Types of tanks

[Texasdiver2]

I have done a search and cannot find the info I want or if it is there, I don't understand it.

I read about various types of tanks that are available and want to see exactly what the various options for tanks are. Size of tank. Composition of the tank. Weight of tank. What are the advantages/disadvantages of each.

I have only ever used the tanks that are available on a dive boat. I do not own tanks nor do I anticipate purchasing tanks.

I just want to know when a dive operator says that certain types of tanks are available I will be able to make an informed choice.

Also about tanks, what exactly is psi telling me? I believe that I have only used Al 80 tanks in the past. A full tank reads about 3000 psi on my guage. I realize this is not telling me the amount of air but the pressure it is under inside the tank, correct?

So do other tanks have different psi levels to indicate when the tank is full?

thanks for any and all info.

Texasdiver2

 

[DA Aquamaster]

Here are a few links that may help.

http://www.diverlink.com/gear/tankspecifications.htm

http://www.diverlink.com/gear/tanks.htm

Tanks use various pressures when "full". They vary from 2250 to 2475 for older steel 72's to 2400 and 2640 for newer low pressure steel tanks, 3000 to 3300 for newer aluminum tanks and 3500 psi or more for high pressure steel tanks.

One cu ft of air is about 35 psi in a steel 72, and about 39 psi in an aluminum 80 so there is some variance between tank designs.

 

[Seadiver5]

If I am not mistaken capacity in Cu. Ft. of air = Volume X Pressure.

To increase Cu. Ft. you can only increase pressure not volume of a given tank.

That is why low pressure tanks that hold in the 2400 psi range and are so much larger in size than the High pressure tanks of equal cu. ft. that usually hold in the 3500 psi range.

A common mistake made by many new divers is that they train on the Al. 80 at 3000 lbs. then they purchase an LP tank and where a AL 80 1/3 gone at 2000 psi the LP tank is still nearly full. what I am saying is that it is hard to get some divers to understand that they need to adjust their thinking when it comes to Cu. Ft. of available air. They get the PSI stuck in their minds and can't get passed that.

As for understanding every tank out there. Don't bother.
I simply default to Steel if it is available but most Rental tanks are going to be AL and most likely always will be due to the fact that they are less work to maintain.

Kevin Parkhurst
IDEA Instructor 3402

 

[Warren_L]

You also need to factor in the temperature. The same mass of air in a tank will change pressure as the temperature changes.

 

[TwoBitTxn]

I have done a search and cannot find the info I want or if it is there, I don't understand it.

I read about various types of tanks that are available and want to see exactly what the various options for tanks are. Size of tank. Composition of the tank. Weight of tank. What are the advantages/disadvantages of each.

The two choices of tank composition are aluminum and steel. The Aluminum 80 is the most common tank in recreational use in the US and Mexico. A full aluminum tank is negatively bouyant. As you breath the air from the tank it becomes more bouyant. Most (not all) aluminum tanks become positively bouyant (they float) before they reach 500psi. Most steel tanks do not become positively bouyant thus you can reduce the amount of weight you carry.

Also about tanks, what exactly is psi telling me? I believe that I have only used Al 80 tanks in the past. A full tank reads about 3000 psi on my guage. I realize this is not telling me the amount of air but the pressure it is under inside the tank, correct?

More than likely you have only used an Al 80.

Think of it this way. The air in your car tires is at a certain pressure. Assume the MFR states that a tire is full at 32psi. The tire looks full. The volume of air in the tire exerts an outward pressure of 32psi. A flat tire has no air, thus no pressure. Reduce the volume of air in the tire and you reduce the pressure.


HTH

TwoBit

BTW... Welcome, watch the Texas Swamp Divers board and come dive with us when you can.

 

[Warren_L]

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Think of it this way. The air in your car tires is at a certain pressure. Assume the MFR states that a tire is full at 32psi. The tire looks full. The volume of air in the tire exerts an outward pressure of 32psi. A flat tire has no air, thus no pressure. .
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Still 1 ata, but you probably meant no pressure in gauge.

 

[DA Aquamaster]

If I am not mistaken capacity in Cu. Ft. of air = Volume X Pressure.

To increase Cu. Ft. you can only increase pressure not volume of a given tank.

That is why low pressure tanks that hold in the 2400 psi range and are so much larger in size than the High pressure tanks of equal cu. ft. that usually hold in the 3500 psi range.

What you are saying is generally true for comparing a steel tank to a steel tank. For example: An LP 80 holds 80.6 cu ft at 2640 psi while an HP 80 hold 82.1 cu ft at 3500 psi and only 64.5 cu ft at 2640. Both are the same 7.25" diameter but the HP 80 is 5 inches shorter.

However this is not entirely true when comparing steel to aluminum. An AL 80 is taller than a steel 72 and larger in diameter but actually has less internal volume than a steel 72.

The AL 80 is larger in its external dimensions because the wall thickness is greater at about 1/2 inch compared to about 1/4 inch for a steel tank. That greater volume of aluminum is ultimately what is responsible for the increased bouyancy of the tank and it also makes the tank heavier out of the water.

 

[Texasdiver2]

xxsx

 

[Ari]

That 12 liter AL tanks and 15 lliter St tanks will be the most common.

Different tanks have different charectaristics, with regard to dry weight, buoyancy, amount of gas stored etc. Naturally, they will effect other diving conditions, such as required weight, dive time, etc.

You are right, the availability of different tanks is confusing. Nevertheless, as you do some more research, you will better understand the issues.

Ari