n00b doubles assembly question

[marchand]

Yep, make sure you get that nut pretty tight.

 

[HullBlister]

It also just dawned on me that I was "testing" the install with an non threaded BP. So there was no spacing given by the webbing that basses behind the BP.

Really.

Sometimes I just wonder how I manage to walk upright most days.

Blister

 

[micklock]

This might help if your still having trouble
Assembling Double Cylinders

 

[astrofunk]

It also just dawned on me that I was "testing" the install with an non threaded BP. So there was no spacing given by the webbing that basses behind the BP.

Hm, that doesn't make sense to me. Unless you're doing something unusual with the webbing, it won't offer any additional spacing between the plate and the tanks.

For what it's worth, here's a pretty good resource for webbing your harness:

Webbing a Harness

There are a couple of different flavors of bolt kits out there, each with a slightly different style of assembly. Can you upload a picture of what you've assembled so far? I'd be happy to talk you through it (others too, I'm sure), and perhaps we can help trouble shoot for you.

 

[Gombessa]

Hm, that doesn't make sense to me. Unless you're doing something unusual with the webbing, it won't offer any additional spacing between the plate and the tanks.

Right. In reality, the thing that determines how many threads protrude through the front of the backplate is the depth of the channel in the plate. While it seems like having the webbing grommet would decrease that, in reality it doesn't affect the spacing.

Also, if your bolts are truly sticking out far enough to hit you in the back (they would need to be out so far that they would hit the ground if you laid down the tanks face-down, there's no way you would have insufficient threads for the wingnut with the bp/w installed.

 

[HullBlister]

Well I fixed the problem.

I ran to the local West Marine and got some thicker SS washers for the bolt heads, and some SS wing nuts that had shorter "wings."

Now all it right in the world.

Thanks for everyone's help.

Now I have to find a use for them before there is too much ice on the lakes.

Thanks again,
Blister

 

[Graeme Tolton]

Correct me if i'm wrong here, but if you aren't able to assemble your gear correctly, how are you able to use it correctly? Any technical course SHOULD be covering gear selection/assembly. If it were myself, having questions like this would make me question my training and whether I should be doing what I am attempting to do.

 

[JahJahwarrior]

Tip that has helped me reassemble doubles a good bit faster: Turn the isolator section backwards in the valves, you should hear it click. When both sides are clicking, it should be lined up, and then turn it the correct way and it should catch on both sides at the same time.


OP--go read some guides to this stuff, and find someone with doubles who can help you to make sure you are doing this right! Doubles aren't as hard as many people make them out to be, but if you don't know what you are doing, you can have bad results. Fortunately, most fill stations wouldn't have filled doubles which lacked bands

 

[DA Aquamaster]

The bands impact the alignment of the tanks as you tighten them. Ideally, the tanks are parallel to each other with the centers aligned so that the manifold is not stressed. as you tighten the bands, you spin the isolator valve/crossbar one way or the other to ensure it continues to freefly spin - indicating the crossbar is properly separating the valves and is not stressed in tension or compresson.

So in effect, adjust the cossbar lenght initially to be in the ball park, then turn it one way or the other ensure it remains in a range where it will freely turn one direction or the other as you tighten the bands equally - and in the process keeping the tanks parrallel.

The actual function of the bands is two fold: 1. provide an attachment point/interface between tanks and backplate and 2. carry the load of the tanks and ensure they remain properly aligned and parallel to each other, preventing any significant loads from being carried by the manifold.

If care is not taken in establishing and maintaining the correct lenght on the crossbar, the bending loads that will be imposed on it can be immense as the bands are tightened on tanks that are not parallel due to improper crossbar lenght. That improper loading can lead to failure of the manifold.

A few generic tips:

Correct bolt lenght is usually a function of the depth of the channel in the backplate. Some plates are flatter than others and end up needing longer bolts.

With fully threaded bolts it is often easier to clamp the first section of band betwene the head of the bolt and a jam nut. That allows you to tighten the second nut on the outside of the bands from one side only.

Set the centers at 11" exactly. A plate with two round holes spaced 11" apart works well as a guide. Many plates have a slot in the lower half of the plate that allows the bolt centers to be off a half inch or so, but that can be problematic if you switch plates or loan your tanks to someone else. Loosening and moving the bands later (and usually on full tanks) can result in the manifold being stressed if the alignment of the tanks changes.

Getting both ends of the crossbar to start on the same turn can be a challenge. If the turning it backwards tip does not work, start one side 1/2 to 1 turn only. Then you only have to focus on starting one side instead of both. In most cases the 1/2 to 1 turn difference in threads on the left and right sides won't make any difference unless the band centers are unusually narrow.

 

[BabyDuck]

and be sure to use vise grips & adjustable wrenches - right?

(private joke with previous poster - )