Two small steel tanks from 1970. Baby dubs, need help...

[lowviz]

I very recently put together a set of baby dubs using two cylinders that are very well-sized for my advancing age. The goal was to get a set that was perfectly balanced, could use my existing dual reg sets without modification, and didn't take a half-track to move. Did not go so well...

Long story short, the cylinders were not the angels from above, but the daughters from below. Overall size and weight seemed good but the roll was brutal.

Stepping back:
I hold current VIP and O2 cleaning certs (tanks, valves, manifolds). So I took the damned set apart in frustration and got the specifics for those who know more:

Dacor Tank:
DOT- 3AA2250 8(CL) 70+PST
My measured data:
Tank alone dry weighs 22.8# It is 19 1/2 " in overall length. Filled with room temp water to the bottom of neck threads it then weighs 42.0#.
Derived:
42.0# -22.8# = 19.2# of water.
19.2 pounds of water is about 8.7 liters.


Voit Tank:
DOT-3AA2250 2 (diamond with 'N' in middle) 70+ (Capital A with a line through the center) [I know what each means, but trying to remain overly descriptive for those who don't]
4 M 16336
Measured:
Tank alone (dry) weighs 21.1# it is 18 15/16" long overall.
Filled with water it weighs 39.5#.
Derived:
39.5#-21.1# = 18.4# of water.
18.4# of water is about 8.35 liters.


So, I have two rather similar tanks of about 1/2" off in length and about 0.35 liters off in volume.

How were these tanks advertised originally?

Anybody willing to sell a mate to either at a reasonable price? I really am trying to get a set of baby dubs...

 

[runsongas]

the water capacity puts them to be lp53s, but usually those are 1980 psi

 

[MichaelMc]

Go with AL40 doubles??

The tricky bit, for 8.5" c-t-c, is the bands. I have 5.5" diam 8.5" c-t-c on order from DiveRightInScuba, apparently Faber bands. And DiveRightIn claims they are 8.5" c-t-c. So in a week or so I can report how that source worked.

Diving AL40 doubles as independents (with bands that were off from 8.5") was nice. No drastic roll, maybe even none, but it was a bit ago, so my recollection is fuzzy. LP50 doubles is a later step, where roll may be an issue.

On around 6" c-t-c:
- Australia has the same necks and burst disk rules as the US.
Scuba Diving Valves and Manifolds from The Scuba Doctor Dive Shop - The Scuba Doctor Dive Shop
- They have 5.9" c-t-c isolation manifolds from San-o-sub, at The Scuba Doctor.
San-o-Sub Dual Outlet 232 Bar Isolation Manifold - The Scuba Doctor Dive Shop
More to follow eventually in Getting European 6.3" c-t-c isolator bars on U.S. tanks, where I posted a longer update. Any suggestions are welcome from our Ausi members. Maybe over there.

 

[AfterDark]

Those sound like a set someone put together not originally mated.
I've got a set of LP50's I use as IDs. No roll but empty it takes 12 pounds to make them neutral! Nice light set but the amount of lead needed brings me back to LP72 IDs weight. I think like @MichaelMc posted 2 40s maybe the way to go. I was looking at 2 LP63 AL tanks they are only 1.3lbs buoyant when empty. Might be time for me to think about selling some tanks.

 

[lowviz]

the water capacity puts them to be lp53s, but usually those are 1980 psi

You got me started, I finally got the math right (I think).

How about this:

Dacor 8.7 liters is 0.307 cuft. 2250/14.7 = 153 ATM 153 x 0.307 = 47.0 total cuft of compressed gas.
Both of these tanks were rated "+" at birth, so add 10% 47 + 4.7 = 51.7 cuft. Then adding the the unusable 0.307 internal volume at 1 atmosphere: 51.7 + 0.3 = 52 cubic feet !! I am aware of old LP52/53s. I think I have one.

Voit 8.35 liters is 0.295 cuft. 2250/14.7 = 153 ATM 153 x 0.295 = 45.2 total cuft of compressed gas.
10% correction: 45.2 + 4.52 = 49.7 cuft. Add the internal volume of 0.295 cuft and you get 50 cubic feet !!

So, bottom line, don't bother trying to pair up a 50 with a 52/53 (doh)

Anybody have EITHER a 50 or a 52/53 for sale? Insides of both of my existing tanks are pristine. So I'd be a bit picky about the interior...

 

[W W Meixner]

You got me started, I finally got the math right (I think).

How about this:

Dacor 8.7 liters is 0.307 cuft. 2250/14.7 = 153 ATM 153 x 0.307 = 47.0 total cuft of compressed gas.
Both of these tanks were rated "+" at birth, so add 10% 47 + 4.7 = 51.7 cuft. Then adding the the unusable 0.307 internal volume at 1 atmosphere: 51.7 + 0.3 = 52 cubic feet !! I am aware of old LP52/53s. I think I have one.

Voit 8.35 liters is 0.295 cuft. 2250/14.7 = 153 ATM 153 x 0.295 = 45.2 total cuft of compressed gas.
10% correction: 45.2 + 4.52 = 49.7 cuft. Add the internal volume of 0.295 cuft and you get 50 cubic feet !!

So, bottom line, don't bother trying to pair up a 50 with a 52/53 (doh)

Anybody have EITHER a 50 or a 52/53 for sale? Insides of both of my existing tanks are pristine. So I'd be a bit picky about the interior...

LV...

Late to the picnic...but...as has already been mentioned...put together a set of 3AL 40 doubles...or LP steel 50's...

Contact DGX (Dive Gear Express)...cylinders/bands/manifolds...new...inexpensive if you select the 3AL version...and you know what you have...

with what you currently have on your shop bench...you're trying to build a spork...it's a poor spoon...as well as a poor fork...

DIR...

Warren...

 

[lowviz]

Late to the picnic...but...as has already been mentioned...put together a set of 3AL 40 doubles...or LP steel 50's...

Huh?

Those are two VERY different beasts. Matched double 50's or matched double 52/53's are the exact same thing to me. Double AL 40's are way different.

with what you currently have on your shop bench...you're trying to build a spork...it's a poor spoon...as well as a poor fork...

Not exactly. Following the proven path:

Do something (that seems to make sense) and see how it works.
Analyze
Do something better.
Analyze
Repeat until stability is reached.

I had the wonky 50 52 set in the water with an instructor watching and trimming me out. I know exactly how much lead it takes to sink that set in thermals and a drysuit. A bit wonky, I'll admit, but most enlightening. Definitely not my tank/cylinder choice for a drysuit, BUT they fill a huge gap when it comes to balancing a rig. I dive both dry and wet, depending. One should be able to pick and choose among a few known and proven options to quickly put together a diveable, properly weighted, and balanced rig.

More than a few people and an agency or two instruct one to get a stable, properly weighted, and balanced rig and then leave it the 'F' alone. Nice, but I'm a local diver who experiences four seasons. Everything from ice to stinking hot humid miserable conditions. It is not uncommon for me to hike a bit to a 'secret' hole in a local creek/river. One solution does not fit all dive situations.

I believe that dual steel 50's (or 52/53's) would fill a valuable niche in my options for balancing a rig.

@MichaelMc: AL60's. Most interesting. They may become a topic of a future thread...


Postscript: Did anyone ever notice that all this would be so much simpler if the manufacturers would just state internal volume, weight, overall dimensions, and working pressure?

-somebody should invent that. <wink>

 

[abnfrog]

right on lowviz you actually understand .....not parrot what you hear that's the difference with an experienced diver vs a reader

 

[W W Meixner]

Huh?

Those are two VERY different beasts. Matched double 50's or matched double 52/53's are the exact same thing to me. Double AL 40's are way different.

Not exactly. Following the proven path:

Do something (that seems to make sense) and see how it works.
Analyze
Do something better.
Analyze
Repeat until stability is reached.

I had the wonky 50 52 set in the water with an instructor watching and trimming me out. I know exactly how much lead it takes to sink that set in thermals and a drysuit. A bit wonky, I'll admit, but most enlightening. Definitely not my tank/cylinder choice for a drysuit, BUT they fill a huge gap when it comes to balancing a rig. I dive both dry and wet, depending. One should be able to pick and choose among a few known and proven options to quickly put together a diveable, properly weighted, and balanced rig.

More than a few people and an agency or two instruct one to get a stable, properly weighted, and balanced rig and then leave it the 'F' alone. Nice, but I'm a local diver who experiences four seasons. Everything from ice to stinking hot humid miserable conditions. It is not uncommon for me to hike a bit to a 'secret' hole in a local creek/river. One solution does not fit all dive situations.

I believe that dual steel 50's (or 52/53's) would fill a valuable niche in my options for balancing a rig.

@MichaelMc: AL60's. Most interesting. They may become a topic of a future thread...


Postscript: Did anyone ever notice that all this would be so much simpler if the manufacturers would just state internal volume, weight, overall dimensions, and working pressure?

-somebody should invent that. <wink>

LV...

What you have is not matched...there-in lies the problem...or as you so aptly put it...''wonky''...if the cylinders were the same size dimension/wall thickness and had the same ideal gas capacity...you wouldn't be spending time balancing...

Further...once you've balanced your doubles full and your dive has commenced...you cannot maintain ''balance''...as the weight of each cylinder will change differently as they drain...because each cylinders' characteristics are different...the difference may be small...but it will be a difference...

When maintaining balance with sidemount cylinders...you're switching between seconds...so each cylinder drains equally...or reasonably so...

You need to find a cylinder to ''match'' either one of your existing cylinders...after which time...your balancing problem solves itself...

I've dove doubles for years...double HP steel 100's/double HP steel 80's...nothing to balance...ever...

One other thing to consider is that your existing BCD/wing...may not be filling and exhausting evenly...leaving one side with more air than the opposite side...gets you lop-sided real quick...

Post some photos when you're up and running...

Good Luck with your project...

W...

 

[lowviz]

What you have is not matched...there-in lies the problem...or as you so aptly put it...''wonky''...if the cylinders were the same size dimension/wall thickness and had the same ideal gas capacity...you wouldn't be spending time balancing...

OK, totally agree with that. But I believe that you missed something in what I said above. That set is already broken down and cleaned awaiting a perfect match (one more of either tank) for the rebuild. I have plans for that set when it all comes together...

I alone put those two tanks together on an isolation manifold with the question in mind, "Would this work?" At first glance, it seemed like it should. But it didn't go so well. Not dangerous, just not as well as I imagined that it could have. If it did work, I'd be happily diving them without a second thought. It didn't, we pursued why, and all learned something that works IRL.

It is all about exploring the "Why?" in real life. Well, now I know. Didn't take too many posts for me to get this far along either.

All: Thanks for your posts. I much enjoyed both the 'thinking' and the 'IRL testing' stages of this problem.