Equalizing tank pressure at depth
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double entry glitch -- post repeated a couple of posts down.
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Reg Braithwaite
Contributor
Don't give up.
If this idea does not work, keep thinking and asking questions, that is how some pretty cool stuff ended up in everyday use.
OTOH - This idea could work and work underwater. It would require a redesign of the 1st stage regulator and would not be feasible to retrofit existing ones. In addition, this could be a good idea for some specialized applications as well. Again, keep thinking, ignore the naysayers.
BTW, If I'm running low, I just borrow a little air from my lovely bride, she doesn't mind.
While my wife and I don't use the OP's method of "equalizing" our air supply while diving, we often DO "equalize" our air supply while diving by the simple method of me going onto her long hosed 2nd stage. It is a simple thing to do AS LONG AS both divers have reasonable buoyancy control and understand what they are doing.
I use at least 20% more air than she does on a typical dive (although she is now getting her SAC rate down in the 0.31ft3/min area while mine will be in the 0.42ft3/min on the same dive). So if we are diving AL80s, the norm is that I'll breathe from her tank for about 5 - 10 minutes at some point in the dive. No, the dive isn't over when I go onto her supply -- we just keep swimming and looking at the pretty fishies.
The dive IS over when we finally do reach the magic 500psi number -- and, sigh, even doing this, it is most likely when I reach it! But we've both had the maximum use of BT -- and that is good.
I use at least 20% more air than she does on a typical dive (although she is now getting her SAC rate down in the 0.31ft3/min area while mine will be in the 0.42ft3/min on the same dive). So if we are diving AL80s, the norm is that I'll breathe from her tank for about 5 - 10 minutes at some point in the dive. No, the dive isn't over when I go onto her supply -- we just keep swimming and looking at the pretty fishies.
The dive IS over when we finally do reach the magic 500psi number -- and, sigh, even doing this, it is most likely when I reach it! But we've both had the maximum use of BT -- and that is good.
ScubaSteve
Wow.....what a DB
.......
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There are better options than a trans-fill.
My first choice is donate. I use a 7-foot hose, so sharing air with another diver is a total non-event. Depending on the circumstances, we may choose to ascend or simply use the shared-air as a way to extend the dive. I do the latter on vacation dives when we're trying to get as much bottom time as possible ... just make sure you tell the dive guide (if you have one) what you're doing in advance of the dive so they don't think it's an emergency.
A second option would be to carry a redundant air supply. If your buddy needs air, you simply unclip it, clip it to their BCD, turn it on and hand them the regulator. This is assuming LOA, rather than OOA ... where you have time to do things methodically.
In either case, you'll want reasonable buoyancy control and some practice at performing the skill before trying it in a real-dive circumstance. Given a moderate skill level, it's not difficult ... it's not dangerous ... and it's definitely not an emergency.
... Bob (Grateful Diver)
My first choice is donate. I use a 7-foot hose, so sharing air with another diver is a total non-event. Depending on the circumstances, we may choose to ascend or simply use the shared-air as a way to extend the dive. I do the latter on vacation dives when we're trying to get as much bottom time as possible ... just make sure you tell the dive guide (if you have one) what you're doing in advance of the dive so they don't think it's an emergency.
A second option would be to carry a redundant air supply. If your buddy needs air, you simply unclip it, clip it to their BCD, turn it on and hand them the regulator. This is assuming LOA, rather than OOA ... where you have time to do things methodically.
In either case, you'll want reasonable buoyancy control and some practice at performing the skill before trying it in a real-dive circumstance. Given a moderate skill level, it's not difficult ... it's not dangerous ... and it's definitely not an emergency.
... Bob (Grateful Diver)
My thoughts:
1. It would require some specialized equipment beyond just the transfill whip. No problem, that's what's the hypo is about.
2. Water entering the tank doesn't have to be a problem. You've got several hundred/thousand PSI going through the whip. I can imagine you hook up the device and there could be a mechanism to blast out any water using the pressure from your tank before opening the valve to his tank. Would it work? Dunno, but it seems like a plausible solution.
3. It's a time consuming process. Even if it were as efficient as an isolator valve on a manifold, you've got to signal, pull the junk out, hook it up, purge, equalize. It's fine if your buddy is low on gas and not out, but it's wholly useless in a real gas emergency. Also, if your 800psi goes into his 200psi and you're both stuck with less than 500psi each, probably less once you take the time to get this going and done with. Is that really a better solution to take the time to do all this than immediately donating an octo and ascending?
4. Is it good to send a lot of gas through at depth? For colder dives, would there be concerns with freezes/freeflows due to adiabatic cooling?
RB depends on the depth and the capacity/rated pressure of the tanks you have (as well as your DCR, but there are some decent guestimates to use for that). We typically use around 500psi in small doubles for dives under 60ft, or after we have finished the deep segment of our dive and are back on the shallow reef. If we dove to 100ft with single AL80s, our rock bottom would be more like 1600psi.
But I think Peter was just saying that regardless of what your rock bottom is, it's not a bad idea to end the dive with enough reserve to 1) account for inaccurate pressure gauges, and 2) have enough gas in case an issue or emergency dictates that you should descend again, like if an upside-down helicopter is strafing along the surface.
1. It would require some specialized equipment beyond just the transfill whip. No problem, that's what's the hypo is about.
2. Water entering the tank doesn't have to be a problem. You've got several hundred/thousand PSI going through the whip. I can imagine you hook up the device and there could be a mechanism to blast out any water using the pressure from your tank before opening the valve to his tank. Would it work? Dunno, but it seems like a plausible solution.
3. It's a time consuming process. Even if it were as efficient as an isolator valve on a manifold, you've got to signal, pull the junk out, hook it up, purge, equalize. It's fine if your buddy is low on gas and not out, but it's wholly useless in a real gas emergency. Also, if your 800psi goes into his 200psi and you're both stuck with less than 500psi each, probably less once you take the time to get this going and done with. Is that really a better solution to take the time to do all this than immediately donating an octo and ascending?
4. Is it good to send a lot of gas through at depth? For colder dives, would there be concerns with freezes/freeflows due to adiabatic cooling?
Is 500psi a typical "rock bottom" for your dives?
RB depends on the depth and the capacity/rated pressure of the tanks you have (as well as your DCR, but there are some decent guestimates to use for that). We typically use around 500psi in small doubles for dives under 60ft, or after we have finished the deep segment of our dive and are back on the shallow reef. If we dove to 100ft with single AL80s, our rock bottom would be more like 1600psi.
But I think Peter was just saying that regardless of what your rock bottom is, it's not a bad idea to end the dive with enough reserve to 1) account for inaccurate pressure gauges, and 2) have enough gas in case an issue or emergency dictates that you should descend again, like if an upside-down helicopter is strafing along the surface.
No, the connection whilst in process of being made wouldn't be under pressure (other than ambient water pressure). Water WOULD get in. In any case, such a connection to be effective would have to be either between low-pressure ports or completely before the regulators. The HP ports are way too restrictive. I can think of countless things that could go disastrously wrong.
If you're in a position where one person has significantly less air than the other, then what's wrong with sharing air the old-fashioned way? Once one diver gets to low air in absolute terms the dive must be over anyway.
I checked the date of this thread. It would be ideally posted on 1st April.
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