What if DIR Evolved Elsewhere... (take two)

[Steve R]

Then I guess you are also worried about having the same problem with your dry suite inflator. They are both essentially the same thing.

Not really, or at least not in practice.

I can imagine there's a certain amount of body heat being thrown off into the dry suit mechanicals that may make for dry suit runaways not as much of a problem, and what's more, it's infinitely easier to spin closed an argon bottle.

 

[Thalassamania]

Not really, or at least not in practice.

I can imagine there's a certain amount of body heat being thrown off into the dry suit mechanicals that may make for dry suit runaways not as much of a problem, and what's more, it's infinitely easier to spin closed an argon bottle.

I think they are pretty much the same problem as long as there's a regulator in the line, Fenzys and A.P. Valve systems get around this with BC's by having a true direct feed from a small cylinder at full tank pressure to the BC.

 

[Steve R]

The first stages has an OPV, and we use low-flow QD's. In practice it's just not the problem BC's are.

If it "goes off" it'd be when you were inflating it, you'd more than likely hear it as well as feel it. If the inflator didn't allow for quick disconnect (Never seen a ball of ice on the suit, but certainly have on the BC inflator) the argon bottle is a piece of cake to get at.

If you haven't seen any BC Inflator issues, I doubt you've seen any suit ones either.

 

[Thalassamania]

The first stages has an OPV, and we use low-flow QD's. In practice it's just not the problem BC's are.

If it "goes off" it'd be when you were inflating it, you'd more than likely hear it as well as feel it. If the inflator didn't allow for quick disconnect (Never seen a ball of ice on the suit, but certainly have on the BC inflator) the argon bottle is a piece of cake to get at.

If you haven't seen any BC Inflator issues, I doubt you've seen any suit ones either.

So I guess if you're going to use a "detunable" regulator installing an OPV on the 1st stage would be a good idea, but I can hear it now ... another failure point, a solution in search of a problem, etc., etc., etc. Perhaps "detunable" regulators that don't blow open at 200 PSI or less should go the way of upstream valves.

 

[amascuba]

Earlier this year when the incident with the free flowing regulators and run-away inflater's happened in Ontario there was allot of speculation concerning the the intermediate pressure of the first stages. On the quest list JJ went asking around for an answer and here is what he posted about it on the quest list.

Hey gang,

It took longer than expected but here is a summary opinion for consideration
regarding INP and freezing.

Jarrod,

Intermediate pressure: how it affects second stage performance

First define adiabatic expansion (ideal case in which no work or heat is
transferred):

The product of the temperature (in degrees Kelvin) and pressure elevated by
the exponent (1-gamma)/gamma, where gamma is the ratio of specific heats
(specific heat at constant pressure over specific heat at constant volume)
is the same before and after the expansion. Hence, since the pressure during
the expansion decreases, so will the temperature. Gamma for nitrogen oxygen
mixes is approximately 1.4.


Note that this is a very ideal case, representing the maximum possible
cooling. In reality, due to heat exchange the actual amount of cooling is
significantly lower. Still, this is a good way of estimating the maximum
possible cooling due to the expansion.

Lowering intermediate pressure has the following effects:
1) in the first stage: it increases cooling due to higher adiabatic
expansion. Effect is negligible since the pressure ratio hardly changes.
Example: expansion from 200bar to IP of 10bar at 40m, vs expansion from
200bar to IP of 9bar at 40m, starting at 20 Celsius
a. T2=293*(200/14)**(-0.286)=137K=-136C
b. T2=293*(200/13)**(-0.286)=134K=-139C
2) in the second stage:
a. due to adiabatic expansion: decrease in cooling due to the lower
adiabatic expansion. More noticeable effect than in first stage due to the
initial and ending pressure being closer in value, but not by much. Example:
expansion for an IP of 10 or 9bar at a depth of 40m, assuming again an
initial temp of 293K:
i.
T2=293*(14/5)**(-0.286)=218K=-54C
ii.
T2=293*(13/5)**(-0.286)=222K=-50C
b. due to reduction of positive pressure during inhalation: less
fluttering of exhaust valve hence less likelihood of water droplets entering
into the second stage


All in all, the lowering of the IP should have little or no effect on first
stage, whereas even one degree temperature difference might be of importance
in the second stage. Still, what isn¹t there cannot freeze.

 

[grazie42]

I´ve actually thought about having a manual inflate for the DS, just like on the bc...
As far as I´m concerned the DS is a bigger problem because it doesen´t vent as fast nor is it as easy to disconnect...as there´s often no rush to inflate, a manual inflate would propably work well in more benign conditions as well...

Alternatively having one of these makes things easier to disconnect:
Dyk & Brand Service Sweden AB online webbutik för Sportdykare - http://www.dyk-brand.se

 

[Thalassamania]

I´ve actually thought about having a manual inflate for the DS, just like on the bc...
As far as I´m concerned the DS is a bigger problem because it doesen´t vent as fast nor is it as easy to disconnect...as there´s often no rush to inflate, a manual inflate would propably work well in more benign conditions as well...

Alternatively having one of these makes things easier to disconnect:
Dyk & Brand Service Sweden AB online webbutik för Sportdykare - http://www.dyk-brand.se

Some early suits came with an oral inflator (e.g., O'Neil Super Suit, Poseidon JetSuit). Not the least of the problem was the jet of water that went in with each breath.

 

[Gilldiver]

So after looking at the above, and not much else, the inflator freezing issue seems to be a fresh water phenomenon and is limited to cold water lakes. This would also explain why the cold water people that I know (McMurdo Sound, Antarctica) don't see it as they are almost wholly in a salt water environment.

Now a further question, do you see the icing phenomenon on plastic body inflators or only metal ones? The heat transfer of metal is much higher then the plastic which should result in an earlier onset of icing and perhaps a great total amount. If this is correct, it would also explain the much greater occurrence on BC inflators over drysuit inflators (are there any metal body dry suit connections?).

Finally, if the above is true, then there would need to be an adjustment to gear configuration, say something like:

1) When cold fresh water diving at temps of less then (TBD but lets say 36F/2C) should only be conducted with plastic body BC inflators or with the BC inflators disconnected from a compressed gas supply.
2) When cold water diving in fresh water BC and Dry suit quick connections should be equipped with large surface area knobs to aid in connection and disconnection of them when using cold water gloves/mitts.