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> 
> I friend of mine has a Scubapro Mk20/G250 reg. Up here in Sweden
> it's icy and cold at the moment. His reg. freezes all the time
> making it freeflow. The first stage is fitted with the SPEC kit
> (anti freeze). Only the main 2nd stage freeflows - does this
> mean that it's the 2nd stage that freezes or is it the first
> stage? Scubapro tells us it shouldn't happen... Is anybody out
> there experienced in cold water diving that knows?

Over the years I have done alot of cold water diving both rec and commercial 
with a variety regs and have yet to see a reg that "can't" freeze.  Some 
however appear to be more prone then others.  From my experience it is 
usually the 2nd stage that freezes in the open position.  From experience 
this is how I belive it happens.  
Water gets into the 2nd stage, either by letting the 2nd stage out of 
your mouth and allowing water in or even the condensation from the 
exhaled breath.  Water or condensation will eventually work its way to the 
downstream demand valve in the 2nd stage.  When the valve opens there is 
a significant temperature drop due to the expanding air/gas.  The 
water/condensation in the 2nd stage then freezes.  Now if/when a bead of 
ice forms on the valve seat it prevents the valve spring from closing the 
valve tightly.  At this point things begin to happen quickly.  With a constant
leak the metal around the valve seat gets colder allowing more and harder ice
to form. After each breath the ice build up just gets worse, making for a 
harder and harder freeflow.

As for the 1st stage freezeing, very unlikly unless somehow water has got 
into the High Pressure chamber, possiblely from carless handeling of the 
reg prior to mating to the tank valve.  I have surfaced many times with a 
centimeter or more of ice encrusting the lst stage and valve with no 
problems.  It does however prevent the air from being turned off or the 
reg from being removed until the ice melts.

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