Equalizing tank pressure at depth

[JonKranhouse]

TraumaDiver,

Check out this earlier patent, applied for in 1988, issued in 1989.

Just because there's an earlier patent doesn't mean that your idea wouldn't have good application in some situations. But not really practicable for an industry-wide change. Of course the devil is in the details (i.e. how to reduce water intrusion).

The recreational dive industry could learn much from the best practices developed in commercial and military dive cultures. I'm not suggesting a return to the days of doing push-ups with tanks / weight belts. And it takes a US Navy diver TWENTY YEARS to earn the "Master Diver" rank. But there is much more that can be put between divers' ears that will keep them safer and more comfortable, which increases enjoyment, and keeps people diving longer. Most instructors trained in the last 10 years don't know what they don't know.

Innovation only comes from people who seek to improve the status quo. And most people fear change. So don't buckle under to nay sayers.

 

[thanksforallthefish]

Personally I can see a problem in not introducing water into the transfer, though I am sure this could be overcome.

As to being attached to a diver that rockets to the surface etc ... what if they have your occy and do the same holding on to it? ... how about a quick disconnect system

I am no expert on regulators, but have seen a HP hose blow underwater and let me assure you there is a substantial ammount of air coming out very quickly, maybe it would take 5 mins to transfer maybe just ask a service tech.

There are some half full / half empty glass people here as well as some who's glass has never had anything in it.

Traumadiver ... dont let the naysayers get you down

 

[Notso_Ken]

I understand that there may be an issue with over-pressurization of your tank ....QUOTE]

How would you take 2 tanks low on air (1 critically) and end up with over-pressurization? They are going to equalize in between the 2 pressures. You won't have low pressure air flow to a higher pressure area.


Ken

 

[Peter Guy]

Reg B -- in fact, "Emergency Air Reserve" (i.e. Rock Bottom) IS typically 500 PSI for most of my dives -- at least at some point!

Example -- Typical Molokini dive -- AL 80 -- drop to 100 ft to look at "X" (last time was a flame wrasse) -- EAR at 100' is 1500PSI; but by 2000PSI I've gone up to 60 ft -- EAR at that point is around 1000PSI; but by the time I'm at 1200PSI I'm up around 30 ft -- EAR now is 500PSI -- and I'm able to play nice by the Dive Op's rules and be "Back on the Boat with 500PSI" (more or less).

Don't forget, EAR is NOT a static number during the dive -- it is the amount of gas you need to get you and your buddy safely to the surface from where you ARE -- not where you may have been.

 

[Reg Braithwaite]

Reg B -- in fact, "Emergency Air Reserve" (i.e. Rock Bottom) IS typically 500 PSI for most of my dives -- at least at some point!

Example -- Typical Molokini dive -- AL 80 -- drop to 100 ft to look at "X" (last time was a flame wrasse) -- EAR at 100' is 1500PSI; but by 2000PSI I've gone up to 60 ft -- EAR at that point is around 1000PSI; but by the time I'm at 1200PSI I'm up around 30 ft -- EAR now is 500PSI -- and I'm able to play nice by the Dive Op's rules and be "Back on the Boat with 500PSI" (more or less).

Don't forget, EAR is NOT a static number during the dive -- it is the amount of gas you need to get you and your buddy safely to the surface from where you ARE -- not where you may have been.

I think I understand. The dives here in Ontario are usually square profile, so a 500psi EAR would only happen during the last stop, never during the dive itself. With one exception I can think of, a wreck up in Tobermory that is so shallow its boiler sticks out of the water at low tide.

But for this mythical multi-level dive I have heard so much about... I get it.

 

[traumadiver]

Wow! I never expected to have so many responses to this post. I must admit that I am not the most mechanically inclined person in the world so really getting this to take off might be a bit difficult. In all reality, this was just an idea I conjured up while doing some training at work. I also must admit that my knowledge of gas laws is somewhat new and very limited. I was under the impression that if a tank is transfilled at depth, the air in that tank would increase in pressure as it ascends. However as many of you pointed out, it would not be that much of an issue because you should be no where near max pressure of the tank if you transfill.
As far as the water in the tank issue, that could be a real problem. From reading the patent it seems like someone may have already figured that one out though...I think, didn't seem very clear to me.
Many here have said there is no need for this type of device in the recreational dive world. You are probably right however there is probably a use somewhere. I look at it this way. Back in the day when firefighters were running low on air in a fire, they were forced to buddy breathe using the same mask (read regulator). Some braniac engineer came up with the brilliant idea of trans-fill and now it is the national standard. To change a national standard in the fire service is like pulling impacted molars, firefighters are resistant to change. If you think this idea has no place, I must disagree, it probably does.
Try this out for size. You got your body trapped in some hole on a reef, you are now a trapped diver. You are low on air at 200psi. since you are hyperventilating and at depth. Your buddy cant get you out so he must surface to get help. If he leaves you, you will run out of gas. You are now dependent on his octo to give you gas, you have leashed him to your side and he cant get you out. If you had transfill though your buddy could equalize with his 2000psi since he has a low consumption rate. Remember, you are hypervenitilating since you are trapped. Transfill is complete, your buddy can either try harder to free you, or surface to get more help.
Another intersting this is everyone is thinking that the transfill has to be done directly at the HP port on the 1st stage. I do not know jack about regulators but my thought would be to put a nipple, kinda like the one that connects your LPI to your BC, on the hose that connect to your SPG, I believe that would be a High pressure hose right? Not sure how long it would take to equalize though. Also, you are right, you have to control the rate of transfill because it will cool them down. I have had some really cold bottles after transfill during fire training.
I find it pretty interesting that this topic has stirred up so much debate. Must be somewhat of a good idea, lots of people are talking about it. Maybe someone with more engineering brains than I can run with this.

 

[bamamedic]

I'm all for inventive ideas...I can see where transfilling a tank could have some merit...maybe for tropical DMs who see that their charges are a lil' low on air or something.

I'd just like to point out that if you're stuck in a hole in the reef (how the heck did that happen?), hyperventilating, and with only 200psi to go, you're in a world of hurt. Transfilling your cylinder to obtain a few hundred psi extra, is only gonna delay the inevitable.

Better to spend one's time and money on training/diving in order to gain the necessary knowledge/experience to avoid the situation in the first place...

 

[h90]

there are connections which keeps dry. My father always had a couple at home, for chemical industry, when it is necessary to connect a hose with letting any trace of air in.
But my concern would be:

Diver 1 out of air
Diver 2 coming with a full 300 bar tank
They connect
due to currency or anything else the connected tanks get separated and the hose brakes at 300 bar
Diver 2s tank is changing into a rocket and propels him to the moon.....

 

[Kern]

I was under the impression that if a tank is transfilled at depth, the air in that tank would increase in pressure as it ascends. However as many of you pointed out, it would not be that much of an issue because you should be no where near max pressure of the tank if you transfill.

No, it wouldn't matter if you used a huge tank to transfill a much smaller tank that was then filled to the smaller tanks maximum pressure. The reason it's not an issue is that the tanks are rigid, the pressure of the gas inside the tank is unaffected by the external ambient pressure. It doesn't matter how much you ascend or descend, how much the pressure surrounding the tank changes, neither the pressure or the volume of the gas inside the tank will change.

 

[DA Aquamaster]

I would not be inclined to use anything with the potential to blow a droplet of water into the tank and that would be the case with an underwater transfill whip, regardless of the quick disconnect used. That is in my opinion the difference between SCBA and scuba use - firefighters are around water, but scuba divers are soaking in it for the entire dive.

It is also overkill for a small problem. I have on occassion shared gas with a diver with a much higher SAC rate on recreational dives and during technical training in a situaion where my buddy was a hoover. Ideally you do it proactively at the beginning or middle of the dive to ensure you have equal gas volumes toward the end of the dive where the hoover diver can finish the dive normally.

Gas sharing with a long hose (7') primary is very easy as normal swimming is easily done with the divers swimming side by side, and can even be done with relative ease with the divers in trail formation.

At a minimum you would need a high flow HP hose (the SPG hose is not high flow and gas transfer woudl probably not keep up with the OOA divers breathing rate), an additional HP port on the tank valve or reg, and a suitable quick disconnect system. The cost of the added transfill ability woudl come at the cost of an additional failure point. If the HP port. SPG hose, SPG etc fails, a flow restrictor ensures that the gas loss is minimal (a technical training ageny did a test that indicated 22 minutes to drain an AL 80). However with a higher flow port needed for transfill of high pressure gasses, a failed quick disconnect would mean the entire contents of the tank would be lost in very short order, increasing the risk faced on every dive.

It consequently makes litle sense when a long hose primary or slung pony bottle provides the same capability with less risk or technical complication.