Setting up doubles

[Mike D]

I was setting up double 100's and everything was going smoothly.....I noticed however that when I put the bands on the tanks the crossbar did not move smoothly at all. Is this a problem? Stress on the crossbar or is it supposed to be like this?

Thanks for any feedback.

 

[Doc Harry]

If I understand you correctly, you mean that once you tightened the bands, the crossbar (with the isolator valve) did not rotate easily or not at all.

Either the bands are too tight, or the spacing of the cylinders as determined by the crossbar is significantly different than the spacing as determined by the bands. In that case, when you tightened the bands you applied torque to the crossbar, distorting it somewhat. This is not good, and prevents you from rotating the crossbar.

What I would do is loosen the bands and spin the crossbar so that there is very little torque on the crossbar. Which direction do you spin? It's trial and error. Spinning one way will move the tops of the cylinders apart, spinning the other way will move them closer together. Experiment until you're sure that the spacing of the cylinders is the same with the crossbar as it is with the bands. The cylinders need to be parallel so that when you tighten the bands you are not applying torque to the crossbar.

Then slowly tighten the bands and periodically check to make sure the crossbar still spins slightly. You may have to spin the crossbar one or two times in either direction to find the point of least torque. If you really get the band bolts super tight the crossbar won't move at all even if the spacing is correct. I don't crank the bolts on my band super tight. I just make sure the bands are adequately snug and my isolator valve can rotate slightly (about 30 to 45 degrees) in case I accidentally bump it.

When assembled correctly, the isolator valve should stick straight up or slightly forward, and easily rotate backwards 30-45 degrees if bumped.

The other reason your crossbar might not rotate is that you have the crossbar lock nuts tightened down. Some people like to tighten these nuts so that the crossbar doesn't rotate, that way the isolator valve stay put. But I don't like tight nuts, I like to have my nuts loose (something Freudian there) so that the isolator valve "gives" when bumped.

 

[JBRES1]

Check this out.

http://www.trishandjason.com/scuba/HowToAssembleDoubles.pdf

YouTube - Dive Rite How to Assemble Double Tanks

Hope these help.

Jim breslin

 

[Doc Harry]

http://www.trishandjason.com/scuba/HowToAssembleDoubles.pdf

I really, really dislike this method.

I can't watch You Tube at work.

 

[The Kraken]

When assembling doubles, I apply the bands first, snug them up, and measure the center to center distance between the tank valves, record the observed dimension, remove the bands, adjust the manifold close to the observed dimension, attach the manifold, bands and then adjust and tighten.

the K

 

[DA Aquamaster]

Doc Harry's advice is well stated. I'll just add/clarify that as you tighten the upper and lower bands they will move the tanks outward slightly so you need to be sure you adjust them slowly, progressively and evenly so that the tanks stay parallell to one another to keep the isolator from being stressed.

I am from the tighten the bands "supertight" school of thought as I have seen way too many isolator bars bent when the "less than supertight" bands let a tank slip. Tighten the hell out of them, just be sure to tighten them evenly.

Same with the isolator bar itself. I prefer mine to be tight. The knob itself is rubber (if not, swap it for one that is) and breakage is very unlikely. If you impact an overhead hard enough to break it, you have bigger issues. On the other hand, if you leave it loose, it is possible for it to get rotated aft in a relatively soft contact with the overhead, moving through a restriction, etc where it can then be difficult to reach if you need to isolate. Generally speaking it does not make much sense to trade the risk of a low probability event for the risk of a much higher probability event.

Consequently, I like my nuts tight because it ensures my knob will always be where I left it.

 

[cool_hardware52]

When assembling doubles, I apply the bands first, snug them up, and measure the center to center distance between the tank valves, record the observed dimension, remove the bands, adjust the manifold close to the observed dimension, attach the manifold, bands and then adjust and tighten.

the K

This is my preferred method also.

Tobin

 

[UCFKnightDiver]

Also, leaving the crossbar loose may cause premature wear on the barrel o-rings, and these are not something you want to have fail!

 

[Texasdivechick]

Consequently, I like my nuts tight because it ensures my knob will always be where I left it.

I'm sorry. This is just funny.

 

[The Kraken]

DA has a point.

I guess I'm just an over tooled tool nerd, but I actually us a torque wrench to tighten the tank bands and the lock rings on the manifold.

the K