Possible tank band problem

[Beau640]

Hey guys

I'm putting together a second set of doubles for myself and my new tank bands came in. Putting them on, the bottom ones sit nice and flush all the way around and look great. The top ones though look a little off (see pictures below). Theres a small gap between the bands and the tank almost like the tanks are just not quite right in there. Although no matter if i tighten them more, loosen them, or try to shift them around they always look like that. I've measure them from every point and they are even on the tanks, and the manifold still has play and appears threaded completely evenly. If i slide these top tank bands all the way down to the bottom where the other tank bands are, they have less of a gap but still a tiny one. I'm wondering if these new tank bands are warped? Or is this normal and okay? Comparing these to the other set of doubles I have there's no gap in the top or bottom bands so I didn't know if this was normal or not for some bands.

Thanks

 

[lowviz]

Call them up, get an RMA number, then send them back for a replacement set.

One of the loops is larger than the other. They will never be right. Make sure that the tanks are parallel when both bands are in place and tightened.

 

[rx7diver]

I'm putting together a second set of doubles...

Beau640,

Your photos don't show your manifold. I am wondering if your manifold spacing is too wide. If the spacing is too wide, then if you tighten the bottom band (while the top band is loose), your tanks will "keystone", which will make the top band seem too big.

First thing you might try is: Remove both bands, and then set them atop one another to see if they in fact are of the same dimension/size. If they are, then maybe you need to *decrease* the center-to-center spacing of your manifold--if this is even possible. I have an old style OMS 300 Br manifold (has face O-rings, rather than barrel O-rings, for the isolator part), and I have one of the original Sherwood Genesis Double-DIN manifolds. Neither of these manifolds can have its center-to-center spacing changed.

Hope this helps.

Safe Diving,

rx7diver

 

[rjack321]

If i slide these top tank bands all the way down to the bottom where the other tank bands are, they have less of a gap but still a tiny one.

This indicates that the tanks are not parallel. The manifold is pushing the tops apart. The manifold "seems fine" because the threads on the cross bar are so fine almost any misalignment won't be noticed.

Lay the tanks on a perfectly flat table
Loosen both bands
Get the top band bolt snug but not tight
Tighten the cross bar while you alternately tighten the top bolt
Once the top bolt and crossbar are close to final then snug up the bottom bolt

 

[halocline]

I'm not totally clear on what's wrong. In the 2nd pic it looks like the top band is tighter around one tank than the other, which would indicate that either the two tank loops in the top band are unequal length or the tanks are unequal diameter at the top. Is that what you're worried about, or is it that the top band is generally looser than the bottom band?

Anyhow, you could try taking the top band off, flipping it over so that the loops are on the opposite tanks, try again. If it's loose around the same tank then you know the problem is not with the band.

You could try switching bands so that the top one goes on the bottom, see if that fits better. You could also try installing and tightening the bands without the manifold in place just to see how that fits. That would let you know if there's a problem with these bands.

I have found that its a bit of a compromise on my doubles to get the manifold freely rotating with the bands tight and the isolator valve pointing up. With my blue steel manifold, there's about a 1/4 turn play when the bands are tight. Most of the times I put them together (they come apart for VIS every year) it seems that play happens with the iso knob pointing any way but up.

 

[divad]

What he said....also, do you know we can see your foot?

 

[Beau640]

I had contacted dive gear express about these bands since that is who I bought them from. Been working with them to try to figure out what the problem is. Finally came to the solution of backing off the manifold by about a turn and a half to two turns. After doing that and retightening the bands the tanks now are the proper length apart to completely fill out the bands appropriately. Everything is level perfect and rock stable now.

For whatever reason this crossbar went completely threaded pulled the tanks a little too close together so that the bands didn't fit properly. Haven't run into that problem before since usually threading it all the way and then backing off a quarter turn so the valve is in the proper position places the tanks the correct distance apart.

Glad it's fixed thanks for the replies and thanks to dive gear express for all the emails today to come up with a solution

 

[rjack321]

Glad you got it sorted out. I could tell they weren't parallel; a bit surprised you had to push the tops apart but I guess that's the optical illusion of perspective photos!

 

[halocline]

Oh, I think I see. You need to tighten the bands and adjust the manifold at the same time, constantly adjusting the manifold to keep it from binding as you tighten the bands. As you tighten the bands, the tanks can move a little further apart, because the flanges get pulled together.

 

[lowviz]

Oh, I think I see. You need to tighten the bands and adjust the manifold at the same time, constantly adjusting the manifold to keep it from binding as you tighten the bands. ...//...

Exactly, it is a dance. Small changes, everything in concert, tanks always remain parallel. The mistake I made in post #2 was that I didn't ask if the same gap was also seen when looking up from the bottom. We all learn...