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> Do you have any experience with Poseidon Jetstreams (Odins) with their 
> upstream servo 2nd stage freezing
> 
> I have heard a couple of unsubstantiated tales of them freezing shut.
>
Sorry but No.  Don't own one, never used one, don't know anyone who does. To 
tell the truth never even seen one. But I have heard the name.

The only input on the matter would be do they have a similar internal 
mechanism to the old Cyclone 300's? Which was very different to most 
"tradional" disigns. The Cylcone 300 I have seen/used and they appeared 
quite reliable in cold water. 

 
> On the general subject of 1st stage freezing, is it not possible for the
> ambient spring chamber to freeze solid, clamping the main spring, preventing
> the 1st stage from shutting?
> Is this not why we put environmental seals on and fill the chamber with

Just as an aside my most used reg is a DACOR PACER XL. And I don't bother 
with the cold kit.  Just a few common sense rules when handeling it in icing 
conditions has always left me the last one out of the water

> anti-freeze solution?

The only case I have observed of a 1st stage freeze up.  Was in a reg 
that was regularly "blown out" by its owner.  For a while it was common 
practice with some of the less informed, after a dive to remove the 1st 
stage from the tank valve, then crack the tank valve. Presumable the 
intent was to blow water/debris/etc off the 1st stage valve seat.  When 
infact they were blowing a small amount of water into the reg.  Small 
amount of water then gets into the High Pressure chamber in the 1st stage.
On demand the 1st stage piston moves to admit air, the temperature drop 
associated with the pressure differential causes that trace to freeze on 
the piston wall thus preventing the piston from returning to the closed 
position.  This allows tank pressure air through to the 2nd stage which 
was never designd to take that much pressure.  The downstream valve is 
simply force open by the overwhelming pressure.  A very different and 
unmistakable occurance from a 2nd stage freeze up. 

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