle 4500 psi require them to be quite thick, and for aluminum require them to not only be thicker but wrapped.
4. Most scuba store compressors cannot delivery 4500 psi fills -- this will result in most tanks being short filled.

Now ..... there is a cylinder made by Luxfer for Scuba that is a high pressure 4350 psi (300 bar) cylinder. It's called the Luxfer Limited and was first created in 2002 on a trial basis designed to compete with some larger capacity steel tanks. These are aluminum cylinders that have a kevlar wrap around them, known as a "hoop wrap". The sizes are 80 cuft and 106 cuft. They have the physical size of a standard 63 and 80 but larger volume due to the higher working pressure. They are 7.39" diameter due to the "wrap".

These were produced for a few years but were a bit expensive and did not take to the market place. I have about 10 of them and use them here for shop air cylinders. Luxfer will still make them on special order.

Some other downsides to these cylinders are:

1. Hydro Test every 3 years
2. Remove from Service after 15 years.

Hope this helps you.

sid101
05-27-2008, 12:32
ah ok now i understand, so its basically a good idea but the overal technology cant support it... thank you very much for clearing things for me.

js1scuba
05-27-2008, 22:22
ah ok now i understand, so its basically a good idea but the overal technology cant support it... thank you very much for clearing things for me.

The technology can support it -- what can't support it is the economy. You can get a much more viable steel cylinder for the same price as the limited used 300 bar aluminum hoop wrap.

I've had no problem filling the cylinders on my fill system, nor using din regulators -- it's just not an attractive option. One is better off with an equivalent sized steel Faber tank.

Cheers

WD8CDH
05-30-2008, 14:42
Most of the carbon fiber tanks are 5 year hydro. The fiberglass tanks are 3 year hydro. Most of the composite tanks are 15 year life but Luxfer makes a series of carbon fiber tanks that are 30 year.

At present, only the Luxfer S106W 105.2CF@4350psi tank is produced and DOT certified for under water use. None of the SCBA ("firefighter") tanks are certified for underwater use.

As far as buoyancy and weight, if you add weight to a SCUBA sized composite tank to make it the same buoyancy as a steel tank, the combined weight would be less than a steel tank of the same pressure and capacity.

In europe, you CAN buy ~4500psi composite SCUBA tanks. In fact, one of the european carbon fiber SCUBA tanks doesn't even have a metal liner, just metal valve threads.

By the way, one of the problems with composite SCUBA tanks is a galvonic corrosion between the carbon fiber and the aluminum liner if there was a defect allowing water to get to the liner. It's difficult but not impossible to get around that problem.

I think 7000 series aluminum alloy is a better and more cost effective solution for 4500psi SCUBA tanks.

longtailbda
05-31-2008, 05:37
With todays materials, ect., it is possible to create a higher pressure tank system that can be re-hydroed. The problem is the current infrastructure is set up for existing pressures.