Tanks Upside down? why not

[captain]

I believe most commercial divers use the upside down mounting on their AL80 bailout cylinders because of ease in reaching the valve.

 

[captain]

The four tank black and silver Cousteau rig is an interesting set up. I inspected it at the Weeki Wachi Dive into History weekend last spring. The three left side tanks are the primary supply with one valve at the regulator, the forth cylnder on the right is the reserve with the valve at the hip. No redundant regulator post, or isolation between the three primary cylinders. This was all put together using mostly off the shelf stainless steel tubing and fittings and some modification to existing valves. Very little in the way of special pieces. Some day I may build a similar setup using three 40 cu/ft cylinders with one as the reserve.

 

[mike_s]

I think the basic reason is that the tank in flat on the bottom and easier to set down that way...


but no one metioned that if the tank was inverted and had any moisture in it, that without the 'dip tube' on the valve, that moisture would run into the first stage which might cause a 1st stage failure (to produce breathable air at depth). Just something else to consider.

 

[drbill]

Wow! those are interesting setups Luis, thanks for posting them. That Cousteau rig is unreal!

Not really... if I'm not mistaken it is the one used in a TV documentary I worked with them on. Wish I had one of my own!

 

[drbill]

but no one metioned that if the tank was inverted and had any moisture in it, that without the 'dip tube' on the valve, that moisture would run into the first stage which might cause a 1st stage failure (to produce breathable air at depth). Just something else to consider.

Good point, Mike. Another issue related to the 'dip tube' (which I call the 'debris tube') is that in the inverted position, particles inside the tank are more likely to fall into the tube and clog the valve itself, shutting off air supply. I've had this happen when I did a head-down descent a few years ago... resulting in NO air coming out of the tank valve period (to second stage, octopus or BCD). Doesn't happen often, but it DOES happen!

Hmmm... maybe when I shift to my inverted pony I should only breathe on it in an inverted position. Well, that might be easier when I do my feet first ascents in my new dry suit!

 

[Luis H]

Not really... if I'm not mistaken it is the one used in a TV documentary I worked with them on. Wish I had one of my own!

For more Cousteau pictures and information, please visit Ryan’s web site:
http://www.flashbackscuba.com/

Look under: museum
And then: “The World of Jacques Cousteau”

 

[Luis H]

Good point, Mike. Another issue related to the 'dip tube' (which I call the 'debris tube') is that in the inverted position, particles inside the tank are more likely to fall into the tube and clog the valve itself, shutting off air supply. I've had this happen when I did a head-down descent a few years ago... resulting in NO air coming out of the tank valve period (to second stage, octopus or BCD). Doesn't happen often, but it DOES happen!

Hmmm... maybe when I shift to my inverted pony I should only breathe on it in an inverted position. Well, that might be easier when I do my feet first ascents in my new dry suit!

That is what the “dip tube” is design to prevent from happening, but some are better designed than other.

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.

 

[The Anchor]

It seems to me that everyone is missing a fairly obvious reason to have the valve at the top. That tanks are rounded on the to and would therefore move through the watter easier. Admittedly, divers are generaly not moving at speed through the water, but given the increased density at depth, I for one want as streamline a profile as I can get. I would think that the base of the tank would create a large drag while swimming.

If you look at all the pics of upside down tank configurations, they all had some way to stream line the profile and most if not all used double round tanks.

For the record, I know that firemen use upside down tanks, but I believe they are double rounded as well.

 

[Luis H]

That is what the “dip tube” is design to prevent from happening, but some are better designed than other.

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.

I remember seeing a service bulletin that mentioned this, but I can't find it and more important I just saw, at one of my LDS, that brand new valves still come with the opening at the end of the dip tube. Therefore, I am not sure if that service bulletin is still the latest recommendation. I will look it more.

 

[Luis H]

It seems to me that everyone is missing a fairly obvious reason to have the valve at the top. That tanks are rounded on the to and would therefore move through the watter easier. Admittedly, divers are generaly not moving at speed through the water, but given the increased density at depth, I for one want as streamline a profile as I can get. I would think that the base of the tank would create a large drag while swimming.

If you look at all the pics of upside down tank configurations, they all had some way to stream line the profile and most if not all used double round tanks.

For the record, I know that firemen use upside down tanks, but I believe they are double rounded as well.

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.