tangent on problems reaching valve(s)

[Glenn08]

Another post asked questions about techniques to reach the valves of back-mounted tanks. I decided to change my rig to mount my twin 50's valves-down so that I could reach the valves easily. Apparently valves-down is still a rare setup. I have a theory as to why scuba tanks are typically worn with the valve(s) behind the diver's head. Does anyone care to offer their theory as to why valve(s) are positioned behind the diver's head ?

 

[Tortuga68]

It's generally easier to put twins on when you can sit them down on their ends and not have to worry about smacking the regs

 

[Glenn08]

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

 

[Akimbo]

My preference is valve-down. Aside from being easier to reach they are far better protected from damage. The white doubles are a home-brew and the blue are AGA 324s from the 1970s.

It's generally easier to put twins on when you can sit them down on their ends and not have to worry about smacking the regs

Agreed. I would go as far as saying valve-down is dangerous without a protector. They don't have to be limited to doubles, just look at rigs fireman wear.

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

I have not seen these, can you post some images? There is a bracket made in the UK for doubles and singles.

 

[Glenn08]

Akimbo; I was impressed by your rig - looks a lot like my twin 50's. I also noticed that firemen wear their tanks valve-down. The thread about reaching valves had lots of suggestions, but my suggestion to change to valves-down was mostly ignored. It made me wonder if anyone had a theory about why valves are typically behind the diver's head.

 

[Akimbo]

The white cylinders that are farther apart are Faber LP-45s and the ones that are much closer together are Faber HP-72. I think Faber is selling LP-50s now that are about the same size as the 45s. The AGAs (not Interspiro) are really slick at 4.33" in diameter and 22" tall.

The white doubles use 190mm isolation manifolds versus the standard 215mm. One of the considerations of a valve-down design is using cylinders that are short enough that you can comfortably reach the valves. It is easier to shift the cylinder up to reach the valves than on a valve-up design, but I always recoiled against the compromise.

I am pretty short, but have abnormally long arms so my ergonomics are difficult to recommend to others. The best thing is to mount your cylinders valve-down and gently see how they work for you. If it does, consider making a protector.

I am working on a refinement of the protector on the white double now. I really like the built-in handle. A restriction of this design is regulators must be DIN — not enough space for yokes.

 

[MalibuJerry]

okay, I'll bite. first, rebreathers typically have valve down and regulator protectors. second, with doubles the isolator valve is easier to reach valve up (maybe, but with valve protectors on valve down I would think so). Third, single tank diving is usually done without reaching back for the valve, up or down, so having a boot at the bottom for stability and protection when putting it on is good, and Fourth, the tank slopes away from the body at the top resulting in more freedom of head movement. This might not be true with little chiquita tanks as in the picture, but is probably true for larger tanks.

 

[Akimbo]

… second, with doubles the isolator valve is easier to reach valve up (maybe, but with valve protectors on valve down I would think so)…

I labored under the same misconception before experimenting with these rigs. The isolation valve is very easy to reach. Normally the protector rests against your butt and the post valves are unrestricted like on a rebreather. All you have to do is lean forward a little and the bottom of the cylinders rotate away from your butt making it really easy to reach. On longer cylinders you can lean forward and a little to one side and the isolation valve swings right into your hand.

…This might not be true with little chiquita tanks as in the picture, but is probably true for larger tanks.

My first experiments were on HP-100s. I just don’t need to pack that much gas. It was very difficult for me to reach the isolation valve when standing on deck and a bit of a stretch to reach the post valves. However, it was really easy to shift the rig a little in the water to reach all the valves. Naturally reaching all the valves when sitting on the boat was super easy.

Cousteau’s cylinder sets were all valve-down. They didn’t have isolation valves, but one cylinder was equalized for reserve gas. Some of their rigs had very long cylinders. I use the isolation valve for the same purpose with a technique called Progressive Equalization. Here is a post from the Solo Forum that has restricted access:

I have been using progressive equalization since learning the technique from ex-British Navy divers around 1974. We didn’t have isolation manifolds then but did have doubles with individual cylinder valves that manifolded together to support a single regulator. A lot of doubles in Scandinavia and northern Europe were like that, as well as doubles in the US with an inexpensive adapter manifold. I preferred the adapters to the standard US doubles manifold which used metal to metal seats instead of O-rings in those days.

My most recent sets of valve-down doubles were built because complying with the SDI solo card requires a redundant gas source. Of course modern doubles with an isolation manifold and two regulators meets the criteria. I got the solo card to let charter boat skippers off the liability hook. Probably about 80% of my recreational dives have been same-ocean-buddy or nobody-on-the-beach solos most of my life.

To be honest, I am more comfortable with them. I would be perfectly happy to dive solo with a single regulator but progressive equalization makes it pretty darn difficult to get distracted and run low on gas.

View attachment 113865

Progressive equalization is discussed in these posts:

Nigel's twinset rig

http://www.scubaboard.com/forums/ad...y-bailout-strategies-recreational-diving.html

http://www.scubaboard.com/forums/tanks-valves-bands/393392-double-valve-single-tank.html

http://www.scubaboard.com/forums/vintage-equipment-diving/397498-baby-doubles.html

http://www.scubaboard.com/forums/tanks-valves-bands/399622-isolation-manifold-question.html

http://www.scubaboard.com/forums/tanks-valves-bands/394714-custom-manifolds.html

http://www.scubaboard.com/forums/ad...-cant-reliably-reach-doubles-valves-help.html

http://www.scubaboard.com/forums/ba...cuba-tanks-set-up-like-firefighters-scba.html

This isn’t rocket science. Everybody wears cylinders valve-down except most scuba divers, especially in the US. Just mount your backplate up-side-down on your doubles and carefully put them on. If that is interesting, put a longer hose on your inflator and use them in the water, assuming you have long hoses on your regulator (my suit inflator and SPG hose length didn’t change). Lower the rig into the water off the boat or in a pool and don in the water.

Build a protector if you like it. If not, at least you will gain some experience and insights.

 

[Glenn08]

Akimbo; interesting posts. I especially liked the doubles with the two hose regulator - even though it wasn't valve-down.

 

[Tortuga68]

Yes you can fit protectors... or you can not fit protectors and mount them valve up

Why do you need protectors for ice diving? As opposed to any other overhead environment like cave or wreck, which most people these days don't use protectors for

I have a theory as to why scuba tanks are typically worn with the valve(s) behind the diver's head

So let's hear it then