Double tanks not the same size

[kelvinbatista]

Hey guys, I recently found another hp100 to double up with one I already own. They are both Worthington x7's and are only off by a 2-3 years. However after putting them together we realized they are not exactly the same height. One has a slightly longer neck and stands just a bit taller than the other. Is this something I should be concerned about? (in terms of buoyancy characteristics.) Thanks in advance

 

[BB`]

In theory they should be nearly the same but the only way that I know of to test is to actually jump into a pool and see.


With that said, I would keep looking and find identical tanks to prevent the rig from being crooked/uneven when sitting on a bench.

 

[2TH DIVR]

You could try putting a shim in the boot of the short tank.

 

[bamafan]

You will probably never notice it in bm doubles. Now sm would probably be different.

 

[runsongas]

if you are close to the bay area, let me know. i got a buddy with the same problem with his x7-100s, you could contact to see if you guys could swap and get your tanks matched

 

[tomfcrist]

They will band together just fine, and as long as they are the same overall height, they shouldn't be too far off as far as weight and balance is concerned.

I dive mismatched 72's quite a bit...never know it in the water.

 

[Brandon]

I have the same issue with one of my sets of Worthington HP100s. The neck is about 1/2" longer than its partner tank. They sit a little lopsided when resting on the floor. If another set of doubles is nearby, I can tell that the crossbar is slanted slightly. Otherwise, I don't notice and it makes no difference underwater or while gearing up.

A 1/2" tall ring of steel from the tank neck might weigh all of an ounce. I wouldn't worry about it.

-B

 

[Steve_C]

By accident when i bought my HP100s they were the shorter ones. Being short myself I really appreciate a shorter tank.

 

[kelvinbatista]

Thanks for the quick replies. I'm actually in NY. I wasn't so sure how big of a deal this was.

 

[DA Aquamaster]

Some one mentioned a canted crossbar above.

If the cross bar is not straight then it's stressed to the point of being bent, which is really bad.

When assembling doubles you set the tanks on their backs and get the cross bar started evenly in each valve 4-5 threads and then slide the bands on under the tanks and get them properly positioned and spaced.. Then as you start to tighten the bands, you adjust the cross bar length as needed by turning it one way or the other to keep the tanks parallel. The cross bar should continue to be easy to rotate, even when the bands are fully tightened.

At this point the cross bar will also be straight, and the tops of the tanks will be level. If the bottoms don't match, it won't matter much if the bands are suitably strong - unless of course you drop the tanks. That's bad any way, but worse then the bottoms are not even as if they land square, the shorter tank will want to slip in the band and the direct in-line impact may be enough to do that and bend the manifold in the process. If the bands are slightly loose, that's guaranteed.

Other wise, if the tanks impact at an angle then the vector applied to the tanks in the band is reduced, and it take a larger wack to bend the manifold. But, if the difference in height is significant, it's not a bad idea to shim the short boot so they stand level, if you plant to use boots and stand your doubles upright.

I bought a set of doubles from a complete and total moron who shipped them with the manifold assembled and the bands loose in the belief they'd be less prone to damage that way. I can't imagine what he was thinking shipping them assembled instead of as two tanks and a manifold in 3 separate boxes. The manifold had about a 1/2" bend in it when it arrived and one of the valves was bent as well. The jerk never did pay for the damage.

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Steel 72s were made for decades by several manufacturers and getting a pair that match in terms of height, shoulder and neck profile and buoyancy profile can be a challenge, unless they are very similar age and from the same manufacturer and even that's not a guarantee.