Double Tank Setups

[Fishbone]

Being new to dive I have a lot of questions but after reading some of the threads I have questions about double tank setups. It seems (in my are at least) all double tank ridgs are steel and seems the most common are steel 72's pressure rated to 2250 (I think). Why not aluminum? Why are some steel tanks rated lower? Why not higher pressure cylinders? Seems if you are going to lug around 75+++ pounds on your back you would go for the most amount of air.

Fishbone

 

[Lamar Jr]

Your question is probably more appropriate for the Equipment forum than Introductions.

Good luck with question and enjoy the board. There is plenty to learn here about cylinders and many other subjects.

Dive safe and often.

 

[DA Aquamaster]

I use steel 72's as they are common, inexpensive, relatively lightweight and have good bouyancy traits. Steel 72's or AL 80's are in many respects a very good choice for diving with a wet suit as they are not excessively negative even when full. Twin AL80's are used quite often and are in fact very stable in the water due to their generally positive bouyancy.

The downside with twin steel 72's is that you only have a total of about 95 cu ft available for planning purposes if you use rule of thirds air management. Al 80's are not much better at about 103 cu ft. But this works well for the dives I do and is adequate for a dive to 150 ft for 20 minutes which is about all I ever ask of them.

Most of the other steel tanks offer more air capacity but are substantially heavier and normally are more negative when full and still slightly negative when empty making redundant floatation in the form of both a BC/Wing and drysuit nice to have.

LP steel tanks offer some advantages in terms of being able to get good fills almost anywhere, and they make more sense for cold water diving than a high pressure steel tank. And some divers seeking serious air capacity will overfill steel tanks 10-20% or more. That is less of an option with a HP steel tank given the limits of commonly encountered compressors.

 

[armyscuba]

You have much to learn Young Jedi...are You inquiring about doubles because You consume "MUCH" Air..? I only ask because You say You are new to the sport. There are many ways in which to configure doubles. Many reasons as to why Divers use them. The list is endless. I agree though..You should probably pick another forum..Start the thread all over..I'm sure We'd all jump in...

 

[DandyDon]

Howdy!

Welcome to SB!! :happywave Put us in your computer's favorites and check in often. This is a great place to learn, compare, argue

don

BTW - it would really help if you'd fill out your Profile - so we can respect your training and experiences, or be courteous if you're a newbie?!

 

[IndigoBlue]

Being new to dive I have a lot of questions but after reading some of the threads I have questions about double tank setups. It seems (in my are at least) all double tank ridgs are steel and seems the most common are steel 72's pressure rated to 2250 (I think). Why not aluminum? Why are some steel tanks rated lower? Why not higher pressure cylinders? Seems if you are going to lug around 75+++ pounds on your back you would go for the most amount of air.

Fishbone

Welcome to Scubaboard, Fishbone.

Double tanks can be aluminum or steel. And the steel can be high pressure steel or low pressure steel.

Double aluminum tanks are more popular in warm water areas than in cold. But you see them all in all temps of water.

Rental tanks are normally single aluminum 80s or single steel 72s. These used rental tanks then get sold off by the scuba store every few years, and therefore there are a lot of bargains available in alum 80s and in steel 72s.

That is probably why you see a lot of 72s, and also why it is common to see steel 72s paired as doubles.

What size tanks you buy or rent, whether aluminum or low pressure steel or high pressure steel, depends on what you plan to do underwater. If all of your buddies that you dive with have a certain sized tank or tanks, then you will likely want to get the same size as them. It does not do you a lot of good to wear the largest tanks, and it does not do them any good if you have the smallest. It is a team thing.

So remember to check with your buddy or buddies, before you buy tanks.

My overall recommendation for a single tank is a steel 72. I perfer Fabers. Whether you need doubles or not depends on what you plan to do, and what your training level is.

 

[Don Burke]

Being new to dive I have a lot of questions but after reading some of the threads I have questions about double tank setups. It seems (in my are at least) all double tank ridgs are steel and seems the most common are steel 72's pressure rated to 2250 (I think). Why not aluminum? Why are some steel tanks rated lower? Why not higher pressure cylinders? Seems if you are going to lug around 75+++ pounds on your back you would go for the most amount of air.

I have double steel 72s rated to 2250, and they are the exception rather than the rule. I also have double aluminum 80s.

Believe it or not, cubic foot for cubic foot, aluminum tanks often end up making you weigh more than steel tanks.

I happen to think diving dry with double AL80s sucks big time. Your mileage may vary.

Different tanks are designed for different things. If I was running a dive shop, I wouldn't have any high pressure tanks in the rental fleet.

High pressure presents problems with getting good fills in some areas. Many don't have those problems.

You go for enough gas to get the dive done safely. That isn't the only consideration on selecting tanks. It never has been for me.

 

[TLada]

I've had problems getting my HP steel's filled to max 3500 at dive shops. It seems they dont want to push their compressors any more than they absoluely have to. Your better off going with LP to get the fills you can count on. You will have to carry extra weight... but thats the price of predictable fills.
I think the Faber 100 represent the best trade off between capacity, size, fill rate, and usefull volume.