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Dale,
I took a closer look at this icing situation last night.
You said:
>Certainly, a high flow first stage regulator has the potential for
>a greater cooling effect. The reason we want high flow regulators
>is to have that flow available during those stressful times when it just
>might be needed. Sure, you could limit the potential for freezing by
>limiting flow but then you just might not get the air you need in a tight
>situation. The key is to design a regulator that is capable of high flow
>while incorporating design features that protect against freeze-ups.
Exactly ! And the Poseidon Odin is it!
>Higher intermediate pressure causes a greater cooling effect in the
>second stage, not the first. The cooling effect is due to the gas
>expansion. When the intermediate pressure is higher, there is a
>correspondingly greater gas expansion in the second stage.
Right! As I said ;
" Would this not be similar to the situation presented by a high intermediate
pressure that results in a greater drop in pressure from intermediate to
ambient and, therefore, a greater chance of forming ice in the second
stage ? "
> Poseidon regulators do, indeed, throw ice at
>the diver, but that ice is produced in the second stage. With their upstream
>design, ice forming in the air stream would probably cause stoppage of the
air
>flow altogether.
But they do not, according to reports from divers using them. They simply
continue to throw Ice. Seems like the best possible situation to me - even if
ice does form it does not alter the ability of the regulator to deliver gas.
What
more could you ask for?
With the Poseidon Odin pilot valve gas is not expanding inside a closed or
confined space within the second stage as it is in the typical down stream
design. Any ice that forms is, therefore, outside the mechanism so that it
"throws" ice slivers but does not "jam" the mechanism. With the down stream
design ice is able to form and build within the chamber around the popet
spring and hold it open. Until this basic design "flaw" is changed all
typical down stream designs will be inferior for ice diving where the
potential for free flow is concerned and attempts at changes in materials
to solve or reduce the problem are half assed corrections of a basic design
problem at best. Look at all the so called "cold water" regulators that
reportedly
don't work reliably.
>...In fact, a buddy of mine had a poseidon second stage blow
>right off of the end of his hose due to icing. This occurred at Lake Geneva
>Wisconsin this last December on a day when the air temperature was somewhat
>below freezing. Following his dive, he left his equipment laying on the
>ground while he changed into warm clothes. When he went back to pick up his
>gear he turned his air back on. There was a bang that sounded like a gunshot
>and the regulator second stage shot off the end of the hose. It flew 30 feet
>through the air. It had been attached to a 7 foot hose that was now whipping
>around wildly. Another dive buddy was struck smartly with the hose and
>stumbled into the lake. When we sorted everything out it became apparent
what
>had happened - The regulator first stage had frozen to free flow and the
second
>stage had frozen closed. This caused the intermediate pressure in the hose
to
>rise to tank pressure, resulting in hose rupture.
This must have been one of the pre relief valve Poseidons or
ice formed in the relief valve mechanism while sitting on the surface
after the dive just as it obviously did around the first stage spring
when he bled the second stage after shutting the gas off (I am assuming
that this was an Odin regulator - the shower head). This is an upstream
valve, always closed against IP, and only the relief valve provides
protection against the dangers of IP overpressure, as you obviously know.
When you bleed off the second stage after turning off the tank
valve you also bleed the tank pressure from the HP chamber of
the first stage into the IP chamber and hose so that you have
opened the spring loaded seat between the two. Apparently the
spring froze into this open position instantly upon the expansion of
gas from the HP chamber of the first stage while on the surface
with some water still in the spring chamber. Don't know how this could
happen if the first stage was protected with alcohol or silicone -
perhaps it was breached somehow or the first stage failed in some other
way.
I suppose one would want to clear any water from any regulator or
BCD valves and mechanisms as soon as they exit the water on ice
dives.
I suggested that if you could move the same volume of gas with a lesser
change in pressure the chance of icing by adiabatics in the second stage
would be reduced. Though this is true, de-tuning a regulator to reduce the
intermediate pressure will be no help to an ice diver because you will also
reduce the temperature of the gas reaching the second stage by virtue of
having dropped the pressure more through the first stage. No net gain !
In the final analysis you are expanding gas from tank pressure to
ambient pressure with a specific and unavoidable change in temperature
of the expanding gas. You can alter the degree to which temperature
changes at certain points in the process by controlling the location and
amount of expansion but at the rates that it must be moved the gas will
carry the net effect of these temperature drops throughout the system as
a whole before there is time for the gas to absorb enough heat from the
ambient environment to make an effective and useful difference to the
diver.
The pilot valve of the Poseidon Odin, designed by Sweeds diving in
ice water as a matter of course, strikes me as a good solution to
second stage icing problems - let it ice all it wants just so it stays
out of the mechanism of delivery. Instead of trying to deal with ice
they rendered ice a non-problem by keeping it away from the delivery
mechanism.
PS Just read your post that identifies the first stage as a Sherwood but I'm
posting this as is anyway.
Chuck Boone
--
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