Need help determining what tank would be best for my diving.

[DavidHickey]

I'm getting ready to purchase a new tank, and need a little advice. I use alot more air than my Fiancee, she generally surfaces with close to 1500 psi while I'm at 500 to 600. My LDS tells me not to worry about it that I'll get better with experience. BUT if it works that way then SHE will also get better. Its been sugested that I cut her down to a 63 cf tank. But that seems silly to me. I figure that being twice her size I should easily be able to handle a bigger tank with less strain than it is for her to carry the 80 cf tank she currently has. Anyhow doing some research I THOUGHT that my best option would be a steel 119 cf high pressure tank. Being as its not a whole lot bigger and heavier than a regular tank. BUT it seems that everyone I talk to tries to talk me out of it. The last dive shop owner I spoke with yesterday said he did not understand the whole mentality behind the high pressure tanks. He said that they are more expensive, almost nobody in the area has the ability to fill them to capacity. But of course he had 2 steel low pressure 95 cf tanks in stock he was trying to sell me. But what is confusing me is the standard aluminum 80 cf tanks are rated to 3000 psi. The low pressure steel 95 tanks he has are rated to 2400 psi, and the High pressure 119 cf tank is rated to 3442 psi. From what he said most places will fill the lp 2400 psi rated tanks to 3000. And most will only fill the high pressure tank to 3000 and from his math I'm better off with the low pressure. I'm just having a hard time with all the different sizes and pressure ratings figuring out which tank will actually help me more without throwing my weighting and bouancy way off. I'd appreciate any advice anyone may have on what tank might work best for my needs to give me a little extra bottom time to even myself and my fiancees air consumption out. If it helps my main diving will consist of Local Ohio quarries were I'll be wearing 7mm wetsuit in spring and fall and 3mm in mid summer. I plan on other trips to the ocean but of course will not be shipping tanks. Oh, I was quoted 225.00 for the low pressure 95's and around 350.00 for HP 119's
Thanks
David Hickey

 

[m3830431]

Do a search an tanks and you will get every opinion possible. It depends on how you are going to dive.

If you dive only an Al 80 now and your buddies are diving the same the smart play would be a steel HP 100 even at 3000 psi you get 89 cf O2 compaired to 77 cf with the 80.

Additionlay the steel remains negatively bouyant so you loose lead.

The LP tanks are larger in size and weight more. The ones that are over rated are usually only 10% which will give you 104 cf in a 95.

 

[diverio]

Download this pdf file; http://www.pstscuba.com/specsheet.pdf

Consider this;
Take your E8-100 and fill it to it working pressure 3442 and you have 100 c.f.
Take the same tank fil it to 3000 psi, if you're dive operator isn't willing to fill it to its WP. You're still going to have a bit more air than if you were wearing an 80 c.f. tank at 3000 psi. If you're dive operator is good enough to fill it to its WP then it's not an issue. These tanks are at least twice as much as a standard alum. 80. The other aspect is that you'll be able to take some weight of the weight belt because of the heavier/less buoyant characteristics of the steel tanks. The PST tanks are backordered till next spring but I know there are sometimes dive shops that have some in stock.

Nelson

 

[PerroneFord]

If you're trying to keep your breathing on par with your fiancee, you're fighting a losing battle. Going to a big tank is certainly one way to close the gap a bit, but it's not without it's drawbacks.

For many people, the single steel tank is a good thing. It holds more gas, it's less buoyant so you get to remove some lead from your weightbelt, it doesn't weigh much more than a common aluminum tank, so it's not so unweildy on the surface. For most people these are all positives.

Then comes the issue of high pressure versus low pressure. High pressure tanks tend to me rather small in size until you get to ones of quite large capacity. The drawback to them is that many places can't fill them to their rated capacity (especially in remote areas) so your expensive HP tank just became the equivalent of a small 80 or less depending on the size you purchased. Also, some of the smaller ones make getting in proper trim harder because they are quite short.

Low pressure steel tanks tend to be closer in size to the aluminum 80 unless you go to the very large sizes. However, they are easy to get filled, and usually overfilled. The offical overfill is 10% which means their 2400 psi becomes 2640. It is not uncommon for these to filled beyond this, but I won't advocate that. The low pressure steel tank will let you fill to it's capacity almost anywhere because it doesn't require overfilling to get a decent amount of gas in it. They are also quite a bit cheaper as you found out.

How often are you diving? It might be that you will get much better with your breathing in the water. You were right that your fiancee might also do that, but to be honest, if both of you are able to stay in the water for an hour or more on a single Al80 tank, is that enough? At some point, the limiting factor will become the boat's schedule, or the fact that you are getting cold, or the fact that others in your group will be short on air, etc. Perhaps you are overweight in the water (very common) and you are trying to swim around too much lead. How is your trim in the water? If you are overweight, you are not able to be horizontal in the water and it takes a LOT more effort to swim around in a fin-down position. That alone could put 500 psi back in your tank over a 45 minute dive.

I understand that getting a bigger tank is an expedient solution to your problem, but it might be useful to look for the cause before you go buying a solution.

Best of luck to you.

 

[rab]

The LP tanks are larger in size and weight more. The ones that are over rated are usually only 10% which will give you 104 cf in a 95.

The '+' rating for 10% overfill is taken into account for an LP95. You get 95cu.ft. at 2640psi (2400+10%).

That being said, I have two PST E8-119 steel tanks. They are essentially the same dimensions as an LP95 so you get this benefit:
2400psi => 83cf
2640psi => 91cf
3000psi => 103cf
3300psi => 114cf
3442psi => 119cf
Do I wish that I'd get a full 3400+ psi fill? Yeah! But recently I did 5 dives on three fills because even starting with only 2900psi (that's right, short even for an AL80!) I surfaced from a 40-45min 1st dive with 1500-2000psi and could do another shallow dive for 30-40min. Of course, I'm coming up from that 2nd dive with 500psi (or less), but these are quarry dives (one was a night dive, too).

Did I mention that I need no extra weight in fresh water with my 5/3mm full wetsuit and only 10# with my 7mmFJ/J? It took quite a few dives to get that weight dialed-in properly (partly because it was hard to get the tank empty enough to do a proper check!), but it's still very nice to have the weight on my back rather than my pockets.

I'd absolutely tell you to seriously consider the higher capacity tank. Don't make a decision based on what pressure somebody says you can (over)fill an LP tank. Go with a combination of rated pressure and, more importantly, expected fill pressure.

Look at the example you gave for your and your wife's air usage:
You: (3000-500)/3000 * 77.4cf => 64.5cf
Her: (3000-1500)/3000 * 77.4cf => 38.7cf

You use air 64.5/38.7 => 1.67 times as much as she. So, if she uses a "whole" AL80 (that'd be 64.5cf, just what you're able to use), then you'd need 64.5*1.67 => 107.5cf to "keep up" (i.e., not have to call the dive first). Since you still need to have a reserve, let's say 500psi to keep it consistent (even though the same reserve volume will be less pressure in a larger tank). With an E8-119 to rated pressure, you have (3442-500)/3442 * 119 => 101.7cf of "usable" air (gas). OK, so you still might have to call the dive before she does, but it will be a longer dive. (And if she gets cold first...)

-Rob

The results for an E8-130 are left to the reader.

 

[PerroneFord]

You should take rab's comments very seriously. It's excellent. However, there are a few things I wanted to point out.

rab is correct in that the 10% overfill is taken into account in the LP tank's capacity. It is also true that at some point that "plus" rating may be revoked and you will be left with a tank that can only be filled to 2400psi legally. High Pressure tanks do not have this limitation.

rab also mentions that he needs no extra weight in fresh water. While this may be true, I would not advocate diving a system as a new diver that had no ditchable weight. In fact, I wouldn't advocate it for anyone, but if someone with 500 dives decides they are comfortable not having any, that's their business.

I also agree that a decision should be made on what tank to purchase based on both expected fill pressure and working tank pressure. However as a newish diver, you may not have a firm grasp on what you can get your tank filled to each time. Generally it's safe to assume you can get a 3000psi fill in most places.

If rab's numbers are correct (and I think they are), you are using gas 1.67 times faster than your buddy. That gap will close on it's own though it may not do it for some time, and it will probably never close fully. What rab's post fails to address is that it is entirely possible that you don't need a new tank at all. But rather you need to improve your ability as a diver. There are many large men who easily get over an hour out of an AL80 at recreational depths. If you purchase your large(r) tank, and become a better diver, and you overtake your fiancee's consumption, will she then get a larger tank to keep up with you? At what point do you say you both have adequate amounts of gas? 45 minutes worth? An hour? Two hours? I think this should be the primary factor in determining the tank on your back. The $100 difference between the low pressure and the high pressure will be forgotten down the road. The few pounds of buoyancy one way or the other wont' make a lot of difference. It's really not that huge a decision in the grand scheme.

Again, I wish you all the best.

The '+' rating for 10% overfill is taken into account for an LP95. You get 95cu.ft. at 2640psi (2400+10%).

Did I mention that I need no extra weight in fresh water with my 5/3mm full wetsuit and only 10# with my 7mmFJ/J? It took quite a few dives to get that weight dialed-in properly (partly because it was hard to get the tank empty enough to do a proper check!), but it's still very nice to have the weight on my back rather than my pockets.

I'd absolutely tell you to seriously consider the higher capacity tank. Don't make a decision based on what pressure somebody says you can (over)fill an LP tank. Go with a combination of rated pressure and, more importantly, expected fill pressure.


You use air 64.5/38.7 => 1.67 times as much as she.

 

[pants!]

LP95's are nice, especially when pumped up a bit.

HP100s and E7-100s are better.

 

[RonFrank]

Hi David,

First off, you have not bothered to fill in any dive profile, so it's difficult to determine how much diving you have done. BUT, you SAC rate will improve if you keep diving.

Keep in mind that it does not matter what anyone else surfaces with, the key is more, can you get through the dive plan that you intend on the air you have. If you are not able to stay down for say 30 minutes at 50', they maybe a larger tank is a good idea.

On my OW dives I was about the worst air hog in the bunch. After about 40 dives my SAC rate is as good or better than most people I've dove with including so Locals at LBTS where they often exceed 90 minutes on a dive (which we did).

IMO if you are thinking that you MUST have a larger tank, start out with an AL100. The AL100 is not all that much bigger than the AL80. The buoyancy charasteristics are not as good, but the price is MUCH less especially if you can find a couple used.

Another thing to keep in mind is that improving SAC rates is a valid goal and when you go on vacation, you will be diving AL80's at most places, or paying a heavy premium for larger tanks IF you can even find them.

There has been some good posts on SAC rates, and Scubadiving magazine had a real good article a while back on things one can do to improve breathing.

If you are positive you want to go big, and steel, IMO budget for two. I'm not sure where you are diving locally, but one tank = one dive, and if you are going to drive somewhere to dive, unless you can get a nearby fill, one tank is not enough.

Good Luck,

 

[pickens_46929]

Becareful here... +10% is the normal operating rating for the tank during the first 5 years (or after you specifically have it Hydro'd with + testing)... that means... you only get 95 cu.ft. if you are at 2640 psi...

Still not bad plus it's easy to get a 2640 psi fill pretty much anywhere. I do ocassionally overfill my LP 85's to 2900 or 3000 which does get me 94 cu. ft. in my LP 85's.

Do a search an tanks and you will get every opinion possible. It depends on how you are going to dive.

If you dive only an Al 80 now and your buddies are diving the same the smart play would be a steel HP 100 even at 3000 psi you get 89 cf O2 compaired to 77 cf with the 80.

Additionlay the steel remains negatively bouyant so you loose lead.

The LP tanks are larger in size and weight more. The ones that are over rated are usually only 10% which will give you 104 cf in a 95.

 

[pants!]

I disagree with the suggestion for an Al100. They weigh more than LP95s or HP100s or E7-100s and require you to wear more lead than any of the above tanks. They are also quite a bit larger than any of the above tanks.

Bad, bad choice.

Al100s? Bad.