Why do Tech BC's have the butt dump on the inside, not the outside?

[Splitlip]

(Actually, the vast majority of the world mounts the butt dumps in back. It' only the 'tech' BCs that mount it in front. Hence, this thread, wherein I ask why 'tech' BCD's do it differently than the rest of the world.)

If you look at the picture I circled the trapped air in, the diver would have to roll pretty far over on his side to vent it using the front mounted dump. It is kind of like a ziploc bag of air in there, with the added problem that a front mounted dump has too little fabric to allow it to escape since it cannot be pulled to the highest point. A rear mounted dump can be pulled to the highest point.

BC's like Jackets can and do mount them that way because they have to. The cell is wrapped around the body (or in some cases bunged like some Zeagles)

Mounting the OPV inside a jacket would not work.

Sorry. Missed part 2.

You are not going to be able to use a rear facing dump very effectively with the wing in the picture. Unless you have 2 elbows and monkey arms.
With a front facing dump, you will do much better because you should have an easier time reaching it and some room to pull it.

Actually that wing is a really bad example for an illustration. It is way too much wing for a single.

The Oxycheq pic is a much better example of properly use.

 

[beanojones]

Not just a matter of reaching it, but using it effectively.

If you look at the pic of the Red Rec Wing above, clearly it is a reach to get to the string. Once you get the string, the flap in the OPV is pulled away from the wing to exhaust. It would take some kind of monkey arms to pull or push the string in the picture away across the cylinder.
The other option in this case is to get the string an pull towards you or sideways. When you do that the dump is no longer in the high part of the bubble.

Some of the older DR wings even had the dump facing away from the diver but the string and ball were threaded around the wing to face the diver. This to me made no sense unless the diver was pointed head down.

I gotta say this must be a wetsuit/drysuit difference. I have never had any problems touching the bottom of my tank, and I never had any problems pulling a butt dump on wings. Not when diving singles with flipped Super Wings, not with diving singles with the Travel Wings, not with diving twin 130s and two slung 67s with the flipped Super Wings. Then again I never have worn a drysuit. I have had air trapping problems with diver facing dumps (which is why I flipped the SuperWings). Then again I dive wetsuits without weights so I do notice the odd pound or five of trapped buoyancy in them.

I still have no idea what is hard about reaching the dump. I really have no idea what the 'two elbows" that have been mentioned a couple of times refers to.

As far as the tied down ball, we always used that string loop as the pull rather than trying to find the ball. (Maybe there again, bare fingers versus gloved hands and all that?) We certainly would not look for the ball, because as you mentioned pulling that would pull things in the wrong direction. We just pulled the loop of string up away from the body. Again if it is hard for some reason to touch the bottom/back of your tanks in a drysuit, or to have feel for things like strings with gloved hands, that may be a difference. But if you have that little feel in drysuit gloves, everything but the inflator seems like it would be hard to use. How can you even tell when you have a pull ball in your hands?

I guess in the end, the question still lives: Regardless of whether any particular diver can reach a butt dump, rear facing or not, why put it anywhere, if it traps air? Why not just leave it off, eliminate a 'failure point', and let the diver use the inflator?

 

[cool_hardware52]

I guess in the end, the question still lives: Regardless of whether any particular diver can reach a butt dump, rear facing or not, why put it anywhere, if it traps air?

It may still "live" in your mind. For most of the rest of us this question has been answered repeatedly, then for good measure beaten to death.

Why not just leave it off, eliminate a 'failure point', and let the diver use the inflator?

Have you ever, in your vast experience, encountered a BC made in the last 20+ years, that did not have AT LEAST ONE Over Pressure Valve?

Without an OPV what do you think might happen if a diver "leaned" on the power inflator?

Beano,

Given the totality of your posts, in this thread an elsewhere, I'm willing to say I do not recall anyone else, who purports to dive and teach in a BP&W who is so completely and potentially dangerously ignorant about BC's in general and BP&W's specifically. It's truly head spinning.

Your demonstrated intransigence and ignorance is breath taking.


Tobin

 

[Splitlip]

Sorry Beano. Guess maybe I need video.
I am a relative NOOB to BPW's compared to some of the guys posting here. I have used the old Dive Rite venture wing though, in addition to several others. The Dive Rite was what it is. All jacked up.

What's a drysuit? I live in South Florida.

I am done.

 

[beanojones]

AT LEAST ONE Over Pressure Valve?

So is the dump really just there as an OPV then? Not as a dump?

 

[JeffG]

So is the dump really just there as an OPV then? Not as a dump?

You're an instructor?


God help us.