Bands-manifold mismatch?

[AbyssalPlains]

Hi all,

Bought a used set of Faber LP95s. Took it apart since the tanks needed hydro. The o-rings in the crossbar looked fine but they are square in profile. Should they be round? Problem is, there seems to be an issue with the spacing. When everything is assembled, the tanks are closer at the bottom than at the top. Even when the crossbar is at its shortest usable distance. The only way to align everything perfectly is to screw in the crossbar all the way on both sides, but then the isolator valve ends up in an unreachable position. I put everything together slowly and without tightening anything. I noticed the cross bar turned very easily at first, but then became harder to turn toward the final position. I nudged the tanks until I felt any tension was gone, but crossbar was still a bit hard to turn. I tightened the bands before tightening the cross bar, but when I filled the tanks, air started leaking from the crossbar. I adjusted the jam nuts on the crossbar back and forth a little with tanks under pressure (~500 psi) and the leak stopped.

Should the tanks be perfectly parallel? If yes, I wonder if I have the wrong bands. I didn't know they came in different spacings. The original owner didn't know the manufacturer of the bands. They seem well-made but have no markings of any kind. What should I do? Take the rig to the pool and see how it works? Order different bands? But how do I know which ones? The manifold is a 3000psi Thermo.

I should mention that I lined the insides of the bands with duct tape. Just one layer, though. I can't imagine that to throw things off.

 

[rjack321]

The tanks need to be perfectly parallel (plus-minus maybe a millimeter). You can measure with a ruler outside, inside to outside, or with calipers. If not you are bending the manifold which is very bad. Its not meant to have lateral stresses on it as evidenced by the leaks.

Given all the problems you are having with these tanks, bands, and valves, I would drain them ASAP. Then take the whole mess over to Joel at TDL in Havansu. He is a Thermo dealer. He can check the post hydro flash rusting, check the bands, and check for manifold damage. Then help you set this stuff up right in person - with the correct O-rings.

This is life support stuff. You want it done right not some crazy half-arsed thing from before or picked up off the interets - either of which can either kill you UW or the fill station operator.

 

[AbyssalPlains]

Alright - I drained the tanks and loosened the bands. Looking at them again, I realized that what I thought was them being closer together at the bottom is in fact part of the shape of the tanks. Apparently, the Fabers bulge out a bit on the bottom, so the gap is smaller at the bottom compared to the top when doubled up. Looking at their alignment in the mid section, between the bands, they do look parallel. Of course, I could only eye-ball it for now, until I get a better measurement.

I do like the suggestion of getting Joel's advice - in fact, I am going to Lake Mojave in a couple of weeks, so I think I should be able to swing by TDL on the way up there.

Thanks!

 

[ajduplessis]

Assembling doubles should not be a painful job. It is difficult to understand what you have equipment wise and how you proceed to assemble them. A couple of things do come to mind:

- The manifold/cross bar should turn freely during the entire process. I don't tighten the bands completely at first. Screw in the manifold a turn or 2. Then tighten the bands a couple of turn, the manifold should turn freely. If this is not the case loosen the bands a bit. Keep repeating the process to completion.
- Do you have the correct bands for the tanks? Do you have the correct length manifold for the bands/tanks? If the manifold screws in all the way, they are to long IMO. This could explain the sqaure profile on them, they are forced into that shape in the back of the pilar valve when turned in all the way
- I have fabers and they don't bulge. They are very straight.
- Take them to the TDL boys, they will sort you out quick.

 

[AbyssalPlains]

Assembling doubles should not be a painful job. It is difficult to understand what you have equipment wise and how you proceed to assemble them. A couple of things do come to mind:

- The manifold/cross bar should turn freely during the entire process. I don't tighten the bands completely at first. Screw in the manifold a turn or 2. Then tighten the bands a couple of turn, the manifold should turn freely. If this is not the case loosen the bands a bit. Keep repeating the process to completion.
- Do you have the correct bands for the tanks? Do you have the correct length manifold for the bands/tanks? If the manifold screws in all the way, they are to long IMO. This could explain the sqaure profile on them, they are forced into that shape in the back of the pilar valve when turned in all the way
- I have fabers and they don't bulge. They are very straight.
- Take them to the TDL boys, they will sort you out quick.

Thank you so much for these tips. That is exactly the kind of info I was looking for. In the meantime, I realized the tanks don't bulge, it just looked that way. From what you say it seems I do have the wrong manifold for the bands, which sucks. I bought the whole set used. I knew that it was put together by a dive shop and it looked in great condition, so I didn't think there could be anything wrong with the parts. Now I'm questioning whether that dive shop knew what they were doing. They went under a couple of years ago, but that probably doesn't have anything to do with it...

It does look like the manifold might be too long, unless that one layer of duct tape lining the bands makes enough of a difference (as it pushes the tanks closer together due to its thickness), but I have a hard time it could be that much, something like a hundredth of an inch...

In terms of technical diving, this is a real bad location. That is why I'm having so much trouble doing things right. There is nobody in a 100-mile radius to show me. None of the three dive shops in my city has ever assembled a set of doubles. They know everything about recreational equipment and Aluminum 80s, but there is nobody with a thorough knowledge of technical equipment.

If I had known this would be so much trouble, I would have just a bought a brand-new set of doubles. If I indeed have to buy another manifold, I will have spent pretty much the same amount of money.

I'm going to give Joel a call today.

 

[rjack321]

From what you say it seems I do have the wrong manifold for the bands

Maybe. I suspect the bands might be old/dated but the manifold is relatively new(?).

In terms of technical diving, this is a real bad location. That is why I'm having so much trouble doing things right. There is nobody in a 100-mile radius to show me. None of the three dive shops in my city has ever assembled a set of doubles. They know everything about recreational equipment and Aluminum 80s, but there is nobody with a thorough knowledge of technical equipment.

If I had known this would be so much trouble, I would have just a bought a brand-new set of doubles. If I indeed have to buy another manifold, I will have spent pretty much the same amount of money.

I'm going to give Joel a call today.

I am guessing that Joel will only have to show you this stuff once so it will be worth the drive to learn how its all "supposed" to work. Its not that complicated IF the bands and manifold aren't mismatched. The best way to figure out if its "you" or the components is to show everything to someone who's dealt with it before.

You could post a zillion pics here and various people could probably help, but in-person with bands/tanks/manifold in hand will be much faster and more confidence inspiring.

 

[TSandM]

You might PM AztekDiver or Karen Cleveland and ask them if there is someone in the Phoenix area who could take a look at the tanks for you. Not exactly local, but Tucson to Phoenix isn't a bad drive.

 

[Leadking]

It would be hard to imagine that the bottoms of the tanks would be larger. The manufacturing process is by "deep draw" in which a round disc of metal is pushed through a round ring. This is done three or four times, lengthening the cylinder each time. if the bottom was larger than the top it could not be ejected from the die.

 

[AbyssalPlains]

It would be hard to imagine that the bottoms of the tanks would be larger. The manufacturing process is by "deep draw" in which a round disc of metal is pushed through a round ring. This is done three or four times, lengthening the cylinder each time. if the bottom was larger than the top it could not be ejected from the die.

Yeah, that was my ignorance talking. It just looked that way but I checked with a straight edge and realized it was an optical illusion. Live and learn.

 

[halocline]

You need 8" bands for the LP95s. If you have those and a standard adjustable manifold, you'll be fine. There are decent videos on how to do it, I think scubatoys had one for a while. The trick is to get the crossbar started evenly on both sides, then tighten the bands and shorten the crossbar back and forth, making sure the crossbar is always free to move. I have taken apart doubles for inspection, put them back together with the same bands and manifold, and had to futz with them annoyingly to get the iso valve to freely point up when everything was tightened. It's just a bit of a pain, but you'll get it. I'd take the duct tape off, BTW. Just remember to do get the crossbar started evenly in both valves, then a turn on the bands, one on the crossbar, etc....

Don't listen to this "life support" crap. You're not going to kill yourself or anyone else. If you screw up, your tanks will leak and you might bend or damage the manifold. Hardly life or death.