Which tank to buy?

[emttim]

Ok, so I've finally made up my mind to buy a tank, however, I have no idea which tank to buy. Should I get LP or HP? Whatabout size? My SAC is 0.63 cubic feet per min on average. I'd like to get a tank that I can get two dives out of before getting a fill on so I'm thinking of a Worthington/XS Steel HP 100. What do you guys think?

 

[sheck33]

Well, I dont have a list of buoyancy characteristics in front of me, but that is one thing you need to look at. Some other points that come to mind:

Steel tanks are heavier, requiring less weight on your weight belt.
Steel tanks have a smaller wall thickness resulting in more internal volume compared to an Al tank with the the outer dimensions.
But, steel tanks are a little more prone to rusting, with good care however this is not a real problem.
Steel tanks combined with diving in a wetsuit is generally not considered a wise thing to do.
Steel tank are considerably more expensive than Al tanks.

HP vs LP

In order for to have a full HP cylinder we must hit the water with 3500
PSI ( yeah and like that ever happens )
If I say in a HP 102 every cuft is equal to 34.31 PSI (3500/102=34.31)
And I overfill that cylinder to 4000PSI I would then have 116,58 cuft
available (4000/34.31=116.58)
But on the other hand if I took my LP cylinder and said each cuft is equal to 25.38 PSI (2640/104=25.38) and pumped that tank to only 3000 PSI it would give me 118.20 cuft of gas.
(3000/25.38=118.20) already I am gaining gas with out reaching an unobtainable goal in fill pressure.

So, my choice would be a steel LP cylinder in the 100 cuft range assuming you dive a drysuit.

Now to contradict myself here, I use a LP 104 when I dive a single tank but use the HP E8 130's for my doubles, not by choice really since they replaced the LP104 with the HP130, but see, if I fill both tanks to 3000 psi, the LP104 contains more gas.

 

[Beachlover]

Well, I dont have a list of buoyancy characteristics in front of me, but that is one thing you need to look at. Some other points that come to mind:

Steel tanks are heavier, requiring less weight on your weight belt.
Steel tanks have a smaller wall thickness resulting in more internal volume compared to an Al tank with the the outer dimensions.
But, steel tanks are a little more prone to rusting, with good care however this is not a real problem.
Steel tanks combined with diving in a wetsuit is generally not considered a wise thing to do.
Steel tank are considerably more expensive than Al tanks.

HP vs LP

In order for to have a full HP cylinder we must hit the water with 3500
PSI ( yeah and like that ever happens )
If I say in a HP 102 every cuft is equal to 34.31 PSI (3500/102=34.31)
And I overfill that cylinder to 4000PSI I would then have 116,58 cuft
available (4000/34.31=116.58)
But on the other hand if I took my LP cylinder and said each cuft is equal to 25.38 PSI (2640/104=25.38) and pumped that tank to only 3000 PSI it would give me 118.20 cuft of gas.
(3000/25.38=118.20) already I am gaining gas with out reaching an unobtainable goal in fill pressure.

So, my choice would be a steel LP cylinder in the 100 cuft range assuming you dive a drysuit.

Now to contradict myself here, I use a LP 104 when I dive a single tank but use the HP E8 130's for my doubles, not by choice really since they replaced the LP104 with the HP130, but see, if I fill both tanks to 3000 psi, the LP104 contains more gas.

Why do you say that steel tanks combined with diving in a wetsuit is generally not considered a wise thing to do?

 

[RonFrank]

Why do you say that steel tanks combined with diving in a wetsuit is generally not considered a wise thing to do?

It's likely a DIR thing. Steel tanks require two forms of lift in case one fails... However I don't subscribe to that thinking in this case. Weight is weight regardless of where it resides, so if you can trade some weight off the belt for tank weight, IMO do so as needed.

However the bottom line is that you need to be able to swim up your gear. It does not matter how much weight you have, more to the point that you are not overweighted by more than a couple lbs, and you can swim the entire thing to the surface in the event of a BC failure.

For example, If I dive a Steel tank, I can remove 6lbs of lead from my belt or so. If I did not have 6 lbs of lead on my belt, that could be an issue as I would be overweighted with a Steel tank. However I dive with 10lbs in salt, so if I rent a Steel tank, I just loose the weight off my belt which is not a bad thing.

You don't want to be overweight. I am less concerned about where the weight is than I am about how much I carry!

 

[Beachlover]

It's likely a DIR thing. Steel tanks require two forms of lift in case one fails... However I don't subscribe to that thinking in this case. Weight is weight regardless of where it resides, so if you can trade some weight off the belt for tank weight, IMO do so as needed.

However the bottom line is that you need to be able to swim up your gear. It does not matter how much weight you have, more to the point that you are not overweighted by more than a couple lbs, and you can swim the entire thing to the surface in the event of a BC failure.

For example, If I dive a Steel tank, I can remove 6lbs of lead from my belt or so. If I did not have 6 lbs of lead on my belt, that could be an issue as I would be overweighted with a Steel tank. However I dive with 10lbs in salt, so if I rent a Steel tank, I just loose the weight off my belt which is not a bad thing.

You don't want to be overweight. I am less concerned about where the weight is than I am about how much I carry!

Thanks for your reply. Still curious to read what sheck33's reason. I dive my 7mm and a steel 95 all the time,ten years and 550 dives.Never had any problems with my setup.Don't want to hijack this thread any longer, sorry to the OP.

 

[emttim]

Well, I'm diving with a steel, period. I hate aluminum.

I'm aware of the buoyancy characteristics...that's why I want a steel. So you're saying LP is a better investment, basically?

 

[sheck33]

Why do you say that steel tanks combined with diving in a wetsuit is generally not considered a wise thing to do?

It depends on one's particular configuration. But I have to admit that what I was thinking didnt make it into my post, I was in particular thinking that diving steel doubles should not be done in a wetsuit as they are far too heavy to swim to the surface in case of a wing failure. As RonFrank mentioned, keypoint is that you can swim your rig to the surface in case your wing fails. I think it is essential to have some ditchable weight when diving steel tanks in a wetsuit. Sorry for the confusion.

 

[Beachlover]

It depends on one's particular configuration. But I have to admit that what I was thinking didnt make it into my post, I was in particular thinking that diving steel doubles should not be done in a wetsuit as they are far too heavy to swim to the surface in case of a wing failure. As RonFrank mentioned, keypoint is that you can swim your rig to the surface in case your wing fails. I think it is essential to have some ditchable weight when diving steel tanks in a wetsuit. Sorry for the confusion.

Thanks for replying. I don't dive doubles, so I have no knowledge of such.I agree that you need to have ditchable weights.

 

[El Orans]

It's likely a DIR thing.

True but we're not talking about doubles here. Steel doubles and a wetsuit are not recommendable.

AFAIK, there's no such issue regarding single steel tanks and wetsuits. Heck, 99% of all divers here use that kind of set-up.

 

[zen_man]

The last 2 pages of this thread I believe sum it up well: http://www.scubaboard.com/forums/tanks-valves-bands/226400-lp-vs-hp-question.html

I'm personally a fan of HP 80s and 100s. I like the compactness of the 80 and how an HP 100 fits for me. I'm also not big on overfilling LP tanks. I know it is somewhat common practice in certain areas, but it's just not worth it to me chance wise.

just my 2 psi,

:zen: