Steel HP 100 vs AL80

[Jrock1062]

Hello All
I am looking for a little help here, can someone tell me why you would bye a AL over a HP ? Or any LP tank over a hp tank for that matter, seems to me a no brainier for the hp tanks. Thanks all for the help

 

[medic001918]

Some people get LP tanks and get a "cave fill" where they fill the tank well beyond it's listed pressure. Some people use aluminum tanks due to cost, since they're generally about half the cost of a steel tank. And an HP tank can be limiting if your shop can't fill a tank to 3500 psi (there are some that can't do this).

The nice thing about a HP tank is that you get more air in a similar size package. For example, my wife dives a steel HP100 which is very comparable in size to an AL80 while at the same time remaining negative even when empty. I generally dive a single LP108 because I like the buoyancy characteristics of it. It works well for me.

I'm in the process of setting up my first set of doubles though and I got a set of AL80s. Part of this is because I got a deal on them, but also to keep weight manageable. As I progress, I'll probably break them apart and turn them into stages and start diving backmounted steel tanks.

Shane

 

[PvtStash]

Given the same (apprx) size tanks your going to get more air with a HP tank than an LP one...

If tank size is not a concern you'll prob be able to find a (used) LP tank for a good price.

I believe I've heard that LP tanks lend themselves easier for gas mixing...

 

[spectrum]

Here my rant.

Pete

 

[Colliam7]

can someone tell me why you would bye a AL over a HP ?

Because they are relatively inexpensive compared to steel, they are the most common rental tank, and people who rent first then buy seem to most commonly transition to what they are familiar with. For backgas, single tank diving, they are OK (you will not DIE just because you use them), but they unfortunately have the buoyancy characteristics Pete describes in his rant. And, getting an AL tank bigger than 100cf is challenging, plus even the 100 is a bulky, heavy tank relative to the amount of air you get. Notably, AL80 tanks are prominently and frequently mentioned in the 'most regretted gear purchases' thread. For backgas, doubles diving you will see some animated debate about the desirability of wearing 2 AL80s vs simply diving a HP 130 or 149. I have a couple of sets of double 80s and find them to be fine for NC coastal dives. Some people have had rust problems with steel tanks and prefer AL as a result, but that experience is relatively less common than frustrations with AL buoyancy. For (smaller) pony, stage and deco bottles, AL is the strong preference, in part because of the same buoyancy characteristics that diminish their appeal for backgas use, and because of the range of sizes avaialble.

Or any LP tank over a hp tank for that matter

As noted, getting a 3442 or 3500psi fill may not be possible in some shops, whereas getting a LP 2400 filled to 3000 may be possible, irresepective of whether it is recommendable. Most people prefer a HP simply because of the favorable weight / capacity ratio (at least for rated capacity) compared to LP.

 

[DA Aquamaster]

The 3442 psi 100 cu ft tank is nearly identical in weight to the AL80, is the same diameter, is about 4 inches shorter and is about -1.7 lbs bouyant when empty compared to +4 for the AL 80, so you can usually take about 6 lbs off your weight belt with the 100 cu ft tank and consequently be carrying about 6 lbs less weight up the ladder at the end of the dive.

Lp tanks are not a good chocie in my opinion. The cave fill argument does not really apply as while you can get a cave fill in the 3500 psi range in north Florida with an LP 95 or LP 104, you do not really gain anything as with a high pressure tank of similar physical size and similar weight to the LP 95, 104 and 108 you get the same volume at the same pressure. So in effect you can buy an LP tank that holds a lot less with a legal fill or you could get a 3442 psi tank of the same size and weight that legally holds the same volume of gas at its rated pressure that the overfilled LP tank will hold with the cave fill of 3500 psi.

So except for the psychology, it is a no brainer. The psychology of it is that if a diver's A's 2640 psi tank gets filled to "only" 3000 psi, diver A is happy with the overfill. Diver A would be happier with an overfiill to 3400-3500 psi, but they are still happy as the tank is over filled. In contrast, if diver B brings in their 3442 psi tank and only gets 3000 psi Diver B is annoyed as their tank is underfilled and the fact that their 3442 psi tank is the same physical size and weight and holds almost exactly the same voluime of gas at the same 3000 psi as diver A's tank is a subtlew but important point that is missed.

What is also missed is that when diver A and diver B go to another shop thatwill not do overfills, diver B will still get a full tank (or at least more gas) than diver A who will only get 2640 psi, if the tank is still plus rated, and 2400 psi if it is not.

So in short if you want the same gas a capacity in a low pressure tank you either have to be in anarea where they will reliably pump your tanks to 3500 psi (north florida) or you need to get a tank that is physically much larger and heavier.

AL 80's offer the advantage of being inexpensive, although the difference is not that great. An AL 80 for exampel will sell in the $180-$200 range while steel tanks in the 80 to 100 cu ft range are currently selling in the $250 to $350 range. So for $50 to $100 more you could get a steel tank. Resale values are also telling as a steel tank will sell sell for perhaps 80-85% of it's new purchase price, while an AL 80 will sell for perhaps 30-40% per cent of its purchase price so in the end, if you sell the tank later, you are money ahead with the steel tank. The end result is that the AL80 is only a bargin if you buy one used for $50 to $80.

The AL100 is in my opinion a waste of money. They are more expensive than an AL 80 further reducing the cost difference compared to a steel 100, weigh a lot more than a 100 or 120 cu ft steel tank and are very large in both diameter and lenght.

 

[jpsexton]

I agree that steel tanks offer much better buoyancy characteristics than the AL80. The fact of the matter is though most places you travel to will provide you with an AL80. If you are only diving local or are in a place where you normally bring your own tank for charter trips then a steel is probably a better choice. If you travel allot and do a significant amount of charter boat diving then the AL80 is a better choice. I like the fact that whether I am diving at home in the quarry or somewhere in the Caribbean I'm still diving the same setup. The buoyancy characteristics are always the same.

 

[Adobo]

Hello All
I am looking for a little help here, can someone tell me why you would bye a AL over a HP ? Or any LP tank over a hp tank for that matter, seems to me a no brainier for the hp tanks. Thanks all for the help

In addition to what the others have said...

When one dives with doubles (or twins, depending on the continent you are on), getting yourself properly trimmed out becomes more tricky. Short tanks tanks that are very negative in the water are especially problematic. Long tanks that are not so negative allow you to balance the weight of the tanks through a larger portion of your body. In addition, you get more options as far as where to place the lead you need to weight yourself properly.

As it turns out, a few of the longer, less negative tanks are low pressure tanks. One example is the faber lp 85. This tank is right around neutral. Compare that to the worthington x7-100 which is 2.5 lbs negative and around 4 or so inches shorter. So a set of x7-100s doubled up would be about 5lbs more negative than faber lp-85s. And they would concentrate much of that weight closer to your head. Whereas you would have the ability to place that 5lbs (using lead) almost anywhere on your body to properly trim yourself out if you were diving faber tanks.

Another consideration is cost. Two examples here.. faber lp-85s cost about $50/tank less than worthington x7-100s. Worthington lp-85s cost about $75/tank less than x7-100s.

With regards to aluminum tanks.. an al-80 costs around half of what an hp-100 costs. Their buoyancy characteristics and size make them attractive to some divers (doubles in wetsuits, divers having difficulty getting trimmed out in steel tanks).

 

[Adobo]

I agree that steel tanks offer much better buoyancy characteristics than the AL80. The fact of the matter is though most places you travel to will provide you with an AL80. If you are only diving local or are in a place where you normally bring your own tank for charter trips then a steel is probably a better choice. If you travel allot and do a significant amount of charter boat diving then the AL80 is a better choice. I like the fact that whether I am diving at home in the quarry or somewhere in the Caribbean I'm still diving the same setup. The buoyancy characteristics are always the same.

Do you have to adjust for the warm saltwater vs. cool freshwater?

 

[jpsexton]

Do you have to adjust for the warm saltwater vs. cool freshwater?

You have to adjust your weighting for saltwater or difference in thermal protection but the buoyancy characteristics of the tank are the same. Going from a steel tank to an AL80 however changes the overall feel of your rig.