Double 45's, super tight bands issue

[tye1138]

Hey guys,

So yea, I have a beautiful set of Faber 45's, BlueSteel valves + manifold and some bands. I bought the kit more then a year ago from someone I found on ebay. I went through some financial strife and now that I'm back on my feet and wish to go diving, I'm looking at the rig and noticing the two tanks are bowing slightly from bottom to top.

I pulled the bands off and everything is perfect, the top band goes on, no problem. But once you put the bottom band on, it takes a bit of wiggling to get it on and the moment you tighten it down, the bottom of the tanks bend inward slightly, maybe 1 or 2mm, not enough to really see unless your in front of them staring at'em.

So... I bring it over to my local shop for Hydro, we're re-assembling today and wow, the issue is quite noticeable with the rig apart. They wouldn't even let me re-assemble it at the shop citing liability reasons.

So here I am with a big conundrum... do I just forget about it and go diving, or do I spend a considerable amount of money buying different bands in order to perhaps remedy the issue. ?

With the bands locked down, I can twist the manifold barely, but its a hard twist...

Here is the rig, but you really can't see the issue as the camera lens has more distortion then the tanks do! heh

 

[lowviz]

BTDT. http://www.scubaboard.com/forums/vi...free-pair-double-50s-today-2.html#post5543905 (sorry, I pulled the pics long ago)

The two bands are probably not from the same set. The tank separation is important, the manifold will give you a wide latidude of center-to-center adjustment, but the two bands have to be the same.

Me, I'd just cut and add a strip of the proper thickness SS sheet under the "pulling" band to make the tanks appear larger in diameter for that band. (Duct tape?)

 

[tye1138]

Me, I'd just cut and add a strip of the proper thickness SS sheet under the "pulling" band to make the tanks appear larger in diameter for that band. (Duct tape?)

WOOOOHHH I like that idea. Thats usin' your noggin! Thanks!

However... I do think its the opposite issue. The upper band fits perfectly, the bottom band fits too tight. So wouldn't adding size make it even tighter? Darn things look identical when you hold them next to each other or on top of one another. The difference is so minimal, its hard to see.

 

[lowviz]

Tighten them down until they just grab and measure the distance between the "stiffeners". If wide, they lock up quickly, if narrow, they seem to just keep going. Let me know, been a while, I could be wrong...

I solved the problem by tightening everything down just snug, fussing with the fit, and finally tig welding the two "half-bands" to the stiffener plate, fully assembled in place with a tank at either side. OK there was only 800 psi or so in either tank but that was rather disconcerting.

 

[tye1138]

Hmm, you did give me an idea... dang I just built the darn rig too!

 

[lowviz]

no worries, it never ends...

 

[Scared Silly]

Before going through anything with tape I would swap the band arounds (put the top one on the bottom and visa-versa) then flip them upside down. Then swap them front to back. That will give 8 different ways to assemble the bands. If none seem to solve it then swap the valves on the cylinders and try again. That is now 16 combinations. There is enough tolerance difference that I would find the best (where the crossover turns the easiest) and call it good.

 

[Akimbo]

This worked for me. You can set the minimum distance between cylinders by cutting two pieces of metal or plastic to width and centering it on the draw-bolt with double nuts. Here is an image of double 45s. The bolts are temporary non-stainless used for fit-up.

Like others, I wasn’t satisfied with the width of my purchased bands; all O-rings were not engaging and I wanted the rig to be narrower. This particular set of bands were made in two C-shaped pieces with ears so I ground the welds off, set the width I wanted, and re-welded the edges. The holes were misaligned at that point so I had to chase the holes with a drill.

I ran a piece of ½" cutting board (high density Polyethylene) through a table saw to width, drilled holes, and cross-cut for the two separators. That ensures equal widths which forces cylinders to be parallel.

Having these separators in position is a great indicator showing much the cylinder move as the bands are tightened — it’s a lot. Keep the isolation valve loose but close to the desired position as you tighten the bands. Verify that the valve rotates on its threads (one left and one right-handed like turnbuckles) every few turns on the band’s draw-bolts. This will indicate that the manifold is not binding or being stressed during assembly.

Rotate the isolation valve to the position you want after the bands are tight and pressing against the separators before locking the two manifold jam-nuts. You should have about 20-40° of rotation with the bands tight before the threads bind. You can modify the width of the separators if you don’t like the isolation valve position. It is labor intensive but gets you what you want and makes a very secure assembly.

 

[tye1138]

Before going through anything with tape I would swap the band arounds (put the top one on the bottom and visa-versa) then flip them upside down. Then swap them front to back.

Yep, that was the first thing we tried. The upper band is perfect, either direction and the lower band seems to be too tight when tightened down. However, perhaps I'm tightening them too much, that could also be part of the problem.

---------- Post added September 25th, 2013 at 04:12 PM ----------

Akimbo, great advice, I love your mockup, looks great. Wish I had the tools to make it happen, but sadly it would take me quite a long time to mock something up like that. However I can probably come up with an alternative... Let me go play this afternoon and see what I come up with based on your tips!

Ohh on a side note the shop I had send them out for Hydro, laughed their asses off about my little rig. One guy said " they don't make anything like that anymore, looks like its from the 50's or something". He was being serious and was shocked when he saw the manufacturer date was 2008. Ya know, I've been in the industry for 14 years and I could tell you from 200 feet away what tanks I have and when they were made because every tank is different and Fabers of that vintage all look the same. So this guy who runs a dive shop for a living, sells doubles, uses doubles, is a huge double guy... and he was shocked by the faber 45's? Its a strange world out there!

 

[Akimbo]

Let us know what you learn. I am not sure exactly where the problem with your bands are. Too narrow, wide, out of parallel, or some combination? There are a lot of people who don't know how to properly assemble doubles... especially at dive shops.

Dive Rite has a pretty good video on YouTube:

https://www.youtube.com/watch?v=rsFpMuANKag