Scuba tank size and buoyancy calculator

[Hatul]

I"ll look at this more carefully when I get home, but the most important number is the empty buoyancy, usually given with valve, because that will determine how much lead to add/subtract when you change tanks. I would suggest you start with this number taken from tables and derive the others.

 

[henrik242]

I would suggest you start with this number taken from tables and derive the others.

Sounds like a bad idea, since we've already found errors in XS Scubas tables, and don't know how they calculate the bouyancy.

I've added a checkbox for the weight of valves, that might help. (And I added a checkbox for doubles while I was at it)

 

[Hatul]

For the HP80 there's a huge discrepancy that needs to be resolved. Both the XS Scuba and Divegearexpress
X-Series Steel SCUBA Tanks by Worthington Cylinders - Dive Gear Express

list the empty buoyancy as -3 lbs and the calculator gives -8.2 lbs with valve in seawater. I may just test my tank by dipping it in the pool.

Here are my measurements of full tanks, with valve and plastic dustcap of XS Scuba as weighed with a luggage scale.

tank, wt, buoyancy in freshwater all in lbs
HP100, 42.2, -10.8
HP80 39.2, -11.3

your calculator gives -11.6 lbs for the buoyancy of the 100 and -15 lbs for the 80.
table gives -10 and -9 lbs in salt water

Perhaps someone else can check their tanks with a luggage scale.

Did you ever get a reply from XS Scuba about their tables?

 

[henrik242]

Hi, thanks for weighing your tanks!

What's the empty weight of the tanks, as stamped on the tank neck?

XSscuba is still investigating, as I mentioned earlier in this thread.

 

[Hatul]

Hi, thanks for weighing your tanks!

What's the empty weight of the tanks, as stamped on the tank neck?

XSscuba is still investigating, as I mentioned earlier in this thread.

Hello Henrik,

It appears that the Worthington tanks do not have the weight stamped

http://www.scubaboard.com/forums/ta...worthington-steel-tank-markings-x7-100-a.html

I verified this by calling XS Scuba. The numbers they give me for empty wt in lbs no valve are:
33 for the HP100
30 for the HP80

Adam

 

[henrik242]

Hello Henrik,
I verified this by calling XS Scuba. The numbers they give me for empty wt in lbs no valve are:
33 for the HP100
30 for the HP80

Thanks again, Adam.

With a HP100 of 33 lbs, the calculator gives -11.5 when full in fresh water. A HP80 of 30lbs gives -12.7.

Allthough not spot on, it's not too far away from your measurements of -10.8 and -11.3.

It's almost impossible to get this exactly right, since there are several things that might influence this e.g.:

* The steel density might be slightly different from 490 lbs/cuft
* Buoyancy of tank net and tank foot
* The air pressure of your test tanks might not be exactly 3442 psi
* The weight of a valve is set to 2 lbs, but it can easily be from 1.5 to 2.5 lbs

After thinking a bit, I've set the valve weight to 1.5 lbs now. This makes the calculations closer to that of your tanks: -11.1 for HP100 and -12.3 for the HP80.

Also, I've added an option to view the actual calculations that are performed.