spacing between tank bands/tanks?

[Spoon]

guys just installed my manifolds and tank bands on my tanks. perfect fit my only concern is that the spacing at the lower part of the tanks is narrower than the top part. its not noticeable or anything but i saw it. their seems to be no stress on the manifolds and the tanks seem to be carrying the weight fine? this ok?

also when lifting them tanks is it ok if i carry the tanks from the base and tank bands leaving the manifolds hands free?

my first twins rig so excited to test!

[GreenDiverDown]

Your cylinders should be parallel. If I understand what you are describing, then something ain't right.

What manifold did you get? Bands? Cylinders? Of course, these shouldn't matter, but it will help me get an idea of how you put things together.

[GreenDiverDown]

also when lifting them tanks is it ok if i carry the tanks from the base and tank bands leaving the manifolds hands free?

my first twins rig so excited to test!

I was taught to carry them from the base and shoulder.

[wb416]

guys just installed my manifolds and tank bands on my tanks. perfect fit my only concern is that the spacing at the lower part of the tanks is narrower than the top part. its not noticeable or anything but i saw it. their seems to be no stress on the manifolds and the tanks seem to be carrying the weight fine? this ok?

also when lifting them tanks is it ok if i carry the tanks from the base and tank bands leaving the manifolds hands free?

my first twins rig so excited to test!

when they screwed the manifold together, they didn't square up the top and bottom of the cylinders as the bands were being put on. With the top nuts on the isolator bar loose, the isolator should fairly easily turn forward and back (toward and away from your head). If it doesn't, the manifold is in a bind.

I carry my tanks by grabbing around the base of the valves and doing a "pullup" toward my chin. I've seen many (especially women) that will squat and put one arm around the top right side of the cylinders and the other hand/arm under the bottom left side and stand up..... this is more technique and less raw arm strength... and a lesson that many of the guys could learn so that we have longevity in diving and forego unnecessary lifting injuries!! :D

[GreenDiverDown]

my first twins rig so excited to test!

...hope you kept your SS BP

[Spoon]

Your cylinders should be parallel. If I understand what you are describing, then something ain't right.

What manifold did you get? Bands? Cylinders? Of course, thses shouldn't matter, but it will help me get an idea of how you put things together.

luxfer alum 80's with halcyon 300 bar manifold and highland millworks bands

[GreenDiverDown]

I would re-do 'em.

Did you put anything under the bands?
Did you put them together with them flat on a table alternating turns of the cross bar with gentle taps at the base of the cylinders?
Were you sure to not overtighten the bands... ie no dimpling?
After you tightened the bands down were you still able to roll the cross bar 180 degrees?

The sides of the cylinders should definitely be parellel. It's not unusual, however, for twins to not perfectly sit upright... without a little wobble, that is. Cylinders aren't EXACT duplicates. There is some variation. Still, the sides should be straight and when doubled up these sides should be parallel.

[Mark Vlahos]

guys just installed my manifolds and tank bands on my tanks. perfect fit my only concern is that the spacing at the lower part of the tanks is narrower than the top part. its not noticeable or anything but i saw it. their seems to be no stress on the manifolds and the tanks seem to be carrying the weight fine? this ok?

also when lifting them tanks is it ok if i carry the tanks from the base and tank bands leaving the manifolds hands free?

my first twins rig so excited to test!

A few points here.

The tanks should be absolutely parallel.

The bands should be tight, but not so tight that the flat parts where the bolts are get deformed, but still pretty darn tight.

The crossbar or isolator on your manifold should be able to turn without too much effort before you tighten the nuts locking it into position. The isolator or crossbar should be as close to perfectly centered between the two valves as possible.

Assembling the entire system is much easier if you have a sturdy flat table where you can lay the tanks and slide them around. The process of tightening everything is a lot of... Tighten the upper bolt a little. Then tighten the lower bolt a little. Then check the mainfold and adjust a little. Then go back to the bolts. Then back to the manifold. To really get it right takes some time, and you need to be very willing to take it all apart and start over if things don't look just right.

When you are finished the tanks should be parallel, the isolator needs to be free to move before you tighten it into position with the nuts, the isolator valve should be tilted a bit toward the back of your head to make the valve a little easier to reach.

At least in the United States the standard center distance for the bolts is 11 inches, and precisely 11 inches. Many backplates now have a short slot for the bottom bolt, some plates do not. Even if you have a slot you should try to get the standard spacing because you might in the future use a different plate for one or two dives, and it would suck to need to re-adjust the spacing.

Speaking of adjusting the doubles, be extremely cautious if you try to adjust the tanks when pressurized. Never loosen both bands on pressurized tanks, doing so invites damage or failure of the manifold. If you get it right the first time you should not need to adjust them, but heck we live in the real world, so be really careful.

For carrying the tanks try pointing the bolts away from you with the cylinders standing upright. Now put your left hand on the outside of the left hand valve (not between the cylinders at all) and put your right hand between the cylinders at the base and with your palm toward the base of the right hand cylinder lift them up so the valves are more or less pointed toward your left bicep and the bottoms of the cylinders are pointed toward your right hip. The end result is that the cylinders are somewhat diagonal accross your abdomen. You can also carry them by putting your hands on the valves atop each cylinder, just be careful to never lift them by the center of the isolator. This is a very tempting place to carry the cylinders from but it may damage your manifold if it gets bent. Always be careful not to hurt your back when carrying doubles. If you need to carry them very far either get some wheels or attach them to your back plate and wear them.

Enjoy the doubles, but now you really need to keep an eye on your bottom time since air will not be a limiting factor.

Mark Vlahos

[PhilEllis]

luxfer alum 80's with halcyon 300 bar manifold and highland millworks bands

If you have the correct Highland bands, it is VERY hard to set the doubles up incorrectly. I have a suspicion that you might have the wrong Highland bands. A flat table, correct bands, properly working manifold makes this a simple assembly. DO NOT DIVE THEM if the distance at the top and bottom is different. This will eventually lead to trouble in the manifold. Thanks.

Phil Ellis
Dive Sports Online
www.divesports.com
(800) 601-DIVE

[Spoon]

...hope you kept your SS BP


yup kept em

[Spoon]

Did you put anything under the bands?
Did you put them together with them flat on a table alternating turns of the cross bar


i put some rubber inner tubing on the tanks, about as wide as the bands to prevent the metals from touching each other. i also installed them while the tanks were upright.

[GreenDiverDown]

yup kept em
Good deal!

So... have you had a chance to look at the problem again. What's up?

[Spoon]

Good deal!

So... have you had a chance to look at the problem again. What's up?


im actually going to try solve the problem in a bit. i will try loosening the bands a bit and see if i can get em straightened out by tightening the manifold more. i tighten it enough, i reckon i still have one or two more full revolutions to spare that should straighten out the tanks. il be back in a bit.

[GreenDiverDown]

i put some rubber inner tubing on the tanks, about as wide as the bands to prevent the metals from touching each other. i also installed them while the tanks were upright.

We're out of synch... :D

If things still look off, then I would say re-assemble it. But this time do it with 'em flat on a table. Mark described it pretty well. I looked for a couple of web pages that showed exactly how to do this but the links are dead. One was on the Diverite site and the other was cisatlantic. Maybe someone knows where they went.

I know people have different thoughts on this... but... I would suggest that you loose the rubber. I have done it both ways and it seems to me that the corrosion that takes place is so superficial that it would take many, many years for it to cause a hydro/vis inspection failure. IMHO, it just isn't worth the worry or the risk of a bad double-up.

But I do remember what it's like getting one's first set... ya kinda want to baby 'em... they look so good and all.

If you can't resist the urge to put something under the bands, then I would suggest that you use something besides rubber. I've found two things that work really well. the first is the plastic... or whatever material... of a bleach jug. (Get the biggest diameter bottle that you can find.) It is pretty thin, won't degrade like the rubber, and is easy to work with.

The second thing is even better but it might be a little hard to find. I'm talking about the tint liner that some stores put on their windows. It is even thinner than the plastic of a bleach bottle and it has one side that is sticky. It works great. You just put the sticky side against the inside of the bands. This makes getting everything in the right place much easier because the protective layer moves with the bands as they are tweaked into just the right place. If you can't find any of this stuff, I've got plenty and I'll send you some if you want. The dark color is nice, too.

What ever material you use, remember to cut it so that it will extend past the width of the bands about a 1/4" or so on each side or you'll still get corrosion.

I have some pics of how to do this if you would like to see them.

Still, my best advice is to not put anything under the bands. Don't worry... soon you will forget about it. The first time that you have to take 'em down for a vis you'll probably think, "yuk". But then you'll slap the bands back on and soon forget about it.

One more thing... no matter what you put under there, you're still gonna get some dissimilar metal reaction. There's no getting around it.

[GreenDiverDown]

Oh... I found one...
http://www.diverite.com/TecTalk/doubles/index.htm

[GreenDiverDown]

Here are the pics.

The first shows the two materials. The white stuff was cut from the wall of a Clorox bottle. The other stuff is the tint material. This is a little thicker than what they use on car windows.

The second and third pics show the tint material stuck on the inside of the bands. Note that the tint material is cut a little bit wider than the bands.

The fourth pic shows the white Clorox bottle plastic under the bands on a set of Al80's.

[Spoon]

taking em to the shop now, i could have gotten the wrong bands, justtried tightening the manifolds to try to get the top part of the tanks to line up together but the gap at the bottom of the tanks actually tightened up and made things worse.

[GreenDiverDown]

Hey... I found Jim Cobb's notes on this. Some of the pics are missing but it's better than nada.

http://web.archive.org/web/20040722080220/www.cisatlantic.com/trimix/doubles/doubles.htm

[Hoosier]

Those are the exact sites that I refer for the double set up. I doubled up two sets and it is just piece of cake... Just time consuming...

It is an interesting idea to use a tint film. I think the film can be purchased any glass shop. Many constructors used to install the tint film.

However, It isn't too thin for the band? I used the rubber bands from the www.reefscuba.com though.

[Spoon]

havent gotten my problem solved, the bands are perfect fit a;sp recpmfigured them with my buds many times in the shop. actually looks like one of the is the problem. one tank is straight but the other one isnt. i also checked the spaces between the valves and manifolds. one of em was off so had to rotate one of the tanks to get em even. dint help. tnaks are upright perfectly and are balanced. darn that gap!

[GreenDiverDown]

havent gotten my problem solved, the bands are perfect fit a;sp recpmfigured them with my buds many times in the shop. actually looks like one of the is the problem. one tank is straight but the other one isnt. i also checked the spaces between the valves and manifolds. one of em was off so had to rotate one of the tanks to get em even. dint help. tnaks are upright perfectly and are balanced. darn that gap!

You gotta re-type that. I have no idea what you're trying to say.

[Spoon]

You gotta re-type that. I have no idea what you're trying to say.

did the steps many times. the manifolds each engaged the valves at exactly the same time and as the manifold got tighter into the valves, the lower part of the TANK (right tank ) would get closer to the left tank. the left tank did not move at all. so the tanks were already misaligned towards the bottom. as i tightened up the bands, the right tank got even closer to the other tank.

two fingers fit perfectly with just a millimeter or so to spare on the top parts of the tanks while at the bottom i could fit the same two fingers but very very tightly. i reckon the bottom part is narrower by 1cm. according to the guy in the shop the problem may be with the bands but hes had several sets just like this and their is no stress on the manifolds as the bands seems to be bearing the brunt.

[GreenDiverDown]

according to the guy in the shop the problem may be with the bands but hes had several sets just like this and their is no stress on the manifolds as the bands seems to be bearing the brunt.

Hmm... I don't like it.

Take a look at the two links that I provided. They are the best descriptions of how to do this that I know. Then give it another go. If it is still off, then I would get another set of bands. I don't know that that is where the problem lies, but without being there it's hard to say.

I think that I might try banding them together without the manifold. If they pull up parallel, then they might be O.K.

Definitely remove anything that you might have put under the bands.

Even better... call or email Highland. They are very responsive and helpful.

I sure wouldn't just leave it like you have described.

Also, you might want to post this over on TDS. There are some pretty smart dudes over there. Maybe one of 'em has run into this before.

[Spoon]

Hmm... I don't like it.

Take a look at the two links that I provided. They are the best descriptions of how to do this that I know. Then give it another go. If it is still off, then I would get another set of bands. I don't know that that is where the problem lies, but without being there it's hard to say.

I think that I might try banding them together without the manifold. If they pull up parallel, then they might be O.K.

Definitely remove anything that you might have put under the bands.

Even better... call or email Highland. They are very responsive and helpful.

I sure wouldn't just leave it like you have described.

Also, you might want to post this over on TDS. There are some pretty smart dudes over there. Maybe one of 'em has run into this before.


me and the guy worked all afternoon to rectify the situation. manifolds are fine wll i think they are. il figure em over the weekend when i empty my tanks. im so icthing to fix the problem. will have updates soon. thanks stephen!

[Spoon]

i have dismantled my tanks yesterday. i am still unable to get the bottoms lined up. i checked the bands and they are exactly the same size as the other bands in the shop. these bands are already installed on tanks and they all line up nicely.

il bring them to the shop tom. im suspecting the bands are the culprits though as i get them perfectly lined up when prior to the placing of the bands on the tanks. once i tighten up the bands, the bottom tanks move closer to each other while the top part remains the same.

[GreenDiverDown]

once i tighten up the bands, the bottom tanks move closer to each other while the top part remains the same.

I wonder if you are screwing the manifold in too far. You should have some threads exposed when you're done.

First get your manifold close to the right spot, then snug down the top bad... not too tight. Use a feeler gage to check the top and bottom of the band to make sure that it is on even all the way around the cylinders. If not, make adjustments by tapping it with a piece of wood. Then place your bottom band in position but don't tighten it down. Then rotate the manifold in and out. You will see that the tanks pivot on the top band. As the manifold tightens the space between the tanks at the bottom will increase. Adjust the manifold so that the tanks are pretty close to parallel before you tighten the bottom band. Use your plate to position the bottom band and use the feeler gage like you did with the top band. Then go back and tighten the top band. Again, when you're done the manifold should freely rotate a 1/4 to 1/2 a turn.

Upon reviewing Jim Cobbs notes on this I see where he says that you might not have to worry if the tanks aren't perfectly parallel, given that the manifolds are designed to "have a certain amount of give". I'd still try to get it as close as possible.

Let us know how it goes.

[Spoon]

Upon reviewing Jim Cobbs notes on this I see where he says that you might not have to worry if the tanks aren't perfectly parallel, given that the manifolds are designed to "have a certain amount of give". I'd still try to get it as close as possible.

Let us know how it goes.


thanks for the help stephen. im curious though how much of misalignment is acceptable. if mine is acceptable i wouldnt bother. il be taking it to the shop soon for one last try, if all fails then il just suck up the misalignment issue and hopen for the best

[Spoon]

finally solved the problem. i inspected everything at home and made some adjustments:

1.) upon further inspection i found out that the left tank manifold was not as engaged as the right. the space on the left was bigger so i independently rotated this tank ONE full revolution to get them exact. Voilla aligned.

2.) i then aligned tanks as best as i could and placed the bands tightening the bottom before doing the top. all in all they are much better than before although their is still a very, very minute difference at the bottom but i guess this is the tolerance jim cobbs mentioned.

anyway thanks stephen for taking the time to help me out. your instructions really helped! props to you bro.