How much air does an LP85 hold at 2400 PSI?

[NAM001]

Am I confused? I thought you just multiply water capacity in liters by measured pressure in bar to get the gas volume in liters?

It is what you just said. liters * bar to et total liters of gas in tank. the point i think is that not all tanks are equal,,,, like the S80 and the C80. both 80's but one is like 12 ltrs and the other is like 10 or 11 liters. tank factor will reflect the difference.

 

[NAM001]

It's not like it's hard to multiply volume with the service pressure and figure out the amount of gas you'll have in a full tank though.
In fact, it's so easy you could train a monkey to do it with a calculator (which we all have in our phones) in a few minutes.
It also makes for really simple calculations during the dive.
Of course you can learn to do the same calculations with imperial units, but it's not as dead simple as metric.
Different tank pressures also tell us a lot about how much extra weight we'll need to bring on a dive.
A 10L 300 bar tank will need less lead than a 12L 232 bar tank because it's heavier in the water, although because of how gas compresses at higher pressures they will hold roughly the same amount of gas when filled to their service pressure.

thats part of hte problem i America. no one sells tanks as anything other than xxx cf , psi and material. al80 ,,, hp steel 100 etc. you will probably never see in a shop a tank labeled as a 13L 200 bar tank only as a AL S80.

 

[NAM001]

Wow. Ok well then I guess I’ll start telling them I have an LP76 and save some money since it seems the tank size can’t actually be determined.

I wouols suspect tha if the tank was marked other than an increment of 5 then it is probalby accurate. so if you have an lp76 adn it has a service pressure of 2400 then you multiply the 76 by I think 28.5 to convert form cu ft to liters and then divide that by the bar of the tank. for a 2400 tank that is about 163

76 x 28.5 is 2166 ltrs then ltrs / bar 2166 / 163 equals 13.2 liters water volumn. you have a 13 liter tank.

ifyouwant to do this iperial then 2400 / 76 and that is 31.6 pai per cuft. if they put 2000 psi in the tank to top it off then you bought 2000 / 31.6 cu ft.

 

[NAM001]

I recently weighed my twinset before and after filling. Here is the data I collected:

Before filling:

83.9 lbs @ 1150 PSI

After filling:

90.9 lbs @ 3550 PSI

That 3550 PSI was the reading 45 minutes later after entering the water at Ginnie Springs so the tanks had a chance to cool down a bit. Immediately after filling it was more like 3750.

I tried computing the tank sizes from this data but got some wild numbers that can't be correct. Have a crack at it if you would like to help me 100% determine what kind of tanks I have.

I will keep measuring my tanks before and after filling and post more data here as I collect it. I am using a digital bathroom scale and balancing the twinset on it the best I can on flat ground.

you filled 7# and got 2400 psi thats 342 psi for pound of gas. full tank is 3550 so you have 10.3 pounds of gas in the tank air is 8# per 100 cuft so

10.3 / 8 = 1.29 units of 100 cuft you have a tank with 129 cuft in it.

 

[Lorenzoid]

then you have the problem when you have a 13L/184 or a 13l/160 still the same complaint just a bit easier in math to use it.

So the Europeans sort of have what we would call HP and LP versions of a 13L tank? And being rule-abiding, I am guessing they don’t make a habit of filling tanks beyond their service pressure.

 

[Storker]

the Europeans sort of have what we would call HP and LP versions of a 13L tank?

Almost, but not quite.

The most common tank sizes - at least around here - are 7, 8.5, 10, 12, 15 and 18L. Fill pressures are 200, 232 and 300 bar. 200 bar is getting obsolete, 232 bar is rather popular since it provides a good balance between capacity and weight - and since compressibility still isn't much of an issue if you PP blend - and 300 bar tanks are preferred by those who appreciate a slightly more negatively buoyant tank.

Typical rec twinsets are D7x300 or D8.5x232, but I've seen D4 and D6 as well
Typical rec singles are 10, 12 or 15L, in 200, 232 or 300 bar (except 15x300, which is a true beast to schlep)
The typical tech twinset is D12x232. D15 and D18 are only for those with extreme gas reserve requirements, and quite a few of those are switching to rebreathers nowadays.

And it's generally steel. Al tanks are almost only used as ponies or stages due to them being largely neutrally buoyant (plus a little, minus a little, depending on how full or empty they are).

 

[NAM001]

So the Europeans sort of have what we would call HP and LP versions of a 13L tank? And being rule-abiding, I am guessing they don’t make a habit of filling tanks beyond their service pressure.

overfilling is not an issue in this. If I have an al 80, you dont know what tank I have because it comes in a 10 and 12 liter version (C80 or S80 and its not even an 80 to boot). The Europeans have say a 15ltr/232 ( made up tank) and with that marking there is no doubt what you have. by those 2 numbers you now the volumn. working pressure and capacity. the over fill is just a ratio adjustment to the capacity due to PSI change. Just looking at those numbers i can say one has +/- 200 surface minutes of breathing and still not fall below say 500 psi or so. The european markings are much more functional for those calculations. imperial is comfortable to americans to use but but when you say you again have an 80 cuft AL tank you dont really know what you have. tank factors are really easy to do in metric.

Another example is the lp121 by oms .... inverse to the S80 that tank has 125 in it adn not 121 cu ft.

 

[Storker]

The Europeans have say a 15ltr/232 ( made up tank)

We absolutely do. Nothing made up there.

Perhaps the most popular single around here is the 12x232. I once had a 15x200, but these days I use 10x300 because that allows me to carry some 4-5kg less on my belt (a couple kilos less compared to a 12). They have slightly higher nominal capacity, but nearly exactly the same real capacity (just a smidgen less than 100 of your cubic feet) . If you need more gas than that, the most common alternatives are D8.5x232, 12x300 or 15x232.

In warmer waters, I've typically used 12x200s. Most people use less gas while diving wet, and I guess those dive centers don't see much point in scrapping a bunch of perfectly usable tanks. Steels, when properly maintained, can last for decades.

There are quite a few who prefer a small twinset over a single for balance and comfort. I prefer singles, because it's easier to stow an extra single in my boat than having to go to shore for a refill during my SI.

 

[NAM001]

We absolutely do. Nothing made up there.

Perhaps the most popular single around here is the 12x232. I use 10x300. They have slightly higher nominal capacity, but nearly exactly the same real capacity (just a smidgen less than 100 of your cubic feet) . If you need more gas than that, the most common alternatives are D8.5x232, 12x300 or 15x232. There are quite a few who prefer a small twinset over a single for balance and comfort. I prefer singles, because it's easier to stow an extra single in my boat than having to go to shore for a refill during my SI.

Thanks for that. I was trying to emphasize the format of the tank designation knowing only about US tanks, and was trying to avoid someone saying that there is no such tank and going off topic. just the 12/300 by its self tells the whole story. If when we in the US when buying a AL S80 knew we were buying a 77/3000 it would be easy for us also. There is a lot that is so much easier to do in metric. I often wish compuers would display both imperial and perhaps metric on an alternate screen. Working depth in bar for math is so much easier.

 

[NAM001]

Almost, but not quite.

The most common tank sizes - at least around here - are 7, 8.5, 10, 12, 15 and 18L. Fill pressures are 200, 232 and 300 bar. 200 bar is getting obsolete, 232 bar is rather popular since it provides a good balance between capacity and weight - and since compressibility still isn't much of an issue if you PP blend - and 300 bar tanks are preferred by those who appreciate a slightly more negatively buoyant tank.

Typical rec twinsets are D7x300 or D8.5x232, but I've seen D4 and D6 as well
Typical rec singles are 10, 12 or 15L, in 200, 232 or 300 bar (except 15x300, which is a true beast to schlep)
The typical tech twinset is D12x232. D15 and D18 are only for those with extreme gas reserve requirements, and quite a few of those are switching to rebreathers nowadays.

And it's generally steel. Al tanks are almost only used as ponies or stages due to them being largely neutrally buoyant (plus a little, minus a little, depending on how full or empty they are).

Let me ask why most tanks are steel. is that because selected thermal protection makes steel the most practical. In the states or carribean it is AL that rules the waves but we need little if any thermal protection depending on the area. Ignoring the cave divers,,,I would guess that our north east and west divers use a lot of steel. Lots of dry suits.