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

[beanojones]

Giving the picture post another shot here.

 

[grazie42]

I am definitley going to use these as rec equipment, as the divers using them will be OW students or intro divers, or just regular old fun divers. So for me the SOP is the rec standard, not the Tech/DIR SOP.

Isnt the "rec standard" that there is no standard?
Why should "OW students or intro divers, or just regular old fun divers" have to bother reaching behind their wing when they dont have to?(left or right propably doesent matter for these divers) Why should they not learn the "tech SOP" from the start rather than "rec standard"(if there really is such a thing), when that standard is suboptimal?

I saw the ring you made in that picture...Id say that if the only gas you have, is that little corner and you cant get neutral without dumping it, then youre underweighted...

 

[Chris Brown Tech]

Isnt the "rec standard" that there is no standard?
Why should they not learn the "tech SOP" from the start rather than "rec standard"(if there really is such a thing), when that standard is suboptimal?

Totally agree. The lack of training and understanding of venting air in a horizontal position should be included in open water training IMHO. A standard position would help enormously. I always take the time to get my students used to the rear dump and get them to try it out. Much easier to slow an ascent due to loss of buoyancy with the rear dump in a slight head down position instead of having to go vertical and dump from the hose.

 

[JeffG]

I edited that first pic to circle the air trapping space that front mounting dump cause. A rear dump pulled to the rear can be pulled back to make it the highest point. IME the front mounted dump is limited by the length of the fabric, and can never dump that last bit.

OMG...on a 55 lb wing...thats like 1/10 of lb.....We are all going to DIEEEEEEEEEEEEEEEEEEEEEEE!

 

[beanojones]

Isnt the "rec standard" that there is no standard?
Why should "OW students or intro divers, or just regular old fun divers" have to bother reaching behind their wing when they dont have to?(left or right propably doesent matter for these divers) Why should they not learn the "tech SOP" from the start rather than "rec standard"(if there really is such a thing), when that standard is suboptimal?

I saw the ring you made in that picture...Id say that if the only gas you have, is that little corner and you cant get neutral without dumping it, then youre underweighted...

Because then they never learn to dive with the proper amount of weight? Because they have to go off horizontal to vent their BC?

How many reasons do you have to give to justify not trapping air in a BC?

As for why not use the 'tech SOP', there is no tech SOP. That's kind of the whole point of DIR, isn't it?: trying to set standards for tech or even all of diving.

This whole thread is a perfect example of what is wrong with DIR: In order to follow in lockstep with what they say, people seem to be willing to put up with air-trapping BCDs, which makes diver have to dive over-weighted. And diving over-weighted should be exactly the sort of thing that something like DIR should be against (it seems).

I dive without weights. Having to add weight to fix the air-trapping problems of a BC seems exactly the sort of problem gear should not introduce.

 

[Geoff_H]

This whole thread is a perfect example of what is wrong with DIR: In order to follow in lockstep with what they say, people seem to be willing to put up with air-trapping BCDs, which makes diver have to dive over-weighted.

Dude.... I'm no DIR fanboy but that is the most ridiculously unjustified anti-DIR thing I have read in a long time. I dive a BP/W and use the butt dump valve exclusively without a problem trapping any air whatsoever.

And for diving overweighted - for that tiny tiny bit of air I think you would need about 1g of lead to compensate... in reality you would never even notice it.

I dive without weights. Having to add weight to fix the air-trapping problems of a BC seems exactly the sort of problem gear should not introduce.

If I dive without a wetsuit I dive without any weight too. Nothing to do with any made-up air trapping problems - just not needed. To be honest, when not using a wetsuit I could happily dive without a wing too.

 

[beanojones]

If I dive without a wetsuit I dive without any weight too. Nothing to do with any made-up air trapping problems - just not needed. To be honest, when not using a wetsuit I could happily dive without a wing too.

But see that's the thing, the air trapping is not made up, or I would not be asking the question. There's even a picture of it. (One that I did not post.)

Why not just put the dump in back where there would be no air-trapping?

I have dove with a rear mounted butt dump since I started diving and never had problems with ait trapping. I dove the SuperWings and had air-trapping problems. I could fix those by flipping the wings.

But now the same BC I have been using for ten years has decided to move the dump to the front, and the question is why? That design traps air (I know this from first hand experience, and pictures someone else posted show why) . Is it just to do it like everyone else? Is there some functional difference that makes it worth trapping air?

 

[wedivebc]

What, no cave divers here? The reason for the dump valve being on the inside is to avoid having it face up where debris and percolation from a cave or wreck ceiling can lodge in the valve and prevent it from closing.

 

[MBH]

Giving the picture post another shot here.

Am I the only one who thinks that wing is just a touch too large for an al80. That thing is bigger than my doubles wing.

 

[Splitlip]

When you pull a front facing fabric butt dump, the inside fold of fabric is shorter than the outside so it is not the highest point.

I've been diving wings for years, and it never mattered, because the Travel Wing had the butt dump properly placed in back. And the Dual Bladder SuperWings can just be flipped so the dump is in the right place, facing away from the diver.

But now Dive Rite has moved the butt dump of the Travel Wing to the front, so it traps air.

Picture:



The blue length is the limiting length if you pull back away from the butt. If you pull on the rear facing dump it becomes clearly the highest point (which it was anyway). On the front facing dump, you have a whole bunch of bladder which can trap air since it is roughly three times the length of the limiting fabric.

This is not an idle question, because I have dove-ded front facing bladders and they trap air. Now that Dive Rite is following the other makers like sheep in putting the dump on the front,, there is no new Travel Wings that does not trap air.

So why do they put it on the front? Is everyone just doing what everyone else does? Just because?

IMO Dive Rite "fixed" a problem when they moved the dump to the front (facing diver). With the rear (facing cylinder) dump you pulled towards your body (unless you have 2 elbows)and essentially lowered the valve. It was no longer the high point when the diver is in a horizontal position.