Dual Yoke Crossover Bar

[Hoosier]

Dear all dive mania,



I am searching the way of two tanks configuration on Scubapro BC for recreational diving. Thanks to the board members, I got some ideas how to set up the double bands on Scubapro BC. So, my next search is about valve configuration on those two tanks. I am wondering if anyone is using dual yoke crossover bar (see the attachment) for two tanks configuration. It looks very versatile set up to change from single to double or vice versa without taking out the original valve for manifold.



Please let me know its pros and cons of this set up?

In addition, I found out that Sherwood has made this crossover bar, but I am not sure where to get it. Have you had any experience with www.alphadiving.com in Australia?



Thanks for your inputs in advance.

 

[Nemrod]

The cross over in the middle of the pic is probably no longer made. They worked fine for a temporary set up. They are suitable for open water recreational diving. I would not use it in a tech, cave, wreck or deeper than normal diving. Why, well, there is only one outlet, there are two more O-ring failure points, they are weaker and more easily damaged than a one piece of threaded type manifold.
Unfortunately, for whatever reasons, probably lawyers and lack of tort reform an lawsuits most of this equipment is no longer made or imported into the Peoples Republick of the USA. The dual outlet--outlet centered over the tanks, is still made from several sources, the older centered outlet and centered and RH outlet is not availabe and darn if I see any Y valves out there either. N

 

[DA Aquamaster]

You would be a lot better off with independent doubles than with using a crossover bar like that.

 

[jonnythan]

Why do you want to start using doubles? That will help us answer your question.

 

[Hoosier]

DA Aquamaster, Jonnythan, Scubaroo, Nemrod, and Walter.
I really appreciate for your inputs so far.

As you may guess, I don’t plan to dive into the technical diving area. Yes, you can call me “You are a newbie.” but I am trying and I am learning step by step

There are a few goals that I am pursuing for:
1. Max. utilization in the current gear: What I want is to utilize my gears that I have already had without having additional gear at this moment so I have already asked the question about compatibility of tank bands on Scubapro BC in other thread.

2. More bottom time within a recreational diving depth (< 60 ft).
3. Versatility: It looks easy to change either single or double tanks
4. Limited budget: It is always an issue.
5. Travel: Whenever I go, I can make a double rental tank in a second without hassling with LDS.
6. Less gear on dive: I am using Air 2 and wrist computer with transmitter that I have been waiting for.

For this configuration, I am considering to have the following ones:
1. SS twin tank bands (DIY from “Walter” or Aqua Explorers bands)
2. Twin tank boots
(http://www.beaverscuba.co.uk/catalogue/cylinders&accessories/cylinders&accessories.htm)

I am still listening to any suggestions.

Thank you!

 

[jonnythan]

The big problem with the yoke crossover bar you mentioned is that in the event of basically any failure in the air delivery system, you can lose all your gas. For instance, if any of the main yoke O-rings (the ones on the tanks as well as the one in the center), a first stage malfunction that results in a freeflow, a second stage O-ring blowing that results in freeflow, etc, you either turn off your only gas supply or lose all your gas. If you're into computers, it's kind of like RAID 0 vs RAID 1. You're *increasing* potential for catastrophic failure, not *decreasing*.

If you dive independent doubles or manifolded doubles you have two first stages which you can shut down independently. This allows you to isolate any gas loss problem. DIN O-ring blows? Shut down the post and still have all of your gas. Primary second stage hose blows? Shut down the post it's on and still have all of your gas. Tank blows its valve O-ring? Shut down the isolator in the center and still have everything in the other tank.

You should be looking for ways to minimize catastrophic failure potential when doubling up tanks. That's one of the big benefits.. you always have redundant gas in the case of almost any failure. This system would be *less* reliable than a single tank. More gas, but more failure modes and more potential for failure.

 

[JS1scuba]

The Crossover manifold that attaches two cylinders via the K valve is known as a "cheater bar" they were popular in the 70s and 80s for quick rigging a set of doubles and using a single regulator system. I had one in 1988 and used it for about 5 mos. It has issues that far and above make the unit a bit of a hazard. To make it work we ll you need to change the yoke nuts to real nuts and bolt it down to the valves and have a very secure set of bands on the tanks.

Suffice to say that the idea is good but the execution is not.

IF you want to fly twin tanks on a scuba pro stab jacket that can be done by using twin tank bands that have hoops on them (convex bow) that cant fit into the concave shape of the SCP back pack and then bolt them on, but be sure you have a proper dual outlet manifold on the tanks.

An alternative to this "hard band/manifold" set up is to use the AquaExplorer Velcro bands -- these were originally designed to fit into the Scuba Pro back pack and allow you to snug up two independant cylinders and dive them as doubles. (single 80 with an 80 cube pony)

the link to find these is http://www.aquaexplorers.com/double_bands.htm

and an image is below --- you will see the "plate" is convex to allow a nice fit with the SP back pack.

I used these in the ealier model (injection molded plastic) for years and always love them. Once I went on to more serious work i needed manifolded doubles, but for travel these are great.

Some may scoff at the 'independant doubles" set up but suffice to say you learn really good gas managment when you use these. Its not any different than "side mounting" for cave diving. When I was using these I would breathe down a cylinder in 500 psi increments. 3000-2500 --switch -- 3000-2500 switch, 2500-2000 switch 2500-2000 switch ... 2000-1500 switch .. 2000-1500 switch . 1500 on up and out

It's all in the management.

Regards,

 

[DA Aquamaster]

A cheater bar will not really work with a set of travel bands as they will not be rigid enough and it will cause problems.

I share your desire to have flexibility and to have a configuration that is ammenable to travel and use of rental tanks. With independent doubles, I can use one tank during a recreational dive with the other along as a really large pony and on a second rec dive I can then use the second tank with the 500-700 psi reserve in the first tank as a "pony". Alternatively I can do deep and or longer doubles dives by using both tanks. Normally you breath the first tank down 1/3 then switch regs and breath the second tank down 2/3rds leaving a 1/3 reserve in each tank.

So my advice would be to pick up the travel bands and spend just a bit more money on another first and second stage rather than on a cheater bar.

I like the Aqua Explorer bands as they are duerable, fairly low profile, relatively rigid for a travel band and are easy to change tanks. They also have the benefit of being useable on a normal BC using the curved adapter or, with this adapter removed, on a backplate and wing.

 

[kman458]

A cheater bar will not really work with a set of travel bands as they will not be rigid enough and it will cause problems.

I share your desire to have flexibility and to have a configuration that is ammenable to travel and use of rental tanks. With independent doubles, I can use one tank during a recreational dive with the other along as a really large pony and on a second rec dive I can then use the second tank with the 500-700 psi reserve in the first tank as a "pony". Alternatively I can do deep and or longer doubles dives by using both tanks. Normally you breath the first tank down 1/3 then switch regs and breath the second tank down 2/3rds leaving a 1/3 reserve in each tank.

So my advice would be to pick up the travel bands and spend just a bit more money on another first and second stage rather than on a cheater bar.

I like the Aqua Explorer bands as they are duerable, fairly low profile, relatively rigid for a travel band and are easy to change tanks. They also have the benefit of being useable on a normal BC using the curved adapter or, with this adapter removed, on a backplate and wing.

i am also looking to do something like this for travel. my question is i dive with a computer and since the tanks are independent how will that affect how the puter reads nitrogen load, bottom time, and ndls as you will not be breathing off the tank with the puter the whole dive. i also had someone tell me to get 2 reg set ups like you would use for a set of independents and a high pressure hose and connect a high pressure port from each first stage together to equalize the tanks and use one second stage as a primary and the second as an octo. it did not sound good to me but i really did not have a good reason to tell him why it could not be done.

 

[DA Aquamaster]

i am also looking to do something like this for travel. my question is i dive with a computer and since the tanks are independent how will that affect how the puter reads nitrogen load, bottom time, and ndls as you will not be breathing off the tank with the puter the whole dive.

On a recreational dive where you are essentially diving using a single tank by only using one of the 2 tanks, an air integrated computer works normally as it does not know the other tank is even along for the ride since you are not using it.

If you are diving on deeper and longer dives using both tanks, the AI function will get confused when you stop breathing from the tank with the computer on it. But to be honest, if you are doing deeper and longer dives with doubles, you shoud not be relying on an air integrated computer anyway as it will eventually get you in trouble.

Normally, a dive computer's computation of nitrogen loading and NDL's is not affected
by the rate of air consumption. The exception here is some Uwatec (and possibly other) air integrated computers that adjust the rate of N2 loading based on workload as measured by air consumption. With one of these computers the N2 loading would default to some minimum value. But I dont think this would be a problem as I think that the increase due to consumption is just adding a saftey factor over the regular algorithm and reduced air consumption won't reduce the computed N2 loading below that point. But you would really need to read your computer manual to determine this.

I also had someone tell me to get 2 reg set ups like you would use for a set of independents and a high pressure hose and connect a high pressure port from each first stage together to equalize the tanks and use one second stage as a primary and the second as an octo. it did not sound good to me but i really did not have a good reason to tell him why it could not be done.

Your instincts that it is a bad idea are correct. This seems to be a variation on the idea used by one manufacturer to use the primary tank to keep the pony tank topped off. But without the neccesary check valves in the system it would leave a set of independent doubles less than fully independent.

The flow rate through most high pressure ports is restricted to a very small orifice. This would on one hand limit the amount of equalization that could occur and could leave you with a very misleading impression of how much air is really left if you or your computer is reading the SPG on the tank that you are not currently breathing out of if you are at depth and breathing air from the other tank substantially faster than it can transfer from the tank with the SPG. On the other hand, if you experience a regulator failure and shut off a tank valve, gas will still transfer from the other reg to the one that is malfunctioning. The malfunctioning reg will not really care whether the air in the HP section is being fed from the tank or through the HP port. The flow rate will be reduced, but if the reg is freeflowing, gas loss will still occur.

So in short, I see no advantage with doing it this way and all it really accomplishes is compromising the integrity of an isolated redundant air system.

For gas management with independent doubles you need an SPG of some sort on each tank. I normally have an air integrated computer on the right tank and use it exclusively on recreational "single tank" dives. I have a regular SPG on the left tank and use it along with the SPG in the air integraed computer (often in gauge mode) for air management when using both tanks.

For streamling/hose routing purposes I cross the HP hoses over with the right tank going to the left side and vice versa. It sounds potentially confusing in the event of a failure and the need to shut off a tank but it really isn't as you quickly become very familiar with what goes where. With proper gas planning and management there really is not need to shut off a tank valve in the vent of a reg failure as you will have adequate gas in the other tank to finish the dive. It is however a very good idea to shut off the offending tank as you can never have too much gas. To facilitate this I reverse the orientation of the left tank so that the tank valve knob is on the outside where it would be on a set of manifolded doubles. It makes it much easier to reach but does draw comments from people who think you are assembling things backwards.