Quote: (Originally Posted by pchanning)
OK, i'll bite
Why do they not use o-rings? If these other BOV's (KISS? - please name them) do not have o-rings for fear of chaffing/ extrusion, trapping grit, whatever, then OK I can appreciate that. But if they dont seal as a consequence, as seems to be purported, whats good about it?
The worse thing you can do to an o-ring in service is to slide across it (the action of closing the dsv)
The only o-rings that are not static in the whole Rebreather is the ones in the mouthpiece.
If this o-ring fails you can end up with a loop flood.
If this happens when you 4000ft inside a cave (as has happened to me) its not nice.
A well made close tolerance dsv does not need o-rings to seal.
The lack of o-rings takes away one risk of flooding.
The downside is the need to keep the barrel clean/more regular servicing.
If a well made close tolerance dsv leaks (because it hasnt been serviced/cleaned well) then the amount of water ingress will be very small - not a problem.
So basically you have 2 choices:
1) a o-ring seal design that is easier to seal with and requires less service BETWEEN failure - but when it fails it fails suddenly and could cause flooding
or
2) a non o-ring design that requires more service to maintain a seal - but not possible to have a SUDDEN failure - even if it leaks the amount of water that comes in is small.