Tank Questions

[MaverickNH]

Newbie diver renting AL80s with a few tanks questions:

1. Is it worth buying an old used AL80 air tank, near it's lifetime but still passing, to use in maintenance, like testing the reg/BC before heading out from home (at site, I'll pre-dive check with my actual dive tank, of course), blowing out my reg once well-rinsed at home, putting some dry air in my BC once washed, etc?

2. I'll eventually buy a few tanks for my local diving. What factors to consider in cf volume? I'm leaning toward steel as a long-term investment and maybe a 120cf HP tank. Why? On the upside, cost/cf appears to be lower than 80 & 100 (not much lower for 140cf) and empty weight/cf appears lowest of 80, 100, 120, 140 tanks. (based on XS Scuba tank prices).

On the downside, buoyancy full vs buoyancy empty appears lowest for 80cf (6lb difference) and highest for 140 (9.7lb difference) and in-between for 120 (9lb difference). Also, double 120s are 10lb heavier empty than double 100s (but I figure if I can carry 66lb, I can carry 76lb).

BTW, I'm using a ScubaPro MK25/S600 reg for single-tank (and would explore options for dual-tanks later). My ScubaPro Knighthawk BC has a 2-tank setup option, although probably not optimal for that purpose.

I know I'm not considering all those many factors like what type of diving (shore, boat, wreck, cave, etc) and depths, but am looking for a flexible system, initially for shore & boat to 130ft, some wrecks with no overhead/penetration.

Thanks for the feedback.

 

[ajtoady]

The reason the buoyancy swing is lower for an 80 vs a 140 is air has weight. The tanks themselves do weigh different but, when you carry more air you carry more weight. A steel tank properly cared for will more than likely outlast an aluminum. Steel tanks are also more forgiving in overfills and physical abuse.

 

[mathauck0814]

1. Is it worth buying an old used AL80 air tank, near it's lifetime but still passing, to use in maintenance, like testing the reg/BC before heading out from home (at site, I'll pre-dive check with my actual dive tank, of course), blowing out my reg once well-rinsed at home, putting some dry air in my BC once washed, etc?

IMO, no. Used AL80 tanks should be cheap enough to get a good one. I'm not sure how you'd know if it were near its useful end, but you'll have issues getting fills if you can't get it through viz/hydro. Better to just own tanks for diving and use those (or rinse your regs while you still have your rental tanks, maybe?).

2. I'll eventually buy a few tanks for my local diving. What factors to consider in cf volume? I'm leaning toward steel as a long-term investment and maybe a 120cf HP tank. Why? On the upside, cost/cf appears to be lower than 80 & 100 (not much lower for 140cf) and empty weight/cf appears lowest of 80, 100, 120, 140 tanks. (based on XS Scuba tank prices).

The size of your tank should be dictated by how much air you need for the dive you're planning to do. You should have learned about calculating your SAC. It may be helpful to see what other people in your area are diving and talk to them about it as well.

On the downside, buoyancy full vs buoyancy empty appears lowest for 80cf (6lb difference) and highest for 140 (9.7lb difference) and in-between for 120 (9lb difference). Also, double 120s are 10lb heavier empty than double 100s (but I figure if I can carry 66lb, I can carry 76lb).

What you need in terms of buoyancy characteristics of the tank will vary based on your personal physiology and exposure equipment.

BTW, I'm using a ScubaPro MK25/S600 reg for single-tank (and would explore options for dual-tanks later). My ScubaPro Knighthawk BC has a 2-tank setup option, although probably not optimal for that purpose.

Correct - not optimal for doubles.

 

[k ellis]

One thing to keep in mind when buying tanks is how will it be with your traveling needs. If you use a 80 CF or less then your BCD strap will be accomodating for most tank rentals. This really is not a problem though as bcds and BPWs are adjustable. It just adds one tiny extra step. As others have mentioned though I am curious to know how you would know a tank is nearing its useful life. There are tanks out there that shops will not VIP because they are so old and made out of aluminium (Dont know the details why I just know they say tanks made before xx/19xx can not be VIPed or Hydroed.)

Though these older tanks have reason to not be inspected many of them would be just as safe today as the day they were purchased. Consider tanks like cars in a lot of ways. You can buy a new one and baby it and take really good care of it and it last many years or you can buy one and only fill it as needed then store it out in an old shed thats drafty and allows the elements to encroach the tank and only get a few good seasons from it. Its entirely up to the owner how long typically a tank will last.

 

[joel smith]

Buy you some Worthington Steel 100 tanks and dive dive dive , everything else will work itself out.

 

[TSandM]

Unless you have a way to fill tanks without taking them to a shop, you will have to keep any tanks you own in viz and hydro, so buying a tank which is very old or the wrong alloy (and therefore cheap) may prove a false economy. Having a tank around at home with gas in it, however, is quite handy for many things, including flat tires

As far as what tank you should buy and dive, in cold water, steels have a significant advantage, because what you probably want is to minimize the total weight you carry. Needing five pounds more ballast to sink an Al80 (which is not a light tank to begin with) is not fun. In terms of pounds of tank weight in relation to tank capacity, the HP steels have the edge -- LPs weigh more for the same volume. LP tanks are usually cheaper, though, and although it is not a problem in my area, in some places people seem to have problems getting good 3400 psi fills, which the HP tanks require to deliver their stated volume.

I wouldn't base what you buy to dive singles on what might make good doubles later. You're likely to want a single tank rig around anyway, and buying used doubles that are already assembled is easier than putting your only tanks together.

 

[Blue Sparkle]

There are tanks out there that shops will not VIP because they are so old and made out of aluminium (Dont know the details why I just know they say tanks made before xx/19xx can not be VIPed or Hydroed.)

Though these older tanks have reason to not be inspected many of them would be just as safe today as the day they were purchased.

I thought the reason the pre-1990 (it may be a date in the late 80's, but I think we are talking about the same thing) aluminum tanks were on the "negatory" list is because of potential sustained load cracking of that specific alloy. If that is the case, I don't see that they would be "just as safe today as the day they were purchased."

Now that said, I have not researched it enough to know if the whole thing is biased or proven to be untrue; just that I have read about the "given" reason being the potential cracking. If anyone can speak to this, I'm interested.

... or you can buy one and only fill it as needed then store it out in an old shed thats drafty and allows the elements to encroach the tank and only get a few good seasons from it. Its entirely up to the owner how long typically a tank will last.

Not that I would just throw my tank out in the snow and rain for storage, but can drafts and such in a shed shorten the life to a few seasons? (Yes, I'm tank shopping, and yes I would be storing them in a shed.)

 

[markmantei]

The size of your tank should be dictated by how much air you need for the dive you're planning to do. You should have learned about calculating your SAC. It may be helpful to see what other people in your area are diving and talk to them about it as well.

Agree, in a perfect world we would all dive the tank best suited for the dive. That said tanks are a long term investment, and can be fairly pricey, I would argue that it is better to have too much tank than too little. Personally I decided to get a couple of HP130's. They are more air than I need for any diving I'm doing now, but can grow with me and even be turned into a twin set down the road.

 

[RTee]

As somebody else mentionned, tanks are long term investment. If you can afford steel, then I would opt for one right off the bat rather than look for a used 80 AL as they usually contained more and are more efficient from a weight perspective . I also think you can get a HP 120 for the same price as a HP100 therefore I would opt for the 120s. Air to a diver is like fuel to an airplane...you never carry too much.

 

[mathauck0814]

No offense or anything, but tanks are a pretty minor expense in the grand scheme of this activity.