Steel tank volume question

[Scuba_Steve]

A "trig" function?
My mathematical education surely must be lacking!
Last time I checked, trigonometry dealt with the relationships of 3 angles and three sides of a triangle.

the K

Tell him to change his user name then. That's all he gave me to work with........besides, I liked conjunction-junction as a kid........schoolhouse rock man.

PS: Litres are so much less dumb than CF...... The euro's are so laughing right now, and deservedly so.

 

[Jason B]

That was easier than i though. Thanks for the help.

Cody, take your tanks rated volume and divide it by its service pressure to get your tanks baseline.

For a 100cu ft tank that would be 100/3442=.029 (now multiply by 100).

That gives you a baseline of 2.9

What does that mean? It means that every 100psi in your tank is 2.9cu ft of gas.

So 1000psi is 29 cu ft of gas.
2000psi is 58 cu ft of gas.
2900psi is 84 cu ft of gas.

You should know the baseline of your tank.


Oh, and (sinx = opp/hyp) is a trig function.

 

[Johnw...ski]

You are correct that the external dimensions of an AL80 and HP 100 are darned close.

In your case the upshot is that the aluminum tank has a wall thickness of about 1/2 inch. The steel cylinder is closer to 3/16. This difference adds up to considerable volume.

So while your tank pressures were probably very close there was more volume in yours.

For an HP 100 at 2900 PSI I get 84.25 Cubic Feet.

Pete

I agree Pete, if the 100cf is rated at 3442 psi. I calculated for 100cf at 3000 psi.

John

 

[xiSkiGuy]

I agree Pete, if the 100cf is rated at 3442 psi. I calculated for 100cf at 3000 psi.

John

To my knowledge, there is no such tank.

There are AL100s. They are 98.8cf at 3300psi...
There are lp98s (if you do funny OMS math, otherwise lp95). They are about 95cf at 2640psi...
There are HP100s. 100cf at 3442.

An FX-117 from Faber that is 117cf at 3442 that is underfilled to 3000psi gives you just short of 102cf. . .

 

[Jason B]

To my knowledge, there is no such tank.

No such tank as what? 100cu ft @ 3442psi?

Sure. PST E7-100 and the Worthington TWX-100Pro. Probably the most common 100cu ft tanks out there.


EDIT - never mind, I think I misunderstood your post.

 

[cadiver67]

Hi Trig,

You did have more air in your tank than your GF. How much who knows.

I did 3 dives at the Catalina Island park with my steel 100 tank and used the air fill van - the average fill was about 3200 - 3300 for me on that day. Never the full 3442 possible - so I never got the full 100 CF.

What I am wondering is did you dump some weight from your belt to compensate for the steel tank?

My wife and I just bought steel tanks frox XS Scuba I got a 100 and she got an 80.
My wife was able to dump about 7 lbs from her belt and I only dumped 4 lbs because I had a bigger tank.

The cool thing is that we used up our air pretty evenly for the first time (she always used to come up with a ton more air than me).

The bad thing is that we were sucking through our air way faster than we did with the aluminum 80s.

I finally realized on the last dive of the day that one of my legs was always finning and more tired than the other one. So I stopped and hovered for a minute and immediately rolled over on my back. I was way back heavy and was constantly finning to keep myself in position. If I had only realized that on the first dive of the day I could have rearranged my weights and had 2 more nice dives. But oh well.

My point - the steel tanks take a little getting used to and if your weighting was not balanced like mine wasn't - or if you were still had too much weight on your belt for the aluminum tanks you could have probably been burning throught you air quickly due to too much effort like we did.

I am going out again as soon as I can with the steel tanks - I think that once I get my weight distributed correctly that I will be exerting myself less and lasting much longer on the steel 100 - the best part is that I'm sure I will be even with my wife's air consumption.

cadiver67

 

[xiSkiGuy]

No such tank as what? 100cu ft @ 3442psi?

Sure. PST E7-100 and the Worthington TWX-100Pro. Probably the most common 100cu ft tanks out there.


EDIT - never mind, I think I misunderstood your post.

Yeah, I was refering to the 100cf @ 3000psi. But you're there now.

 

[Web Monkey]

It's also probable that although the dive shop was renting steel 100's, their fill equipment is only rated to 3000 PSI. If that's the case, then all they're really renting you is the added benefit of a steel tank, not more air. Remember, steel tanks also don't have the buoyancy changes as you assume air that the aluminum cylinders have.

FWIW, the buoyancy change is identical between steel and aluminum tanks.

100 Cubic feet of air weighs about 8 pounds. It doesn't matter if you have it in an aluminum tank, a steel tank or plastic bags.

An empty 100 Cu Ft tank will weigh about 8 pounds less than a full one, regardless of it's construction.

The steel tanks do have better (actually subjective-depends on the diver and equipment) buoyancy characteristics than aluminum, so you can take some weight off your belt.

Terry

 

[Lead_carrier]

Steel s-t-r-e-t-c-h-e-s more. Elasticity, you know.
.

It does what??? Come on RoatanMan, I hope this was just a shot at weird humor. If you really have 3000+ dives I hope you know better.

 

[douglasville diver]

I went through this myself, finally gave up on focousing on preasure and started thinking in volume.
LP or HP ? Don't matter 100 cf filled to3445 is still 100 cf.
I went with the worthington HP 130's, my LDS can give me a full 3445 psi,but alot of places can't, so it works out to around 117 cf @ 3000 psi and @ 2700 psi to be something like 104 cf.