Steel vs. Aluminum tanks

[maniago]

Bill, you know you can have the rusted tank tumbled and then washed with flash rust preventer (Global MFG comes to mind Oxy-Safe Rust Inhibitor - Gallon), right?

 

[Tigerman]

I used to dive with two HP120 steel tanks. Loved them. Could get 2-3 good dives out of one. Unfortunately, I no longer have either one in a functional state.

One failed its third hydro due to over expansion caused by hot fills at one shop (it was used strictly for shore diving). The other failed VIP due to rust from wet fills on dive boats (it was used almost strictly for boat dives).

Along with these two tanks I've had a neutral buoyancy Al 80 tank that had its first hydro in the 1970s. It is still in service and I bought a second one as well. Great tanks IMHO.

are those neutral bouyancy AL80s much different to handle (other than not going positive when empty) than the standard AL80s in "the real world"? They are a bit heavier due to the thicker walls are they not, but is it even noticeable?

 

[NAM001]

Most fresh water locations will use al tanks. Once you cross to the salt side you need the weight to counter the added bouyancy of salt water. Warm water or not it is the nature of the ocean beast. Now double whammy it with cold salt water needs the thicker wet suits and there you have it.

---------- Post added December 28th, 2013 at 09:46 PM ----------

Or they just have thier compressor shutoff set at less than 3500.

Yeah that's crap. All HP compressors can pump to at least 4000psi, and usually up to 5k. What is more likely is that they don't bank their pressure above 3000 because they are trying to eeeek the most service out of the thing. If they pumped you right off the compressor's dryer, you'd get what you want. But then again, most retail tank monkeys arent bright enough to know how to work a compressor, much less drive to work.

---------- Post added December 28th, 2013 at 09:54 PM ----------

Tiger
Please correct me if necessary

the only differece n hte 200 vs 300 din s the lenght of the threads. 200 and 300 will both work in the 200 female fut only the 300 male will work in the 300 female. The 200 adn 300 females are constructed differently so that the adaptor plug can not be put in the 300, and the 300 vents as the male is loosened from the female. All my regs and fill whips have 300 males on them and my tanks have 200combo females on them.

You can NOT fill a 230 bar DIN valve with a 300 bar DIN fill whip. I tried this only 2 weeks ago myself. It will not thread due to the longer center post...

---------- Post added December 28th, 2013 at 09:15 PM ----------


People around here have been known to use small 300 bar steel tanks for twin sets. Theire also frequently used by firefighters

 

[KD8NPB]

I don't know of any scuba tanks that are working pressure rated for DIN300 (4400psi), or anyone diving or selling them. DIN230(3442psi) convertables is what I have.

Luxfer 106 Composite Cylinder with Xs Scuba Din Valve, White at LeisurePro

I dive a lot of LP72s. I also have some HP100s, and an LP108.

 

[drbill]

Bill, you know you can have the rusted tank tumbled and then washed with flash rust preventer (Global MFG comes to mind Oxy-Safe Rust Inhibitor - Gallon), right?

My HP120 could not be tumbled... it was that rusty after one year. If it could have been saved, the owner of my local dive shop (a friend) would have done it.

---------- Post added December 29th, 2013 at 07:21 AM ----------

are those neutral bouyancy AL80s much different to handle (other than not going positive when empty) than the standard AL80s in "the real world"? They are a bit heavier due to the thicker walls are they not, but is it even noticeable?

Personally I don't find the neutral buoyancy tanks that different. They are heavier but since most of my "recent" (last decade or so) diving has been with the HP120s, they are lighter than that. I rarely dive a standard Al 80.

---------- Post added December 29th, 2013 at 07:22 AM ----------

Most fresh water locations will use al tanks. Once you cross to the salt side you need the weight to counter the added bouyancy of salt water. Warm water or not it is the nature of the ocean beast. Now double whammy it with cold salt water needs the thicker wet suits and there you have it.

I dive salt water in a 7mm wetsuit plus a 3-5mm hooded vest. The different between salt and fresh water in terms of buoyancy is, of course, noticeable but not that extreme. We dive aluminum and steel tanks both around here.

 

[tracydr]

Yeah that's crap. All HP compressors can pump to at least 4000psi, and usually up to 5k. What is more likely is that they don't bank their pressure above 3000 because they are trying to eeeek the most service out of the thing. If they pumped you right off the compressor's dryer, you'd get what you want. But then again, most retail tank monkeys arent bright enough to know how to work a compressor, much less drive to work.

I have the same problem. My LDS says they can't go over 3,000 psi.

 

[Ryan Nelson]

It's funny because after I had them filled yesterday he came out and claimed to have them at 3400. The tanks came back steaming hot and I argued that the pressure if it was at 3400 was reading high due to temp. Checked them after they cooled 3000 psi.

Is there a way to easily figure out the cubic feet relative to air pressure? For instance, if at 3500psi I had 100cf then at 3000psi how much air do I have?

Sent from my SCH-I545 using Tapatalk

 

[kwinter]

It's funny because after I had them filled yesterday he came out and claimed to have them at 3400. The tanks came back steaming hot and I argued that the pressure if it was at 3400 was reading high due to temp. Checked them after they cooled 3000 psi.

Is there a way to easily figure out the cubic feet relative to air pressure? For instance, if at 3500psi I had 100cf then at 3000psi how much air do I have?

Sent from my SCH-I545 using Tapatalk

1/7 less, or 85.7 cf. It's all relative. 3000/3500*100

And getting back to the original question of deciding between steel and aluminum, the only buoyancy issue you need to decide is with a full tank compared to how much lead you need. The change in buoyancy during the dive will be the same no matter what kind of tank you have. The only slight difference might be in how the buoyancy is lost at the top vs. the bottom of the tank.

 

[KD8NPB]

It's funny because after I had them filled yesterday he came out and claimed to have them at 3400. The tanks came back steaming hot and I argued that the pressure if it was at 3400 was reading high due to temp. Checked them after they cooled 3000 psi.

Is there a way to easily figure out the cubic feet relative to air pressure? For instance, if at 3500psi I had 100cf then at 3000psi how much air do I have?

Sent from my SCH-I545 using Tapatalk

Tell them to slow their fill rate and dunk your tanks...they should take about 10 min to fill, or longer.

If you have to, drop your tanks off, tell them to fill them VERY slowly, and you'll come back later. If you can hear valves whistling, the fill rate is too fast.

 

[Tigerman]

...
Tiger
Please correct me if necessary

the only differece n hte 200 vs 300 din s the lenght of the threads. 200 and 300 will both work in the 200 female fut only the 300 male will work in the 300 female. The 200 adn 300 females are constructed differently so that the adaptor plug can not be put in the 300, and the 300 vents as the male is loosened from the female. All my regs and fill whips have 300 males on them and my tanks have 200combo females on them.
...

Thats what I thought too and why I tried, but the 300 bar din whip has a longer post that goes into the tank valve - just barely too long to enter the thread?
I do see (because I want to research the option of getting my own compressor) that there is a "200/300 bar switch over" or whatever various manufacturers call it available which might be the solution to that problem..

..
Personally I don't find the neutral buoyancy tanks that different. They are heavier but since most of my "recent" (last decade or so) diving has been with the HP120s, they are lighter than that. I rarely dive a standard Al 80.
...

Cool. I ask most from curiosity really as Im very unlikely to run actross them using steel myself and I guess most dive ops will go for the standard al80s which I assume would be cheaper.