Tank basics for a beginner

[SMan]

I have spent some time looking at the postings on tanks, but obviously not all of them or I would be here for days. My family and I are new to scuba. There are four of use and this coming weekend will be our third trip to a local quarry. We typically dive both days and twice on each day. Due to one weekend being OW and the other weekend following buying gear for all of us (and my credit card is still smoking!) my LDS has provided tanks and free refills. Now we have to enter reality and deal with obtaining our own air. I have sufficient math skills to calculate how many dives it will take to make buying worthwhile. Also, I comprehend the basics on size and aluminum vs. steel. But there are way to many acronyms in the posts for me to accurately decode. Obviously, I will talk to the people at the LDS and those that dive with us, but I like to gather as much information as I can and this board seems very independent (is that an understatement?). A neutral source of information will be an added bonus as I work towards abusing the credit card some more.

Thanks in advance for any advice.

S

 

[The Chairman]

is an AL 80 at 3000 pounds. They will fill the vast majority of diving scenarios and are the easiest/cheapest to acquire. That being said, the tanks should be the very last items you buy (after BCs, regs, etc. etc). I hope this helps.

 

[art.chick]

So is your question whether to buy {3(people)x2(days)x2(dives)}=12 tanks????? Are you unable to drive to the shop for a fill after the 1st day?

Here's what sold me on buying tanks last year: we were running thru 1 tank on Saturdays in the pool, & 2 on the beach Sunday. At $8/tank/day, we had to have 2 tanks each (if we did a fil between days) At $100 each, the tanks paid for themselves in 8.25 weeks each. The average fill price is $4. We have a shop that gives free fills (so we definitely support it!)

I have Aluminum 63's, less air but i breathe pretty efficiently (this size may be easier for your daughters than the 80's.) Also, the little high-pressure steels are getting very popular (they have DIN valves, so they work with either European first stages, or you need to get an adaptor for an American reg.) Steels are recommended for people who want a negatively buoyant element to reduce the poundage on their weightbelt. With the amount of neoprene in a Chicago wetsuit, you will be at least tempted to consider this option.

 

[MikeS]

S,

I was certified in April and I have pondered the same issue for some time. I have purchased all of my equipment with the exception of primary tanks. I can only think of two situations where buying a tank(s), versus renting, makes sense. One, if you have your own air compressor. Two, if you cannot rent the type and/or size of tank you want.

By renting tanks I don’t have to worry about visual inspections and hydros or even where to store them. I pick um up from the LDS for $2 more each than an air fill! Have yet to not be able to rent as many tanks as I wanted on demand.

However, I have purchased a 30 cf pony and I am contemplating purchasing a 120 cf HP only because I cannot rent those sizes.

A word of advice, make sure you understand the implications of bottom time and buoyancy/shore weight before you decide which type (aluminum, low pressure steal, high pressure steal) and size to buy.

I think that tanks should be the last thing you worry about buying and it probably makes sense to get more experience before doing so. This is in no way a criticism of your experience, rather it is based on the fact that I’ve changed my mind several times as to the ideal configuration as I learn more and gotten more experience. There are several issues that you should resolve before making the type/size decision. For instance, do you typically run out of air or no decompression time first? Are you thinking about Nitrox training in the future? What size/weight of tank is manageable on the boat or shore?

Mike

 

[large_diver]

SMan,

Tank acronyms that I can think of:

AL = Aluminum

HP Steel = High pessure steel

LP Steel - Low pressure steel

PST = Pressed Steel (steel tank manufacturer)

DIN = a German acronym that stands for something "Deutsche Industrie Norm" (German Industry Standard...finally putting my college German to work....)....this term is usually used to described DIN valves. These are "female" valves that the first stage of the regulator screws into.

K-valve -- another term for the "standard" yoke valves you see on most tanks

H valve/Y valve -- valve shaped like an "H" or a "Y" that enable attachment of 2 first stages to a tank

For more info, try this "Tank FAQ" from scubadiving.com:
http://www.scubadiving.com/members/gearreviews.php?s=178

Part II of the Tank FAQ:
http://www.scubadiving.com/members/gearreviews.php?s=179

Tank links on diverlink -- note that the buoyancy data is not 100% accurate on this site.
http://diverlink.com/gear/valves.htm
http://diverlink.com/gear/tanks.htm

Hope all this is somewhat helpful.

 

[sheck33]

Most has been already said in earlier posts.
Yes tanks should be your last concern, you can always rent.
It is nice to buy when you dive a lot.
My humble advise would be to stay away from Aluminium tanks because of their lousy bouyancy characteristics, they are negative at the beginning and very very bouyant at the end of the dive which means you need a lot of weight to compensate.
Their only advantage is their cheapness.
I would also stay away from High pressure tanks because you are almost certain to end up with a lousy fill pressure because it takes time to get a high pressure tank filled to it's rated capacity.
In MHO the best tank to get is a low pressure steel. They have great bouyancy characteristics and you are sure to get a full tank no matter where you fill them. Not to forget the fact that when you overfill a low pressure tank by a few hundred PSI you will get MORE air as compared to overfilling a HP tank by the same amount.

i.e. (lets assume ideal gas behaviour)
LP 72 @ 2240 PSI = 72 cuft
HP 80@ 3500 PSI = 80 cuft

now overfill each by say 300 PSI (common practice, not recommended but done anyway)

now your LP 72 holds 2540/2240 x 72 = 81.6 cuft and your
HP 80 holds 3800/3500 x 80 = 86.8 cuft

a 9.6 cuft increase for the LP72 and a 6.8 cuft increase for the HP 80 plus the fact that it is a lot easier to fill the LP 72 to 2540 PSI than it is to fill the HP 80 to 3800 PSI!

 

[SMan]

First, I am not offended by the opinions that we get more experience. We are practicing this weekend at the quarry and the tanks may well wait to next year or later. Second, tanks are the last thing that I am looking at. We have been renting them from the LDS but it is difficult to make it back to the store before it closes on Saturday for refills for Sunday. Otherwise we have to rent 12 tanks (which seems silly) and eventually my wife will be certified. We have been using AL 80's (assuming I have the acronyms right) for our first 8 dives. And yes we have quite a bit of neoprene on here in Chicago, although I am currently using a 5mm. All the girls get cold easy. Also, typically my two daughters work as a team and carry one tank at a time together.

As for the nitrox, I have talked about it briefly with my instructor and others from the shop but I have not decided if we will utilize it here in the quarries - seems overkill. Perhaps some day in Lake Michigan or on vacations to warmer areas.

So far we only dive to a maximum of 60' and make sure to surface with at least 500 psi. We typically run out of no decompression time before we run out of air. Our breathing is getting more efficient and at the depth of the quarries time will be more of a limit than air supply.

Thanks again for the info/advice. Please keep sharing.
S

 

[chrispete]

Also, typically my two daughters work as a team and carry one tank at a time together.

Um, I was going to say something about diving 2x people on the same tank, but then it snapped that you were talking about carrying them on land and I can't delete this message.

 

[Walter]

SMan,

What exactly is your question?

sheck33,

Your numbers are off because of an incorrect assumption. A steel 72 does not hold 72 cu ft at it's working pressure. It holds approximately 72 cu ft (mine hold 71.4) with a 10% overfill. At their working pressure, they hold approximately 64 cu ft.

 

[SMan]

Walter,

I was looking for some basic understanding of the shorthand used for tanks on the board. My guesses were mostly correct, but clarification is always good. I got that from the postings below, but everyone's posting was very knowledgeable and went beyond my original question. So being the curious, knowledge seeking person that I am, I went right along with them. Basically, I am assuming that my family and I will continue renting AL 80s since that is what my LDS has the most of. But comments regarding buoyancy and weight (especially for my daughters) have been very helpful and will probably influence my purchase decision - when I feel that we are ready to own tanks.

Basically, I am a newbie looking for information and opinions to assist me in making the best decision for the majority of our dives. Which will probably be resh water dives in quarries and Lake Michigan.

As always any feedback is appreciated.
S