How much air does an LP85 hold at 2400 PSI?

[Storker]

Let me ask why most tanks are steel. is that because selected thermal protection makes steel the most practical

I don't know, but that seems like a good guess to me.

 

[happy-diver]

and lots of pumping 232 to 260 in wetsuits to depth

 

[Eksilbergenseren]

Let me ask why most tanks are steel. is that because selected thermal protection makes steel the most practical.

Yes that is correct. There is probably a long list of pros and cons of alu vs steel, but there is definately a shift towards steel with lower water temperature.

In warm water you may be neutral or even negative without the tank. A negative tank will be unpractical and potentially dangerous. It will badly affect your trim, and also make you unneccesarrily negative. Alu-tanks tanks are therefore often the smart alternative diving with a 3 mm suite or less.

Diving in Norway we may use 7 mm wetsuites with another 5 or 7 mm on the torso, or more commonly a dry suite with a thick undersuite. You may need 10 to 15 kilos or even more weight to be able to submerge.
Steel tanks will give you two benefits. The negative bouyancy of the tank will reduce the neccesary weight in your BCD or belt. (Moving weight from belt to tank.)
A high pressure tank is also smaller. This reduced the total bouyancy, and thus the necessary wight. (Reducing the total weight of diver with equipment.) Having 30-40 kg of equipment reducing a couple of kgs really makew a difference on land.

For stage tanks, that you may clip on or of, you will want a tank as close to neutral as possible.

 

[Bob DBF]

In warm water you may be neutral or even negative without the tank. A negative tank will be unpractical and potentially dangerous. It will badly affect your trim, and also make you unneccesarrily negative. Alu-tanks tanks are therefore often the smart alternative diving with a 3 mm suite or less.

Sounds good, but a bit after the fact. When the AL 80 came out the big tank at the time was an old steel 72. The rental fleets were shifted to the larger tank with less maintainance, it was especially advantageous to warm water shops in the Caribbean where corrosion is a major concern. Larger steel tanks came out at a much later date in the Americas.

With better filtered compressors, divers not emptying tanks underwater, better maintainance procedures, and diver demand, larger steel tanks are now available in warm water locations.

Now there are numerous tanks to choose from, and at this point one can choose the proper tank upon whatever criteria one decides to be relevent.


Bob

 

[CaveSloth]

OK, got some new data today. Also, I bought what I think is a more accurate scale. I am using this scale to weigh the tanks before and after a dive:

https://smile.amazon.com/gp/product/B07P7Y6XF1/ref=ppx_yo_dt_b_asin_title_o04_s01?ie=UTF8&psc=1

For my twinset LP85s:

Before: 92.4 lbs at 3700 PSI
After: 86 lbs at 2300 PSI

I calculate this means that each of my tanks holds 74.5 cf of EAN32 at the standard LP85 working pressure of 2640 PSI.

For fun, I recorded data for my girlfriend's AL80 tank:

Before: 39.2 lbs at 3100 PSI
After: 35 lbs at 900 PSI

I calculate that this means that her tanks contain 70.7 cf of EAN32 at their working pressure of 3000 PSI.

Why are all 3 of our tanks deficient in their capacity???!!!?!?!?!?!? What am I doing wrong????

 

[Bob DBF]

The 85's are driving me nuts as well, it's like one tank is closed, as I mentioned before.

The AL 80 could be within the boundaries of instrument error as I was thinking on electronic paper below.

The scale needs to be as accurate as what you are measuring, a cuft of air is 0.08#. 7 cuft is only 0.56# on the scale. The SPG reading is only 38.86# for a cuft of air. 7 cuft is only 272# on the SPG.

I couldn't get a spec on SPGs, but for gauges that are not submersible, which I would trust to be more accurate due to their sheltered lives, are plus or minus 2.5 percent. This could mean a 150# error, and I've seen bigger errors on SPGs. 150# on the SPG is almost 4 cuft.

If the scale is off 0.25# (yours only measures in 0.2# incraments) and the SPG off 131#, that would lose 7cuft of air.



Bob
Still thinking

 

[Eric Sedletzky]

The thing that is confusing is that an LP85 does not contain 85 CF of gas at its rated pressure, but only when filled to 10% over its rated pressure. The + sign should not exist and an LP85 without a + sign should be called an LP77.

I agree

 

[CaveSloth]

The 85's are driving me nuts as well, it's like one tank is closed, as I mentioned before.

I did an experiment to make sure the isolator is functioning properly. I hooked my gf's SPG to one post and mine to the other and closed the isolator. Held down the purge on one regulator and saw that it did not effect the SPG on the other post. Then opened the isolator and saw the other SPG drop. Then repeated the test on the other side. So, the isolator is working properly.

 

[CaveSloth]

Once this weekend is over and we are done diving I am going to empty these tanks of air all the way and weigh their sorry butts.

 

[Sidemount_Ben]

Now to throw another monkey in the fire... According to Faber/Blue Steel. The LP85 actually has only a capacity of 81.1 Cuft of gas when filled to the rated pressure. SO when it is filled to only 2400psi it has only 73.72 cuft in them. kind of makes me question the whole ordeal on FALSE advertisement and misrepresentation.