3000psi tanks...why?

[Token]

Is there a reason that a standard tank fill is 3000psi? Most air gauges go to 5000, and obviously, more air means more bottom time.

The reason I ask: On a recent dive, I was by far the biggest person on the boat. I weigh about 220lb, and everybody else was well under 200, including two women that probably weighed not much more than half what I do. As you might expect, I started to run low on air before everybody else, although I did make it through a 45 min dive with a decent safety margin. Would it not make sense to give the biggest guy/people on a dive party a tank with more air to forestall an early end to the dive? Would it be reasonable for me to request a 3500-4000psi tank to increase my bottom time, or is 3000psi an established safety practice?

 

[fjpatrum]

I believe 3000 psi is fairly standard, as is 2400??? for some of the big steel tanks, I think. There are people who will "overfill" your own tanks to 110% or something like that but I doubt you'll find any rentals where you'll get those kind of fills. If you're big and a gas hog, your best bet is to try and find a larger tank, rather than one with a higher pressure fill.

 

[mathauck0814]

The reason that SPG read to 5000 is because they are less accurate at either end of their spectrum. Because you're supposed to end up back on the boat with ~1/3 of your gas left (in the case of a 3000psi tank, that's 1000psi) you shouldn't ever be at the high or the low end - which gives you the highest degree of accuracy.

The ratings on tanks is a safety measure. You CAN overfill some tanks, but not without consciously accepting what you're doing. A steel tank can be "officially" overfilled if it is hydro inspected with a "+" on the stamp. This means it has been inspected and deemed to be safe to fill to 110% of the marked service pressure. Anything higher than that (or overfilling a tank that's not marked as such) is a risk that you are taking and one that the fill station operator must agree to - afterall, if the tank blows up and you're not there, guess who bares the brunt of that mistake?

Aluminum tanks should never be overfilled as it can cause the tank to become brittle and cause a tank failure/explosion. Which is un-good.

 

[Ulfhedinn]

I dont know if purchasing a tank is an option but I got a steel 130. I have never looked back. Lots of air. Drop 6 lbs from diving Al80

 

[DandyDon]

Welcome to Advance Scuba discussions.

Ask for larger tanks.

 

[TSandM]

Tanks are rated for how much pressure they can safely contain, based on the volume of the tank and the material of which it is made. The standard rental tank in many resort locations is an aluminum tank which, when filled to rated pressure, holds 77 cubic feet of gas (why it's called the Al80 is beyond me). Aluminum is not a metal forgiving of overfilling, so aluminum tanks are generally filled only to the rated pressure.

Steel tanks, on the other hand, come in a variety of rated pressures, from 2200 to 3400 psi. As you can imagine, for the same physical size tank, the higher rated pressures have higher volumes. They are also considerably more expensive, and thus they are rarely found in rental fleets.

So the answer is that you can't ask the dive operator to fill your tank to a higher pressure than your buddy's tank is, because they can only fill it to the rated pressure of the tank. To get more gas, you have to get a different (physically larger, or higher rated pressure) tank.

 

[g1138]

You want to ask for a higher capacity, larger volume tank. PSI alone doesn't tell you how much air you have, it tells you how much air pressure you have. You need to know the volume capacity of your tank to know how psi factors into how much air you have.
Ask for an HP 120 tank if you want more air. You'll probably have to recheck your weight though if you're trying out new tanks you've never dove with before.

As for why 2400 and 3000psi are the standards, I do no know.

 

[ajduplessis]

I am generalizing here but in Europe and here in South Africa all ALI cylinders are 3000psi (200 bar) All steel start at 3500 (232bar) and some are even over 4000psi (300bar). ALI here are primarily used for stages/deco bottles.

Fill stations will give you 3200psi as standard. Anything less and you where "robbed".

Buy steel! Its a better backgas bottle and will last a lifetime if cared for.

My steel doubles give me 247cubic feet of capacity. Life is awesome!!!!

 

[Keith & Sharon]

Since diet and exercise was not an acceptable short term solution by lowering my sac rate (long term solution), I purchased steel tanks to solve this problem. LP 108's normal fill at +10% is 2640psi. Many tech dive shops will fill to 3000psi if you request, which will provide approximately 125 cuft of gas. Now if you burn 125 cuft by the time others burn 80 cuft, then work on long term solution a little sooner.

On vacation dives where you are renting tanks, ask if they have AL 100 or a steel tank to rent. One other suggestion is to stay 10 to 15 feet above the group (with buddy). Additionally, the less you are kicking and swimming, the better your rate of consumption. Every exhale get 6 seconds. Good luck and safe diving.

 

[Dive-aholic]

Compressors work more efficiently and last longer when run to lower pressures. The cfm ratings for most compressors is in a range less than 3000 psi. Above that and your cfm decreases. Most resort ops will not fill beyond 3000 psi even if they had the cylinders because they need their compressors to run efficiently and to run! While many of us will run a compressor to higher pressures it does mean more maintenance will be required.