Faber 108 Buoyancy Specs

[scubacalifornia]

Since I started diving last year, I've been using a PST steel 104 borrowed from a friend who now wants it back, so I'm faced with purchasing a tank. I was considering the PST E8-130, but the LDS called them today and delivery is quoted as Dec, 2004! I'm now considering the Faber 108, but am getting conflicting information on the buoyancy swing from full to empty.

Most of the tables I've come across on various websites show the 108 at -4.4 full and +3.4 empty. However, the LDS told me -8 full and neutral empty. They're actually selling the XS Scuba tank, which is made by Faber. And the XS Scuba website confirms the -8/neutral specification quoted by the LDS.

Can anyone help alleviate the confusion here? Is this tank really positively buoyant when empty? Also, if you are actually diving with a Faber 108 I would love your opinion. I'm mostly doing single tank shore dives off the So. Cal. coast, and have really come to like the PST 104 both for the extra capacity and that I'm only using 16lbs of lead with it (I weigh about 200 lbs).

Thanks!
Kevin

 

[The Wanderer]

I recently bought a new PST E8-119 and love it. My first tank. Use it with a BP/W.

You can probably find one of these if you look.

 

[scubacalifornia]

Since posting I contacted XS Scuba, who distributes the Faber 108 steel tank. I received the following reply from their product development person backing up their specification. Put on your math hat folks. I would still like to hear from anyone diving the Faber 108.

Using Archimedes principle, buoyancy is equal to the weight of the displaced water minus the weight of the cylinder.

The internal volume of the cylinder is 108 / 2640 * 14.7 = 0.6 cu ft

The cylinder is made of 41.4 lb of steel, (which has a density of 490 lb/cu ft). The steel therefore has a volume of 41.4 / 490 = 0.08 cu ft, so the total volume is 0.6 + 0.08 = 0.68 cu ft.

The density of salt water is 64 lb/cu ft, giving 0.68 x 64 = 43.5 lb

Air has a density of 0.075 lb/cu ft.
The air in a full cylinder weighs 0.075 x 108 cu ft = 8.1 lb.

The cylinder when empty has a buoyancy of 43.5 lb - 41.4 lb = 2.1 lb The cylinder when full has a buoyancy of 43.5 lb - 41.4 lb - 8.1 lb = -5.9 lb

These figures exclude the valve. When the buoyancy is adjusted for the added density of the valve the "rounded off" buoyancy is:

Empty = Neutral
Full = Negative 8 lbs.

Mike Piantoni
Product Development
XS Scuba