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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.
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. 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 airstreem would probably cause stoppage of the air
flow altogether. 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 freeflow and the second
stage had frozen closed. This caused the intermediate pressure in the hose to
rise to tank pressure, resulting in hose rupture.
In a message dated 98-02-17 10:33:08 EST, CHKBOONE@ao*.co* writes:
<< Just wondering if you really want a high flow rate in a cold water
regulator ? 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 ? With the high flow you would be transferring heat from the
mechanism to the gas faster because of a higher material flow rather than
because of a greater temperature change as in the case of the high
intermediate pressure.
The only time a high flow rate might be a problem would be if you were
passing a regulator off to another diver and it free flowed in the process or
any similar case that allowed it to flow much beyond what breathing would
induce.
Of course, the flow rate capability of the regulator wont matter if you
never allow it to free flow.
The Poseidons are high flow regs with a good cold water reputation though
they are reported to throw ice crystals from the second stage at times. I'm
not sure but this could be less of a danger with the Poseidon because of the
pilot valve design - perhaps it tends to blow the ice away from the seat
before it can cause a problem and this may not be the case with some typical
down stream designs.
I'm sure that the flow dynamics through the final second stage orifice
would be a factor but I'm not sure what one would look for to reduce the
chance of forming ice.
It seems that a large final orifice moving a relatively low intermediate
pressure of gas but at a higher volume would be the best bet for preventing
icing and getting a higher than usual flow as well.
Just thought I would throw this out for consideration, hope it's not off
base !
>>
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