Tanks Upside down? why not

[fdog]

Victor, here you go... a look at how these inverted cylinder threads always pan out:

A prior post on this very subject

All the best, James

 

[redacted]

I realize that it is not intuitively obvious, but a blunt rear creates more drag than a blunt leading edge.

Look a a tear drop shape. The front is rounded but relatively fat, the rear is always streamlined and pointy.

Also look at an airplane wing, the airplane body, a Navy submarine, etc. The shape of the rear is always finer and pointier the the bulbous fat front.


As side note, many cars are shaped to look fast to the human eye, not necessarily the same as low aerodynamic drag. The very early Saab were design with aerodynamics in mind, y a group of aircraft engineers.

And then there is a bullet!!! But I guess a little drag is necessary for stability.

 

[Luis H]

And then there is a bullet!!! But I guess a little drag is necessary for stability.

I don’t know much about bullets and all its design requirements. I do know it needs to work like a piston while it is accelerating on the barrel.

A major consideration is that the physics involved with very high speed objects in a compressible fluid (like air) are quite different. A supersonic object wants to be wedge shape, but even subsonic objects have related drag effects as the speeds get high enough. I think you can see it in the difference in shape for an M-16 bullet versus a slower bullet like a 38 caliber.

Again, I don’t know much about bullets (and aerodynamics is not my specialty either).
I don't want to high jack the thread either.

 

[Jimmer]

I don’t know much about bullets and all its design requirements. I do know it needs to work like a piston while it is accelerating on the barrel.

A major consideration is that the physics involved with very high speed objects in a compressible fluid (like air) are quite different. A supersonic object wants to be wedge shape, but even subsonic objects have related drag effects as the speeds get high enough. I think you can see it in the difference in shape for an M-16 bullet versus a slower bullet like a 38 caliber.

Again, I don’t know much about bullets (and aerodynamics is not my specialty either).
I don't want to high jack the thread either.

I would expect the bullets are shaped like that partially because it's easier to cast in that shape, easier to mount in the shell in that shape, fills the barrel better to be pushed by the expanding gases. And I could be wrong but I would think the rifling would stabilize the bullet moreso than a teardrop shape.

 

[mikerault]

Look at the shape of a modern nuclear submarine, blunt nosed and tapered (yes I know, but we don't want to get banned) This is also the shape of many large ocean creatures such as whales. This shape argues that having a blunt end into the current or direction of travel may be better for underwater than other shapes. Of course at the spoeed most divers swim (<1 kt) then it probably makes little or know difference.

Just my 2 cents worth.

Mike

 

[grazie42]

I wouldn´t dive manifolded doubles inverted because I know I would have trouble reaching the isolator (having tried it).
I won´t dive unmanifolded doubles...so...
There is also the custom hoses, valve-guards etc that makes it less appealing...

One reason firemen use inverted tanks is that they have no reason to reach for the valve once it´s turned on. The valves and 1st stage are the most vulnerable components and firemen enter buildings where "stuff" falls down, hence the need to protect the vital parts of the rig...

 

[truck1]

Don't firemen and toxic waste workers wear the tanks reg down? I believe my nephew told me. He's wears all that gear while analyzing dumps and waste sites.

Yes we firefighters wear our airpacks with the necks down.The regulators are usually on our shoulders although there are a few exceptions.BUT the big thing is we are not trying to set things up on a moving object like a boat.Ours are already together.Generally speaking they are either in the seat we ride in where all we have to do is put our arms thruogh the straps then lean foward and stand up or in a compartment in a bracket where we do basically the same thing.We are more likely to get hung up on something like a fallen ceiling or airducts etc then the average diver.Is there situations where a neck/reg down position is needed/warranted in scuba?More than likely but the average (key word average)diver does not really need it and the industry is not going to change for the minority.Heres the other thing.When you factor in weights of units,assuming a weight integrated bc, when I take off an airpack after a fire or other incident where it is needed, I am only removing about 25 pounds of gear.Most of the time someone is around to assist me or whoever.In diving we are slinging a 35 pound tank assuming a standard al 80,plus say 16 pounds of lead in the pockets,plus a regulator say 5 pounds,and your already up to 60 someodd pounds,not counting anything else you have attached.Then factor in a moving boat.Personally its a whole lot safer with the neck up especially if it drops.

 

[Tom Winters]

If mounting the tanks upside down works for you, go for it. Back in the '60's, it was not uncommon to see tanks mounted this way once single hose regulators became fairly common.
The drawback always was dropping the tank on the valve. Most likely, it wouldn't explode, but you'd pretty much have a ruined valve and maybe a cracked yoke fitting if the reg was still attached. When I started, I used a thick leather belt to hold the tank to me - carrying it involved stooping over and cupping the bottom of the tank so the twin hoses didn't strangle you - we looked like Igor the hunchback heading for the water. I was really pumped when I saw the first US Divers backpack.
There was a really cool Swedish Divator mini-triple tank 5000psi system that mounted the valves underneath. 5000psi just never caught on for lots of reasons, but it sure was a nice idea then.
Unless the tanks had the OMS valve protectors and I knew the diver, I'd be leery of letting someone use their tank upside-down on my boat. Just too many years of seeing the most unbelievably stupid things that divers are capable of doing.

 

[victor]

Victor, here you go... a look at how these inverted cylinder threads always pan out:

A prior post on this very subject

All the best, James

James I suspect you are right it is momentum and lethargy that will keep us using the second best solution rather than changing, even when we know better.

I have seen a number of incidents on dive boats where a rig has fallen off a bench, someone has set up there BC’ etc and forgotten to hook back the bungee.
Since tanks are sitting on their butts, when they fall over they, naturally, fall on their valves. In most cases someone managed to grab them before they hit the deck but in some the first stage was knocked loose and the sound of escaping air got everybody’s attention.

If the tank was valve down in the rack then, if they fell over, they would land on their butts and do no damage, except to the foot that was between them and the deck.
So I feel that the falling over argument is spurious.

It would only take a little ingenuity to resolve the problem when donning and doffing your rig on the back of a boat. The use of OMS valve protectors as Tom suggested would be an excellent option, not a bad idea no matter which way up you have your tank, see above.

Thanks Dr Bill and Luis H
Anyway I will pull all my valves and make sure the dip tube has been modified. I too mount my pony with the valve pointing down level with the bottom of my tank, and I often end up standing on my head trying to get a photo.

In many dip tubes the opening is at the end of the tube, which can still allow particles from falling on the opening. Granted the probability is low. This design of “dip tube” is supposed to be modified by pinching the end and drilling two holes perpendicular to the tube, near the end of the tube. The holes are drilled all the way through making four holes on the tube, near the end .

Dip tubes with holes on the side of the tube (as the modified version) are almost impossible to clog.

Well we will see maybe someone will come up with a better solution but the advice on dip tubes makes this thread well worth reading

 

[Luis H]

Anyway I will pull all my valves and make sure the dip tube has been modified. I too mount my pony with the valve pointing down level with the bottom of my tank, and I often end up standing on my head trying to get a photo.




Well we will see maybe someone will come up with a better solution but the advice on dip tubes makes this thread well worth reading

I am still looking for the service bulletin were I saw that. I thought that it was from Sherwood, but it might have been Scubapro. Scubapro valves did incorporate this feature at one time.

I have been looking at new valves, and it puzzles me why none of them incorporate this feature. Was it more trouble that necessary, considering the low probability of clogging? I don't know, but will look more into it.