Large tanks question

[cicopo]

Based on what I was taught when getting certified and in an ideal fill situation it should go like this. Aluminum tanks are supposed to be filled to 3000 PSI as the full pressure COLD. Compressed air is hot so they normally overfill a bit so that when things stabilize the tank will have the 3000 PSI. AL80's hold 80 cu ft of air, AL 100's hold 100 cu ft of air so in theory 20% more bottom time.
Steel tanks however can be filled to 3500 PSI (if I remember correctly) which was the primary reason for the different valve) so you have even more air in the same number of CU FT tank (a steel 80 would have more air than an AL 80 because of the extra pressure the tank can take, but I don't know how much by volume that would work out to but I don't think it would be as much as the AL 100 holds).

 

[1erCRU]

Scuba tanks are called by their nominal capacity and material. An AL80 has, when filled to designed pressure (3000psi), 77cu.ft. of gas and is made of aluminum. An HP120 PST (pressed steel tank) filled to design pressure (3442psi) has 120 cu.ft. (+-) of gas. etc etc.

DIN300 valves used to be the standard for HP tanks and were designed not to be compatable with the standard regulator yokes. Things changed and HP tanks were manufactured to accept a either a DIN 200 or a K valve or a combo valve. The orignal concern with HP tanks was that some older regulators were designed in the 2250 psi tank era and might not tolerate the higher pressures.

Aldora, as an example, supplies steel 100s & 120s which do not require a DIN regulator.

 

[DjDiverDan]

Personally, I like the DIN valve - it doesn't have the yoke around the valve stem of the tank, which has a tendency to whack me in the back of the head when I look up. The DIN Adaptor is small, cost me about $45.00 at LiesurePro, & I can switch back & forth from the Yoke to the DIN in about 3 minutes with a wrench on my Multi-Tool. You need to be sure to get the right one to fit your Regulator. Does anyone on the Island other than Aldora offer the HP Steel tanks? I really like the bouyancy characteristics of the Steel - I'm fat & need plenty of weight to get under, so the extra negative bouyancy of Steel Tanks (and the fact they don't get positively bouyant near the end of a dive) is nice.

 

[Invictys]

I can't see why I would want to dive with an AL100 over a Steel 120 unless I were really short and the 2 inches of tank height mattered to me. Steel 120 vs AL80 is still a no brainer in my opinion though I think a Steel HP100 seems best overall since its shorter, lighter, better buoyancy, and holds substantially more when filled to capacity. Even underfilled to 3000psi you still have 15% more air than an AL80

This info was pulled from the following site X-Series Steel SCUBA Tanks by Worthington Cylinders - Dive Gear Express and Aluminum SCUBA Tanks - Dive Gear Express and http://www.xsscuba.com/tank_alum_specs.html

STEEL

Cylinder // 2640 psi // 3000 psi// 3442 psi // Height(in.) // Weight (empty) //Buoyancy (full:empty)

---

X7 Steel 80 // 64 cu. ft.// 72 cu. ft.// 80 cu. ft.// 19.7 in// 28 lbs// - 9.0 lbs : - 3.0 lbs
X7 Steel 100// 80 cu. ft.// 89 cu. ft.// 100 cu. ft.// 24 in// 33 lbs// - 10.0 lbs : - 2.5 lbs
X7 Steel 120// 96 cu. ft.// 107 cu. ft.// 120 cu. ft.// 28 in// 38 lbs// - 11.0 lbs : - 2.0 lbs

ALUMINUM

Cylinder// 3000 psi// Height(in.)// Weight (empty)// Buoyancy (full:empty)

AL80// 77.4 cu. ft.// 26.1 in// 31.9 lbs// - 1.8 lbs : + 3.2 lbs
AL100 // 98.8 cu. ft.// 26.2 in.* // 41 lbs// -4.3 lbs : +1.9 lbs

*AL100 is 8 in. diameter not the standard 7.25 in. making it the same height as an AL80

 

[cicopo]

Based on those numbers the extra pressure in the Steel 80 (in ideal fills) only gets you 2.6 cu ft of air which is about a 4-5% increase tops.

 

[Invictys]

True, my comparison was the Steel 100 vs the AL80

But even with the Steel80 it's still 6 inches shorter and a few pounds lighter

 

[StuartT]

25% more gas with the al100 and 50% more gas with the steel 120 than an al80 unless my math is wrong

Okay, I already know the answer, but I'm asking for a friend...

What exactly are the differences...

There are AL80s and AL100s.... I'm figuring the AL100 has more air... how much more, how much more bottom time?

There are steel 120s.... I'm guessing these are the biggest most capacity available? More capacity then an AL100? How much more?

Let's say on an AL80 our hypothetical diver gets 40 minutes, what would you get with the AL100 and the Steel 120?

 

[Zman96]

When I use the AL100s I tend to average 65-70 minutes per dive depending on the depth of the dive. Of course my first dive of a trip it is usually about 10 minutes less due to excitement and getting gear comfortable again!

 

[Invictys]

Since the actual capacity of an Al80 is 77.4 cu. ft and AL100 is 98.8 it actually works out to 27.7% more with the AL100 and 55.0% more with the Steel 120 when both are compared to the AL80.

 

[loko2dive]

With the AL80 I get about 35-40 min bottom time, how much more time will the HP100 and HP119 give me ??
I'm trying to some research before buying my first two tanks. I'm looking into buying XS Scuba Worthington Cylinders HP Steel 3442 psi. Tanks, but can't decide if to get HP100 or HP119. Any one has anything to say about these tanks ?? Also anyone know the best place to order these tanks ??

Thanks