Anybody know how manifolds work?

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Guys, here in the bottom of the Philippines we had a great number of spearfishermen wanting to stay down longer so they went for twin tanks. Not wanting to spend more money on another reg they use a device like this. I will try to describe it. Imagine a yoke 1st stage. Now imagine them on either side of a 6 inch metal pipe. Then in the middle of the pipe is a post where you connect your reg. You band two tanks together facing each other. No redundancy, more failure points. But this setup allows for you to rent single tanks and get more air for the dive. I saw one two weeks ago and was surprised to find the thingy was made by Dacor. Im sure it was a long time ago. My question is where does this fit on the timeline and do they still make these?
 
Locally we called them pig tails and cheater bars. Pig tails used a pig tail looking sort of loop on one side to allow some adjustability and flexibility to accomodate tank and band arrangements with different centers and to accommodate less than solid band arrangements wher some flexing may occur. They were I believe a pretty early design and I have seen US Divers models with flat chrome finishes that would date them from from the 50's or early 60's.

Cheater bars used a solid tube arrangement between the yokes and were designed to be used with tanks and bands with specified center to center measurements. Earlier ones used metal thumb screws on the yokes while the last ones I saw (sold by Dacor anda couple other companies in the mid to late eighties) used hex headed bolts for more security.

They worked ok as long as the tanks were properly aligned and secured properly in a decent set of bands (an awful lot of "ifs" involved) but they were by no means as secure as a regular doubles manifold.

Since they attached to a pair of regular K or J valves, they did allow you to shut off either tank and use a J valve reserve on one or both tanks. The ability to shut off each tank individually did protect you from a blown neck O-ring or burst disk failure but you still had only one reg and you had a total of 3 yoke connections to potentially fail.

They did save you the cost of buying another regulator which would have been required to go the independent doubles route. But that was the only "advantage" as they offerred no operational advantage, provided less redundancy and posed more potential failure points.

One of the big changes over time was that in the 50's, 60's and even early 70's all you needed was a tank with a J valve, a regulator and maybe a relatively inexpensive horse collar or even a surplus mae west to go diving. (no SPG, no stab jacket, no computer - maybe a cheap capillary depth gauge)

So the regulator was the spendiest piece of equipment and the cost of the regulator was a significant portion of the total equipment package. So using another regulator (on a pony bottle or a set of doubles) represented a very large investment and was not something most divers considered. Consequently single outlet manifolds of various types that would require only one regulator were the standard of the day even when single hose regs became common.
 
I remember my Dad made his own bar out of brass on the lathe to manifold two steel 38's, probably about 1972. Made his own Hawiian Pack to hold them, with a piece of lead screwed to the pack for trim.
 
So in a practical note... it sounds like the manifold is between the tank and the tank valve (where 1st stage connects? Is that correct?

To me it would make since that’s IF you shutdown a tank air should not leave the tank?

I have my first set of steel doubles and I am going to split them into sidemount singles. When I loosen the manifold nuts the tanks blow air. I have the nuts to cap the manifold so I am left with a right and left valve. However if I have to drain the tanks my LDS will likely charge me for a VIS again. They were just VIS last month.

Valve is old OMS manifold.
 
Here is a cutaway photo of an isolation manifold.
upload_2017-11-22_17-0-48.png


XS Scuba Isolation Manifold
 
Thanks. But why not block flow if tank is closed?

Cylinder stop valves don't offer as much flexibility as regulator port stop valves. Here is a schematic diagram:

full.jpg


The purpose of the "post" valves is to isolate a failed (free flowing or failed O-ring) regulator . The isolation valve is to isolate failed cylinders (cylinder O-ring or blow out plug). The concept is to allow either regulator to use what onboard gas is available. Does that make sense?
 
The goal of the value on the tank to shut off the flow of gas to the regulator.

The goal of the isolator is to shut off the flow of gas between the cylinders.

Scenario A. A regulator on one post goes tits up, you shut down that post and you have full access to all of your gas.

Scenario B. A value on one post goes tits up, you shut down the isolator to maintain gas in the other cylinder.

If the valve blocked the flow of gas at the "cylinder" level as you would like in Scenario A you would lose access to the remaining half of your gas. In Scenario B there is no difference.
 
So in a practical note... it sounds like the manifold is between the tank and the tank valve (where 1st stage connects? Is that correct?

To me it would make since that’s IF you shutdown a tank air should not leave the tank?

I have my first set of steel doubles and I am going to split them into sidemount singles. When I loosen the manifold nuts the tanks blow air. I have the nuts to cap the manifold so I am left with a right and left valve. However if I have to drain the tanks my LDS will likely charge me for a VIS again. They were just VIS last month.

Valve is old OMS manifold.

Tell your shop what your doing in advance. Or try and borrow a tranfill whip to partially fill your tanks after you split them up.
 
https://www.shearwater.com/products/swift/

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