Question Picked up a pair of Faber LP95s, do I need to tweak my weighting for buoyancy?

[grf88]

Wow, what gas giant are you living on? LOL

Air actually weighs about 0.08lb/cf.'t

Just because an 80cuft tank sometimes feels like half a ton doesn't mean it does. He had the 12.4 correct but that is cu.ft. to the pound.

 

[inquis]

Wow, what gas giant are you living on? LOL

Air actually weighs about 0.08lb/cf.

LOL, units were backwards/upside down. 12.4 cuft per pound = 0.08 lb/cf

 

[inquis]

Well, I dive 17-18lbs now with HP100s. I’ll jump into a pool and see if I need to make any changes - or I can wait for my next ocean dive and see if I can get the boat to hand me extra weights

Lead requirements in a pool and ocean will be quite different. If 18 lbs works in the ocean, I'd suggest 13 lbs in a pool if you're lighter than about 190 lbs or 12 lbs if you're heavier. The adjustment goes as (your dry weight + 60 for gear & lead) * 0.024. Figure out what works in the pool and then add the adjustment back in for the next ocean trip.

 

[Tanks A Lot]

I checked several other places which agree with the +1.7 lb. (TBH, I've not found the Huron list to be very accurate.)

While the Huron list is good for estimates, it is indeed wrong in certain places.

As I mentioned before, I find the distinction by cubic feet, coupled with LP & HP silly to say the least for cylinder identification. As for the LP95 and HP100, it will be likely those ones from Faber:

Water Capacity (L)	Diameter (mm)	Length (mm)	Working Pressure (Bar)	Empty Weight (Kg)	Empty Buoyancy Seawater (Kg)	Full Buoyancy Seawater (Kg)	Real Weight Seawater (Kg)	Empty Buoyancy Freshwater (Kg)	Full Buoyancy Freshwater (Kg)	Real Weight Freshwater (Kg)	Standards	Comments	Other
15.0	203	605	184	16.9	0.77	-2.43	17.67	0.25	-2.95	17.15	DOT 3AA / TC3AAM	DOT 3AA: W.P.2640 PSI (INCLUDING 10% OVERFILLING)	TC3AAM,W.P. 184 BAR
11.9	184	615	244	17.6	-3.03	-6.4	14.57	-3.46	-6.83	14.14	DOT 3AA / TC3AAM	DOT 3AA: W.P.3495 PSI (INCLUDING 10% OVERFILLING)	TC3AAM,W.P. 244 BAR

Attached is a list, directly from Faber with exact numbers, except the column "Estimated US Sizes". This has been calculated and I have no way knowing which compressability factors and temperatures Faber used to calculate capacity. You may find slight rounding errors for cylinders of the US market, as the imperial numbers have been converted to their metric counterparts. It will be close enough though...

 

[inquis]

As for the LP95 and HP100, it will be likely those ones from Faber

I agree the LP95 (15 L) row is likely what the OP has. Buoyancy of +0.77 kg = +1.7 lb

I don't think the HP100 row you listed (11.9 L) is right as the working pressure is fairly different from the typical 3442 psi/237 bar found in the US. In the spreadsheet (thanks for that, BTW!), row 291 seems reasonable. Buoyancy of -0.27 kg = -0.6 lb.

 

[Tanks A Lot]

I agree the LP95 (15 L) row is likely what the OP has. Buoyancy of +0.77 kg = +1.7 lb

I don't think the HP100 row you listed (11.9 L) is right as the working pressure is fairly different from the typical 3442 psi/237 bar found in the US. In the spreadsheet (thanks for that, BTW!), row 291 seems reasonable. Buoyancy of -0.27 kg = -0.6 lb.

You are absolutely right! I must admit that the US system of classifying cylinders has eluded me since forever. Thanks for correcting me there.
For whoever is too lazy to open up the spreadsheet, this is what i should have posted before:

Water Capacity (L)	Diameter (mm)	Length (mm)	Working Pressure (Bar)	Empty Weight (Kg)	Empty Buoyancy Seawater (Kg)	Full Buoyancy Seawater (Kg)	Real Weight Seawater (Kg)	Empty Buoyancy Freshwater (Kg)	Full Buoyancy Freshwater (Kg)	Real Weight Freshwater (Kg)	Standards
12.9	184	645	237	15.6	-0.27	-3.81	15.33	-0.71	-4.26	14.89	DOT EXEMPTION

 

[lexvil]

I just can’t get my head around the kilowhatsits and litters but the LP 95 is a pig of a tank, heavy out of the water and floaty in the water. The nice thing is the get over filled often so they will pack a nice amount of air.

If you can do 18 lb in salt water with an HP 100 you’ll need 21 or so with the LP 95 to start, it’s all about displacement and the 95 displaces a lot more water than the 80 or 100 wether is fresh or salt.

 

[jellycatsdad]

I just can’t get my head around the kilowhatsits and litters but the LP 95 is a pig of a tank, heavy out of the water and floaty in the water. The nice thing is the get over filled often so they will pack a nice amount of air.

If you can do 18 lb in salt water with an HP 100 you’ll need 21 or so with the LP 95 to start, it’s all about displacement and the 95 displaces a lot more water than the 80 or 100 wether is fresh or salt.

Well, more air is a good thing despite my SAC improving from when I started diving(50-60psi/m) to now(32psi/m). But the buoyancy math with the LP95 is confusing. I shouldn’t have buoyancy issues with these vs. aluminum if I get the weighting down?

 

[Still Kicking]

Well, more air is a good thing despite my SAC improving from when I started diving(50-60psi/m) to now(32psi/m). But the buoyancy math with the LP95 is confusing. I shouldn’t have buoyancy issues with these vs. aluminum if I get the weighting down?

I have the philosophy "better to have it and not need it than to need it and not have it." Goes double for gas. Also, I consider diving part of my exercise regimen (ha ha!) and so a heavier tank makes for a more rigorous workout

The low pressure 95 has largely been surpassed by the HP100 as the go-to tank for most male divers (except in the narrow exception of "cave fills") but it's also a matter of "dive what you have." I wouldn't toss out a 95 and go and buy a 100 just because. I dove a 95 for a long time before I started accumulating high pressure tanks and I never noticed any issues with it.

 

[lexvil]

Well, more air is a good thing despite my SAC improving from when I started diving(50-60psi/m) to now(32psi/m). But the buoyancy math with the LP95 is confusing. I shouldn’t have buoyancy issues with these vs. aluminum if I get the weighting down?

You should be within 2 to 4 lbs between them I should think. You have them so do your low pressure weight checks and go from there.