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Aluminum vs Acrylic Tube 4''

Hello everybody,

I checked the inner dimension of Aluminum & Acrylic Tubes 4’’ and I notice that there is some minor difference:

Aluminum Tube 4’ inner dimension: 100.65
Acrylic Tube 4’’ inner dimension: 101.19 (+/- 30)

Is this difference affect the max depth rate of the two tubes?

My concern is that I am having a big difficulty to put the flanges to my aluminum tube and I have decided to open up the inner dimension using a professional lathe. At the same time it is very easy to put the flanges to a acrylic tube.


I find that it’s easier to put the flange in the acrylic tubes than it is to put the flange in the aluminum tube. I just add grease to the o-rings to make it easier.

How old are your ALU tubes?
I have seen older tubes that seems to be a little bit more tight.

I have used many of them for the last few years and I can’t say I’ve noticed a trend in them being looser or tighter.

Hello All,
I converted from 4" acrylic to aluminum with considerable pain. I could not press the flanges on the aluminum tube the same way as the acrylic; by placing the dome end against my chest pushing from the rear flange.
The solution was to:
use new lubricated o-rings
cut a 3 5/8" hole in my work bench
stand the tube on end over the hole so the camera would clear
stand on the bench and pressed down with all my might until the rear flange seated
started the dome flange in the tube
placed the dome end over the hole
pressed down with all my might until the dome flange seated
good news it held a vacuum for over 24 hours…

There is no way I could open the tube at sea and re-seat without the above.

Hi @Larz:

The flanges do fit very tightly in the 4" aluminum tube. But you shouldn’t have to go to that much trouble to get them installed. It helps if you use the hand vacuum pump to create a vacuum in the tube. It’s kind of a three-handed operation at first, you have to have the flanges pressed against the tube with enough force that they’ll seal- then attach the pump to the enclosure vent port, and pump the internal pressure down as far as you can. With this internal vacuum, the flanges will snap into place with a modest push. Just keep your fingers out of the way of the flange! When it snaps into place it will pinch anything in its way.

Things are more interesting when removing the flanges from the tube. There are notches in the flange that can be used to pry the tube off, but the aluminum is very soft. I use thin, flat blade screwdrivers, with the flat blade covered with some adhesive-lined heatshrink. The heatshrink serves as padding for the aluminum, the adhesive lining keeps it from twisting off of the screwdriver. This works well for screwdrivers whose blades are 0.8-1.0mm thick.

Good tip with vaccum!
For dismantling I have another tip:
Unscrew 2 screws 180 degrees from each other holding the endplate to the O ring flange.
Screw in 2 longer 3 mm screws, they now act as puller to “push” out the hole flange.

I have compared 4" alutube R1 with a new latest version R3
Inner sealing diameter is the same.
But a difference is that R3 has an extra small 45 degree edge on the inside.
That means it helps the O rings to not get cut, like the sharp 90 deg corner of R1 does.