Tank sizing, HP & LP?

[GrumpyOldGuy]

The terms "outstanding" or "just good enough" are relative. It depends on what you want in a tank.

It's true that an HP steel 100 has more capacity than an AL80 - that's apparent even in their names. And these are the natural tanks to compare, since they are dimensionally close to the same size.

For what it's worth, most shops willing to fill a steel to 3442 psi are also willing to fill AL80's to 3300 psi, depending on some factors... Making the capacity difference less. But that's not really the point.

The point is that the tanks have other characteristics that are more important - like inherent bouyancy. Steel tanks are inherently more negatively bouyant than aluminum tanks, which can be a good thing or bad thing - it depends on it's application and how it changes the diver's trim.

Another important factor is the tank's resistance to corrosion. For the same reason that boat, dock, and boat trailer parts are better designed out of stainless steel or aluminum than galvanized steel, tanks exposed regularly to salt water tend to experience less corrosion issues if they're made of aluminum instead of galvanized steel (I've never seen a stainless steel tank and suspect that the material wouldn't do well with the pressure).



Agreed. But if you're running out of air, get a larger tank - or better yet, multiple tanks (or even better yet, reduce your SAC rate - it's usually free and has a lot of additional benefits). An aluminum 120's capacity exeeds that of an HP100, and has basically the same bouyancy characteristics and corrosion resistance of an AL80. For that matter, AL100's are also available, and exceed an HP100's capacity when filled to 3300 psi.

I'm not "against" HP steel tanks - I'm just saying that they should match the application and that their unique characteristics aren't a benefit in every situation. Sometimes they're great, and sometimes a different tank is a better idea.

By default, if you set up your rig to handle aluminum 80's (cam band adjustment and weighting), then you'll be most likely to be set up correctly at the dive site, assuming that you're renting tanks. Of course, that doesn't apply to every geographical area - some areas favor a certain "style" of tank... But in the Western hemisphere, the AL80 is the standard and therefore should be the default tank to set up your rig for.

...With regards to owning a tank (the OP's original question), the above doesn't apply - but if you're going anywhere and renting tanks, you'll generally have to modify your rig if you don't normally dive AL80's.

Comparing an overfilled AL80 to a normally filled HP100 is apples and oranges. Most LDS's I know wont overfill much if at all. Especially AL tanks.

I would be interested in your AL120 - I have never seen one nor found them listed for sale. Any specifications?

As for the AL100 you suggested, the Catalina is 46lbs dry (vs 32lb for the HP100) - you are kidding right? My back hurts just thinking about it. Not sure what trim problem that is going to fix unless you are diving with no exposure suit.

 

[Deep South Divers]

Comparing an overfilled AL80 to a normally filled HP100 is apples and oranges. Most LDS's I know wont overfill much if at all. Especially AL tanks.

It's not an overfill - well, sorta. There's a certification rating called "VIP+." It means that the tank is certified to handle a 10% overfill - which, technically isn't an "overfill" if it's certified.

...But yeah, it's 10% over service pressure. Interestingly, "service pressure" is the pressure inside the tank when it's got it's rated capacity... An AL80 is generally 77.7 cuft at it's service pressure, 3000 psi.

If a tank has been "plused," then you can fill to 3300 psi... Which would be 85.47 cuft of gas.

I don't know if other tanks can be "plused" in the same way, but it's worth asking about if you're interested in the "VIP+" program.

For what it's worth, burst disks and plugs are usually designed to pop at around 4200 psi - depends on the manufacturer. My point is that it's a far cry from 3300 psi.

...And when tanks are hydrostatically tested ("hydroed"), they're tested at a pressure of 10,000 psi... So an extra 300 psi is hardly threatening, even in aluminum tanks.

I would be interested in your AL120 - I have never seen one nor found them listed for sale. Any specifications?

Heh - nope, ya caught me... I was incorrect. The "AL120" that I thought a buddy of mine was diving is actually a steel 120. Doh! Sorry for the misinformation.

The largest aluminum tank I've found is an AL106, high pressure, and apparently a "limited production" tank... I have seen it on a couple of charts, but never seen one in person (or for sale, for that matter): SCUBA diving equipment and gear sales store

For what it's worth, a lot more tank information can be found at How to Select a SCUBA Tank - Dive Gear Express . Caution: They, too, are incorrect in saying that an AL100 is the largest aluminum tank available, although in all fairness the "limited" 106 may be a brand new thing.

I also caution that while a good wealth of information, they ARE trying to sell tanks, and thus tend to favor pricier tanks... And are somewhat biased toward HP steels. Nonetheless, their information is otherwise very good, as far as I can tell.

As for the AL100 you suggested, the Catalina is 46lbs dry (vs 32lb for the HP100) - you are kidding right? My back hurts just thinking about it. Not sure what trim problem that is going to fix unless you are diving with no exposure suit.

The Luxfer AL100 is 41 pounds, and Faber's version of the steel HP100 is 39 pounds. You're quite selective in which tanks you're comparing.

Nonetheless, you're right - aluminum tanks are generally slightly heavier than steels while being more bouyant than steels.

...But that doesn't make them the right choice in every situation - for some of the other reasons that I mentioned.

By the way - you're dramatically exaggerating the difference in dry tank weight. The gas itself weighs almost 8 pounds... Which means the difference between a full tank and an empty tank is eight pounds. If 14 pounds causes you backbreaking agony, what would another 8 pounds do to you?

The "trim" issue is what I mentioned in my last post - the "finicky" part. Instead of me telling you about it and you arguing with me thereafter, how 'bout you go get wet and try it out for yourself?

 

[Splitlip]

New one on me. I have never heard of a plus rating for aluminum tanks. Only LP steel.

 

[texdiveguy]

Drop the whole idea of HP100 or the worst tank on the market a LP95, simply go with a LP85 and you will be SO much happier!!

 

[Papa_Bear]

With my LP95 I can drop 10lbs of my belt and with a 2750psi fill I am at 110cft and if your a caver you just fill it to 3800psi For a single tank configuration I don't think you can find a better tank!

 

[Splitlip]

Drop the whole idea of HP100 or the worst tank on the market a LP95, simply go with a LP85 and you will be SO much happier!!

Yeah, when I dumped my LP 98's (cause of the 8" Dia), I passed on the LP 85's cause I was having trouble getting them pumped. Otherwise, I'd have done the 85's.

 

[Splitlip]

It's not an overfill - well, sorta. There's a certification rating called "VIP+." It means that the tank is certified to handle a 10% overfill - which, technically isn't an "overfill" if it's certified.

...But yeah, it's 10% over service pressure. Interestingly, "service pressure" is the pressure inside the tank when it's got it's rated capacity... An AL80 is generally 77.7 cuft at it's service pressure, 3000 psi.

If a tank has been "plused," then you can fill to 3300 psi... Which would be 85.47 cuft of gas.

I don't know if other tanks can be "plused" in the same way, but it's worth asking about if you're interested in the "VIP+" program.

For what it's worth, burst disks and plugs are usually designed to pop at around 4200 psi - depends on the manufacturer. My point is that it's a far cry from 3300 psi.

...And when tanks are hydrostatically tested ("hydroed"), they're tested at a pressure of 10,000 psi... So an extra 300 psi is hardly threatening, even in aluminum tanks.



Heh - nope, ya caught me... I was incorrect. The "AL120" that I thought a buddy of mine was diving is actually a steel 120. Doh! Sorry for the misinformation.

The largest aluminum tank I've found is an AL106, high pressure, and apparently a "limited production" tank... I have seen it on a couple of charts, but never seen one in person (or for sale, for that matter): SCUBA diving equipment and gear sales store

For what it's worth, a lot more tank information can be found at How to Select a SCUBA Tank - Dive Gear Express . Caution: They, too, are incorrect in saying that an AL100 is the largest aluminum tank available, although in all fairness the "limited" 106 may be a brand new thing.

I also caution that while a good wealth of information, they ARE trying to sell tanks, and thus tend to favor pricier tanks... And are somewhat biased toward HP steels. Nonetheless, their information is otherwise very good, as far as I can tell.



The Luxfer AL100 is 41 pounds, and Faber's version of the steel HP100 is 39 pounds. You're quite selective in which tanks you're comparing.

Nonetheless, you're right - aluminum tanks are generally slightly heavier than steels while being more bouyant than steels.

...But that doesn't make them the right choice in every situation - for some of the other reasons that I mentioned.

By the way - you're dramatically exaggerating the difference in dry tank weight. The gas itself weighs almost 8 pounds... Which means the difference between a full tank and an empty tank is eight pounds. If 14 pounds causes you backbreaking agony, what would another 8 pounds do to you?

The "trim" issue is what I mentioned in my last post - the "finicky" part. Instead of me telling you about it and you arguing with me thereafter, how 'bout you go get wet and try it out for yourself?

Check out this.
Scuba Cylinder Specifications from Tech Diving Limited - 928-855-9400

The "HP" faber you see out there now for the most part is the FX. 34#

And I don't see an aluminum 106?

 

[texdiveguy]

Yeah, when I dumped my LP 98's (cause of the 8" Dia), I passed on the LP 85's cause I was having trouble getting them pumped. Otherwise, I'd have done the 85's.

Sorry to hear that....there should be NO difference in tech pumping any LP steel tank. Allot of recreational shops just fill to the + limit, but allot of shops located in cave/wreck area's will over fill an LP85 to say 3400 easy. My standard fill on my LP85's is 2800 to 3000psi.

 

[Splitlip]

Sorry to hear that....there should be NO difference in tech pumping any LP steel tank. Allot of recreational shops just fill to the + limit, but allot of shops located in cave/wreck area's will over fill an LP85 to say 3400 easy. My standard fill on my LP85's is 2800 to 3000psi.

Agree.

My shop at the time was reeling from an Al 80 that blew up and injured an employee, so they stopped pumping LPs. (apples and oranges I know). So I sold my 98's to caver bud who has no trouble in cave country. I have since (changed work locations) found a shop which has no issues.

 

[gcbryan]

I tried searching for this, and frankly I didn't even really know what to ask for in the search criteara, so I will just ask it and please forgive me if it was recently answered.

I am going to be getting a steel tank (or two -- as singles, I always like to have a apare) for when I wear my drysuit. I am planning on getting one with DIN with the yoke adapter (my first stage is yoke).

My question comes in about HP vs LP.

I understand that a 100 CF tank is going to contain 100 CF of air (more or less), so that the HP vs. LP comes down to a matter of size and weight.

I am trying to reduce the amount of lead that I am carrying by switching to steel, and also to enjoy the improved buoyancy characteristics of steel over aluminum. That is my stated goal in the switch.

I am thinking about getting either a 100 HP or 95 LP.

Is the 95 LP significantly heavier than the 100 HP?

If my stated goal is to replace lead with tank weight, would I be better off with a LP 95 (which is also easier on the rest of my rig)?

Thanks.

Here is what I considered when I went from aluminum to steel.

Locally Faber LP 95's were common as were PST HP 119's. From what I remember Faber's were very heavy (when compared to other 95's).

If you are going to have a bigger tank and higher pressure fills are available in your area why not go with the larger HP tank? If you get a good fill great and if you don't you will still have as much air as the LP 95's.

There are different configurations of the 119's as well. There is a wider tank that isn't as tall and a taller tank that isn't as wide. Even though I'm reasonably tall (6'1") I still prefer the shorter and wider 119. I've tried both as well as the 130's.

So, whatever you get try to find a friend with that same tank and actually dive it before buying anything.

I'm diving in cold water with a drysuit and a lot of undergarments and then I was using a lot of weight on my weight belt. I was able to take of about 8 lbs with the single HP 119 (and another 5 lbs or so with a SS BP).

This made a lot of difference in comfort. It's easier to carry weight on the back than on the waist. We have dives that get deep fast so going for 119 vs 95 was a no brainer for me. It depends on your local diving though. If you can't get get below 60 feet then maybe 119 is overkill. I like having extra air and carrying a 119 is just perfect for me.

Regarding DIN...if a lot of your diving is local then you might want to just convert your first stage to DIN. It's usually easy and just buy a yoke adapter for vacation. This is what I did. DIN (to me is a lot nicer), no more constantly having tank o-rings blow out just before a dive. It just seems like a better way to connect tank and first stage as well.

The DIN to yoke adapter is kind of bulky and if most of your diving is actually vacation diving you may not want to go that route otherwise just convert your first stage to DIN and be done with it. For most first stages once you do the conversion it's just as seemless as if you bought it that way...in other words it's not some bulky adapter.

Using a bulkier adapter for the occasional vacation dive is not a big deal.

I end many dives with 1,000 psi in the tank but the occasional dive uses more of the capacity which is perfect in both cases.

Most dives end or at least get shallower because I go into deco for a bit and then need to shallow things up. With Nitrox in many cases my profile would be the same but I just wouldn't be getting into a little deco. This is deco due to faster compartments due to depth rather than due to time as in long 60 foot dives.

So it all just depends on your most common diving environment. At least consider whatever the more frequent divers in your local area are diving...there's probably a reason for their choices.