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Thorn (tthorn)wrote:-
>Does anyone have a fix for the "airhead" <G> problem with the Viking
hood?
>What actually causes it?
Causes:-
1)On descent, air is drawn ('sucked') from the mask into the hood which
then expands on the ascent. If the hood squeezes while descending,
causing discomfort at your ears you can face downward and exhale through
your nose to introduce even more air into the hood, but at least it takes
away the pain!
2)Further hood inflation can be caused by a leaky neckseal. This would
cause hood inflation at depth, rather than during the ascent. The only
solution in this case is to repair or replace the neckseal.
3)If you use a positive pressure FFM, a loose fitting hood will be
inflated immediately - the only solution I've found for this is to find a
tighter fitting hood. If you can get the mask to fit better on you face,
this might be sufficient.
Ways to get rid of the expanding gas on ascent:-
1)A lot of people fit dump valves of one sort or another (eg the simple
'Draeger' type dump as fitted to drysuits) - this works fine but can be a
source of water ingress. Don't use this as a cure for the FFM problem -
the howling gale through the hood will take a lot of heat with it and
you'll have to carry extra gas because of the waste. You don't have to
fit the dump valve right on top of your head, as I've seen several times
although this does have the advantage of making you look REALLY stupid
(Replace the Air-Head with a Tit-Head).
2)If you tilt your head back and breath in through your nose during the
ascent you can rebreathe the gas in the hood and then exhale into the DV.
3)If breathing the gas doesn't appeal, tilt your head back and squeeze
down on the gas bubble - the gas will vent just below the mask seal at
your cheek. This can be a pain and it confuses the hell out of your buddy
if they've got a wet hood (they think your suffering some kind of severe
headache!)
Usually, if the hood is a fairly tight fit, the gas will vent on its own
by passing into the mask and leaking from there in the normal way.
Unfortunately the model for the Viking hood was obviously large.....
Ian McLean
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