New Jersey Scuba Diving

Here are some dimensions and specifications for scuba cylinders. This is by no means an exhaustive list. These numbers should be taken as approximate since equivalent tanks from different manufacturers will differ slightly. The two most common models - the Catalina aluminum 80 and Luxfer aluminum 80 - are highlighted, along with my favorite, the OMS LP steel 85.

• Weight, full - this is what you will have to be able to lift, in and out of your car, around the dock, and up the boat ladder with all your other gear. Times two for doubles.
  
• Weight, empty - this is pretty much irrelevant
  
• Buoyancy, empty - this is what you need to weight yourself for, so that you can do a safe free stop at 20 feet at the end of your dive
  
• Buoyancy, full - this is what your BC needs to be able to support when you jump in the water, otherwise you are a "dirt dart" heading straight for the bottom and disaster

	Rated Size	Rated Pressure	Dimensions	Weight	Buoyancy +
height	diameter	empty	full	empty	full
cu.ft.	psi	inches	inches	lbs	lbs	lbs	lbs
Aluminum:
Luxfer 63	63.0	3000	21.9	7.25	26.9	31.7	2.5	-2.3
Catalina 80	77.4	3000	25.8	7.25	31.6	37.6	4.1	-1.7
Luxfer 80	77.4	3000	26.1	7.25	31.7	37.4	4.4	-1.4
"Super 80"	80.0	3000	22.9	8.00	35.0	40.9	2.2	-3.7
generic 100	100.0	3300	26.2	8.00	40.8	48.2	3.5	-3.9
LP Steel:
OMS* 66	66.0	2640	21.0	7.00	25.0	28.8	-1.7	-5.5
Faber 72	71.4	3000	20.5	6.84	29.0	34.4	-5.9	-11.3
OMS* 85	85.0	2640	26.0	7.00	31.0	37.7 1	0.0	-6.7
OMS* 98	98.0	2640	24.0	8.00	38.0	45.7	0.0	-7.7
PS** 104	104.0	2640	26.2	8.00	46.0	54.1	-2.5	-10.6
OMS* 108	108.0	2640	26.0	8.00	41.0	48.0	-1.0	-8.0
PS** 120	120.0	2640	33.0	8.00	54.0	63.5	0.0	-9.5
OMS* 121	121.0	2640	29.0	8.00	45.0	54.5	0.0	-9.5
OMS* 135	131.0	2640	30.7	8.00	47.0	58.1	0.8	-10.3
OMS* 71	71..0	3440	21.3	6.75	24.7	30.1	-1.4	-7.0
OMS* 80	80.0	3440	20.9	7.25	28.6	34.7	-1.7	-8.1
PS** 80	80.0	3500	19.8	7.25	27.0	31.5	-1.0	-5.5
OMS* 100	100.0	3440	25.4	7.25	34.3	41.9	-0.6	-8.4
PS** 100	100.0	3500	23.9	7.25	33.0	40.5	0.0	-7.5
OMS* 119	119.0	3440	24.2	8.00	38.9	47.9	0.2	-9.1
PS** 120	120.0	3500	29.0	7.25	38.0	49.0	1.0	-10.0
Aluminum
Catalina 13	13.2	3000	12.3	4.37	5.4	6.4	-0.4	-1.4
Luxfer 20	19.9	3000	21.9	4.38	8.2	9.5 2	0.1	-1.4
Catalina 30	30.0	3000	20.0	5.25	13.7	16.0	0.0	-2.3
Catalina 40	40.0	3000	24.9	5.25	15.7	18.7	1.9	-1.1
Steel
OMS* 46	46.0	2640	23.0	5.50	17.6	21.6 3	0.0	-4.0
OMS* 20	20.0	2640	19.5	3.90	7.5	9.0	-1.5	-3.0
Hmm ...
OMS* 85	97.0	3000	26.0	7.00	31.0	38.4	0.0	-7.4

¹ with valve, boot, and a good fill - 42 lbs HP Steel: ( DIN valve only )

² with valve & mounting bracket - 11 lbs

³ with valve, boot, and a good fill - 23 lbs

+ at rated pressure
* Faber** Pressed Steel

density of dry air = 0.076 lb / cu-ft

Weights and buoyancies that I would consider to be excessive are highlighted in red. In particular, the Faber 72 is ridiculously heavy for its size, and excessively negative, and aluminum 80s are far too buoyant when empty.

Notes on the hydro test

The hydro test requires a tank to pass certain dimensional criteria when filled to 5/3 of its rated pressure. For a low-pressure steel tank, this is 5/3 x 2400 = 4000 psi, which, for an OMS/Faber, is the manufacturer's rated pressure outside the United States. In other words, it is really no test at all, or, you basically can't fail hydro. ( You can still let it rust, though ! ) For an aluminum tank, this is 5/3 x 3000 = 5000 psi, and aluminum tanks fail quite commonly. For a high-pressure steel tank, hydro pressure is 5833 psi. Good luck.

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Thanks again to diver Art Greenberg for scrupulously checking these numbers ( even though he's still not quite satisfied with them. )