HP vs. LP Steel tanks. Whats the difference ?

[Diverdown269]

I'm sure this question has been asked before, but I was not able to find a thread for it.

I am unclear on the difference between HP and LP tanks. I know HP are rated at 3442 and LP at 2400. I have heard that a LP108 is basicly the same as a HP130

108 at 2400PSI vs. 130 at 3442PSI

The 130 must have quite a bit more air in it then the 108. The point of doubles is to carry more air, so are LP tanks for shorter/shallower dives, and HP for deeper/longer dives ? What am I missing here ?

 

[CT Sean]

HP vs LP is just that: high pressure vs low pressure tanks. The number is the cubic feet of air that the tank holds at that pressure so an LP108 means that there is 108 cf (cubic feet) in the tank when the pressure equals 2400 psi. Same for your HP130: 130 cf at 3442 psi

Regarding the LP108 "basically the same" as an HP130, they are about the same physical size - 8" diameter by 26" long, but the HP130 has more air in it (22 cf more) since it is at a higher pressure.

Others will have to give info on what tanks are better for different types of dives, but it's not as simple as LP for one and HP for another

 

[PerroneFord]

HP and LP tanks are constructed of different materials, they have different buoyancy characteristics, they don't weigh the same even empty.

And in some places (like where I live) the LP tanks can easily hold more gas or air than the HP130.

 

[Diverdown269]

Thanks for the info guys. Perrone, how can an LP hold more gass than an HP. seams physicly imposiable....

I am working my way into tech and am just trying to figure out what would be the best tanks. I'm not an air hog, I'm just thinking the more gass, the better. I want to do deep ship wrecks and caves, so I'm thinking HP 120 or 130's would be the best way to go.

I am also working on my assistant intructor cert, so having the extra gass would make a day with students easyer as well i assume. A single 120 or 130 should last me through their 3 dives a day.

 

[BoltSnap]

And in some places (like where I live) the LP tanks can easily hold more gas or air than the HP130.

Sorry, but how is that possible?

 

[scawt]

Ok. A low pressure 108 is suppose to only be filled to 2400 psi. But if you fill it up to 3600 psi, like you would a high pressure tank, you get more cubic feet.
Mathematically it is 108 cf divided by 2400 psi gives you 0.045. This is the magic number of cuft per psi. Now you multiply that by what the tank is actually (potentially) filled to (3600) and you get 162 cubic foot.
Are you suppose to do this? No
Do people do it? Yes
Do dive shops fill low pressure tanks to 3600? Depends on the shop.

Hope this helps

Scott

 

[Spg01]

If you put 3,000 psi into that low pressure 108 it will have 135 cu ft of gas. I have heard of cave divers doing it in Florida. If you search the tank forum you will probably find a few threads talking about it.

 

[T. Bix]

And in some places (like where I live) the LP tanks can easily hold more gas or air than the HP130.

My tech instructor said the same thing in passing and I haven't had the opportunity to ask him about it.... Please expand on this.

 

[BoltSnap]

Got it. That is scary.

 

[PerroneFord]

Thanks for the info guys. Perrone, how can an LP hold more gass than an HP. seams physicly imposiable....

Not at all...

I am working my way into tech and am just trying to figure out what would be the best tanks. I'm not an air hog, I'm just thinking the more gass, the better. I want to do deep ship wrecks and caves, so I'm thinking HP 120 or 130's would be the best way to go.

You'll note that cave divers rarely use HP tanks. Once you come to understand why that is, you'll have the answer to the first question.

Oh and by the way, the capacity of a LP tank assumes a fill to it's plus rating if 2640psi.