High pressure vs low pressure tanks

[Rusty Nail]

I'm considering buying my own tanks and would like to know what tank would let me get the safest, fullest fill. Being new to the sport I still have some minor issues with running out of air faster than others. On average, about 25 minutes @ 80 feet is max for me. According to my Vyper Air computer graph, I burn most of my air during my decent and the first 5 minutes I'm on the bottom (over 200 lbs every 2 minutes.) and then I settle down.
So my question is: Is there a tank that I can fill to around 4000 psi to get more bottom time?

 

[ScubaSteve]

I'm considering buying my own tanks and would like to know what tank would let me get the safest, fullest fill. Being new to the sport I still have some minor issues with running out of air faster than others. On average, about 25 minutes @ 80 feet is max for me. According to my Vyper Air computer graph, I burn most of my air during my decent and the first 5 minutes I'm on the bottom (over 200 lbs every 2 minutes.) and then I settle down.
So my question is: Is there a tank that I can fill to around 4000 psi to get more bottom time?

There are high pressure thanks out there that can go as high (I believe) as ~5000psi. The BIG question is, will anybody be able to fill them to that level. I too went through air like a hoover when I first started diving. My decision was to buy HP Steel 120's and that sort of leveled me out with most people. After I got some experience, my SAC got better and my dives lasted longer. I am now not too far off where my buddies are at for SAC, thus allowing our dives to even out almost. BUT, my 120 is great when I get a full fill. Not everybody gets it to 3442.....3000 is common depending on where it is filled.

My recommendation is to worry less about your air consumption and focus more on enjoying your dive. Comfort and experience (I am factoring trim and rig set-up in experience) are what will drop your SAC, thus extending your dives. See if you can try out different tank options while diving. My 120 is a bit longer which helps trim me out nicely. This might not be the case with a shorter person. Steel also has favourable weighting characteristics for me (i.e. not buoyant when empty like AL80's and they are heavy thus eliminating weight from belts and pockets). Bottom line is, try to find the tank that works best for your diving (air volume, weighting, trim etc.). I might look into trying some LP108's in the future to see if I like them. They will be easier to fill full consistently because they are LP......but I will only get them if they have the "+" rating, thus allowing the +10%.

 

[Jim Lapenta]

I perfer LP tanks. Less expensive, easier to get a good fill, and often easy to get a real good fill! ALso known as a cave or wreck fill.

But the first thing you need to do from the sounds of it to get better air consumption is to RELAX on your descents, and do a proper weight check! It sounds like you may be struggling to get down and get comfortable. That is often a training issue for new divers who have not been taught proper weighting, rushed through training, have not had enough instruction in proper buoyancy and trim, and are put in open water too soon.

A different tank is not going to help in those areas. It's a gear band aid to a skills problem and doesn't really address the issue.

As far as tanks do go though if you really do think you need more air you need to figure out how much more and go from there. Pressure is not as important as size. You need to figure out your SAC rate. Resting, working, and average them. Decide if you want aluminum or steel and then find out what kind of fills you can get. As Steve noted not all shops can or will fill a HP tank to it's rated pressure.

LP's you don't have that issue. Most everyone can fill to 3000 PSI and will do so. I like LP 85's, LP 72's, and LP 95's. I have all of them, and just picked up a pair of lp 75.5's for my sidemount rig. These are all rated a 2400 psi with a plus rating of 2640.

Taking the LP 85's if I get them filled to the normal fill of 2800 that can get easily here they are now 90 cu ft tanks. If I fill them myself to 3200 for a wreck dive in the Great Lakes I now have 103's.

Something like a HP 100 is only that if I get a 3442 fill. At 3000 it is only 87 cu ft. And it was more expensive. If the shop gave it a hot fill and it cools on the way to the dive down to 2800 or so it's now only 81 cu ft. Whereas if a hot fill of 3000 in the LP 85 cools to 2800 I still have a 90 cu ft tank.

I suggest reading this article before you buy tanks - NWGratefulDiver.com

It's by SB member NW Gratefuldiver and is one of the best articles I have read on the subject. I use it in teaching my OW classes.

 

[elmer fudd]

Your best bet is probably to get a pair of HP 119's or 130's. These will give you considerably more air than an AL80 and they aren't that big of tanks. As ScubaSteve mentioned, your air consumption will also drop with experience and if you keep diving actively, 6 months from now you'll likely find you use much less air.

As to big fills, these are mostly a matter of which shop you get them at, how much they are willing to bend the rules and how much they are willing to bend the rules for you. I would recommend HP tanks because assuming the shop has a decent compressor you can at least expect to get your tanks filled to a minimum of something like 3200.

 

[Tortuga68]

The BIG question is, will anybody be able to fill them to that level

Right. Without a filling station an HP tank is just an expensive, heavy LP tank

 

[Superlyte27]

Where will you be diving?
There's a certain region of Florida where every fill is a 4000psi fill. I prefer to get these fills in LP tanks.

 

[uncfnp]

I'm considering buying my own tanks and would like to know what tank would let me get the safest, fullest fill. Being new to the sport I still have some minor issues with running out of air faster than others. On average, about 25 minutes @ 80 feet is max for me. According to my Vyper Air computer graph, I burn most of my air during my decent and the first 5 minutes I'm on the bottom (over 200 lbs every 2 minutes.) and then I settle down.
So my question is: Is there a tank that I can fill to around 4000 psi to get more bottom time?

Before I bought my HP 80's I checked with each dive shop that I would most commonly be using for fills. All assured me HP tanks were no problem and so far thats been true. I usually have 3500 to 3600 when I pick them up (South Florida). I'll also add that after talking with the shop I use most, I had them O2 cleaned. If I had not checked with them prior to my first trip, I would not have known I needed this for fills at this shop.

So if your reasonably sure of good fills, go with an HP 100 or 120. Reasonably sized tank and plenty of air.

 

[Rusty Nail]

I have mostly been diving in Ft. Lauderdale and Panama City Beach.
Jim, I can't say anything about my instructor (he may be on this forum) but your right about one thing, i may have been rushed through my training a bit too fast. As far as weight issues go, I am doing better on that.
In February I wore a 5 mil suit and had to put 22 lbs to get to bottom. The next trip in early March with the same suit I only needed 18 lbs. So far this summer with nothing but a scuff shirt under bc, I have went from 12 lbs to 8 lbs.

 

[elmer fudd]

Right. Without a filling station an HP tank is just an expensive, heavy LP tank

I tend to look at it the opposite way. An LP tank tends to be big, heavy and 2/3's full. Compared by approved capacity, LP120 vs an HP119 for example, the LP120 is 10 lbs heavier and 5 inches longer. Even when you compare tanks with similar dimensions, LP80 vs HP100 for example, the weights are nearly identical.

I don't know any shop around here that can't fill to 3600, but most will not do overfills unless they know you.

 

[chrpai]

I'm considering buying my own tanks and would like to know what tank would let me get the safest, fullest fill.
...
So my question is: Is there a tank that I can fill to around 4000 psi to get more bottom time?

Any properly inspected and properly filled tank will be "safe". Some tanks are known for being even more then properly filled and are debatably still safe. So let's ignore the "safety" concerns.

You asked "fill to around 4000". This indicates that you are looking at it all wrong. I could show you one tank that's filled to 4000psi and only has 8 cubic feet of air in it. And I could should you another tank that's only filled to 2400psi and yet has 86 CF of gas. That aluminum 80 that you dive at 3000 psi really only has 77.5 cubic feet of gas. If you get a hot fill (filled fast to 3000psi then cooled to 2700psi ) it really only has 70 cubic feet of gas. That tank with 86 CF of gas and only 2400 psi actually has 20%+ more then that hot filled tank. Properly filled to 2640 PSI it has 95 cublic feet of gas which is nearly 40% more. Cave fill that tank to 4000psi and your talking about 140+CF of gas. That's like 2 of those hot filled 80s.

But that's only part of the equation. Another big factor in choosing a tank is your weighting. How much and where you need it for trim.

It's really a long conversation. You should find a buddy / mentor to help you understand all of this, make sure you are perfectly weighted and trimmed and start working on relaxing to get your air consumption rate down. Then learn how to plan your gas needs for a dive so that you know how big is big enough. Finally select a tank that meets your weighting and trim needs and you'll end up with the perfect tank for you.

For some, the AL80 is the perfect tank. For others it's merely commonly available.