Custom Cylinder Bands

[cool_hardware52]

The manifolds are adjustable so if set right there should not be any tension on them.

Manifolds aren't really adjustable for center center distance. They are adjustable for the relative position of the two tank valves and the Iso valve.

The reality is you will either bottom out the Iso bar if you want to narrow the C to C very much, and unport the inner most Oring (most Iso bars have a pair of "Captured" orings on each side of the bar) if you try to extend the C to C distance more than about 1 turn.

I've had Occassion to design and fabricate extensions for Iso Bars, i.e. a solid piece of brass with one male end and one female end that alllows ~12" (vs 8.46 / 215 mm) spacing. I discovered this lack of center to center distance issue when I reverse engineered 3 commercial manifolds. I contacted the engineers at one of the makers and they were quite specific about what "adjustable" means.

Noo doubt there are many "adjustables" that have been extended to the point where the inner barrel oring is noo longer sealing, and the redundant outer oring is doing the job, but that is not how the manifolds were designed to work. The reduced thread engagement and single oring makes for a much less robust assembly particularly if the tanks / manifold are disturbed.

This video details the issue, starting about 2:30.

Tobin

 

[Caveeagle]

The manifolds are adjustable so if set right there should not be any tension on them.

And... if you are using an older OMS manifold.. There is not any wiggle room. Your tanks need to be lined up to match the valve centers or you will have a big problem.

 

[guruboy]

if you want exactly 6.9" D and 2.5" W bands you will probably have to find a pair if Highland mills bands.

Otherwise get them custom made at a shop like you said.

Good luck.

 

[BenjaminS]

The manifolds are adjustable so if set right there should not be any tension on them.

What I mean is if after a long dive and I feel like I weigh 500 lbs, I waddle over to a bench and lay my doulbes down heavy. I don't want to have my home-made bands breaking on me. I want experience.

 

[guruboy]

Old AL80 bands used to be 1.5" wide and pretty flimsy in terms of sheet metal thickness. LP72 tanks are lighter than AL80s and modern bands are probably twice as thick.

Unless you plan on shrugging off your backplate and tanks while standing and dropping them to the ground, nothing is going to break.

 

[cool_hardware52]

And... if you are using an older OMS manifold.. There is not any wiggle room. Your tanks need to be lined up to match the valve centers or you will have a big problem.

Face seal manifolds are one set length, but "Adjustables" offer so little genuine adjustment that they too should be considered "fixed"

As an aside a little manifold history. As tanks got larger in diameter manifolds had to get longer. Minimum manifold length is one tank diameter + one center band bolt diameter. 6.9-7 inch tanks and 5/16 band bolts os almost exactly 185 mm, which oddly enough was once a common manifold center to center spacing. 185's won't work on 8" tanks with 3/8 bolts 8.375 = ~213mm. That's where 215 mm manifolds came from. Along the way we had 197mm (2x 7.25" dia tanks and up to 3/8 bolts) Cranking a 197 out to 215 is a sure way to end up with a single oring functioning on both ends of the ISO.

Tobin

 

[Killerflyingbugs]

Thanks for the info, learn something new every day.

 

[guruboy]

Why are you basing it on bolt diameter and not the width of the bolt plate (or whatever it's called)?

 

[oldschoolto]

Older bands just had the bolt and not the larger bolt plates we see today.. The manifold sets the tank spacing.. Not the bands...

Jim..

 

[cool_hardware52]

Why are you basing it on bolt diameter and not the width of the bolt plate (or whatever it's called)?

Because the bolt has to fit *between* the tanks. Put two tanks side by side, no bands, just tanks.

Q. How far apart are the tank necks?
A. One tank diameter apart.

Q. What if you need a bolt to pass between the tanks?
A. You need to move the tanks apart by at least the diameter of the bolt

Q. Now how far apart are the tanks?
A. One tank diameter + one bolt diameter.......

The center plates on a set of bands are not located at the center line of the cylinders, but are spaced apart from each other. One could build bands with exactly the same center to center distance for exactly the same cylinders using different width (side to side) center plates. As the plates get wider they will also be further apart, front to back.


Tobin