tangent on problems reaching valve(s)

[Akimbo]

… Does anyone care to offer their theory as to why valve(s) are positioned behind the diver's head?

Not a theory, it is the cheapest. Valve-up is “good enough” for the vast majority of a very small customer base. That customer base is spending leisure money compared to fire fighters that need to get a job done under difficult conditions.

The minute percentage of divers that use doubles, let alone in demanding conditions, is such a small market that manufacturing and marketing costs dictate prices that are well above what the vast majority are willing to pay. All that leaves is home-brew solutions made by individuals for personal use… sort of like the first backplates for cave divers.

I have valve protectors mounted, similar to the ones used for under-ice diving. Any other theories ?

I’m not familiar with these, got pictures?

 

[Glenn08]

If you look at Akimbo's post of the twin tanks with the two hose regulator there is a comment about the positioning. The two hose regulator delivered air at ambient pressure and needed to be located at a depth very close to the diver's mouth so that it would not free flow or require too much effort to inhale. The single hose regulator put the second stage at the diver's mouth, so it was not necessary to locate the valve and regulator (first stage) at the same depth as tha diver's mouth. Comments ?

 

[Akimbo]

If you look at Akimbo's post of the twin tanks with the two hose regulator there is a comment about the positioning…

I don’t understand. There are no double hose regulators on any of my double sets.

 

[NAM001]

Has anyone got a source for the valve protectors like in the pictures?

As for the question of why fire fighters have thier valves down. With the bulk of the gear they wear they cant reach behind thier heads.

 

[Akimbo]

Has anyone got a source for the valve protectors like in the pictures?... .

The only commercially available protectors I am aware of are made by Custom Divers in the UK.



Some of the firefighting and mine safety SCBAs don’t have separate valve protectors. Protection is built into the valve itself and a rubber bumper is added. Some rebreather valves come with a little button-bumper on the valve, but they are really small compared to the ones I have seen on single cylinder SCBAs.

This brings up an interesting question: Has anyone investigated using a SCBA valve on a single SCUBA cylinder?

I made the protectors on the white doubles in my shop from Aluminum, which are way too primitive for a commercial product. Those are my first prototype and I am working on an improvement that is lighter and easier to make.

The protector on the blue doubles is standard on Interspiro doubles.

…As for the question of why fire fighters have their valves down. With the bulk of the gear they wear they can’t reach behind their heads.

Bulky gear is certainly a factor, as it is on drysuit divers, but my understanding is the biggest reason is to protect the regulator, hose, and valve. Firefighters are more likely to accidently bang the top of their cylinder into an obstruction or have stuff fall on them than to fall on their butts.

This is the same reason most surface supplied divers wear their bailouts valve-down, even though many don’t have any protectors at all. Most bailouts are small and they have a tender to help them dress.

 

[Glenn08]

Akimbo; You posted a link to Baby Doubles, where simonbeans posted a picture of twin 45's with a two hose regulator. I will look to see if I have any pictures of my rig.

 

[captain]

I don’t understand. There are no double hose regulators on any of my double sets.

Double hose regulators were the first successful scuba demand regulator and it needed to be located near the depth level of the mouthpiece in order to function so it was placed on top and there was no real reason to change when the single hose regulator came into use. To change would have necessitated some type of valve protector/stand that would increase cost/complexity. Why do we drive on the right and the British on the left, because it's always been that way.

 

[Akimbo]

Akimbo; You posted a link to Baby Doubles, where simonbeans posted a picture of twin 45's with a two hose regulator...

Thanks, now I get it.

Double hose regulators were the first successful scuba demand regulator and it needed to be located near the depth level of the mouthpiece in order to function….

I understand the necessity of locating the double hose regulator diaphragms high, but most of the rigs used by Cousteau and the Calypso used were valve-down triples and quads using double hoses… and some high pressure tubing to make it po$$ible.

I don't think that is the big reason for valve-up today though. Several valve-down products have be marketed over the years and didn’t sell that well. I don’t think it was due to tradition because several of them were really cool looking, comfortable, and a lot of people desired a set. Cost was the show-stopper. It comes back to what is “good enough” for the vast majority who are spending limited recreation budgets.

There are barely enough valve-up doubles divers to keep manufacturers interested. From all I have read it was like pulling teeth to get a manufacturer to make the first manifold for two regulators with an isolation valve. The numbers were too small to justify engineering, tooling, and production costs.

 

[captain]

Cousteau's triples used tanks with opening at both ends. The outboard right tank had a valve on the bottom, this was the reserve tank. The middle tank had a valve at the top to mount the regulator and also to fill all three. All three were manifolded together on the bottom. The top of the right and left tank were plugged. What looks like a manifold at the top is a tie bar that holds the tanks together in place of bands, there is also a tie bar at the bottom. In essence they were diving twins with an integrated pony tank. In total it was about 120 cu/ft.

http://vintagescuba.proboards.com/thread/2817/cousteau-triples-survive

 

[Akimbo]

Cousteau's triples used tanks with opening at both ends…

It is interesting how they were comfortable with their bottom valve and manifold so exposed, especially on some of those super tall cylinders they used for a while. Walking around a boat was bad enough but they did a lot of shore dives in the early days too. It isn’t so much falling on your butt as loosing balance and banging against benches and gunnels.

Just to round out the discussion, Cousteau’s earliest triples were double-ended but they stared using single-ended cylinders fairly quickly. They were pretty creative and would mix a lot of rigs valve-up and valve-down, before and after the fiberglass cowlings came along. All the rigs I remember seeing had their reserve cylinder valve down.

The quads they used on Conshelf II in the Red Sea (World Without Sun book and movie) had the two inner cylinders valve-up and the two outer valve-down, but raised about 4". That provided pretty decent physical protection for both sets of valves. Naturally, HP tubing had to run from the two outboard valves up to the top center manifold where the regulator mounted. There are quite a few photos in the book where they used single hose regulators, but mostly for off-camera work.

It really isn’t that big a deal to run high pressure tubing between valves… except for giving people at the LDS heart palpitations.