Tips for the Electronics Tube Closing Caps



We wanted to ask if you guys has any tips on the caps that close the water proof tube housing the electronics. How do you cap it on sides so that it doesn't leak water in 20 meter depths in? The caps don't seem to be a part of the AutoCAD drawing (at least not in the version 2.2). Is it okay to just cut two round acrylic pieces of just the right size that we will have to force push in on the sides to isolate the internals of the tube from the water outside? This sounds a bit cheesy to us. Is there a better way? Also, how do you get the wires out of that tube without water leaking in?

Thank you,




This is an old thread and I am not sure what geometry you were originally referring to. But for others sake I would recommend using O-ring seals. They are easy to design, manufacture and the interfaces are removable and pressure rated up to to 1500 Psi and beyond. To design proper O-ring interfaces I would recommend using Parker-Hannifin design guide click here. There are a couple of ways to accomplish an O-ring seal interface: Face seals or Radial Seals. I prefer radial seals because the compression is set when you manufacture your tube and end-cap (Reference Page 4-5 in the Parker-Hannifin O-ring design guide) or image below:

Thank you,




Here is an interface I commonly use with proven real world results. I typically use QTY (3) fasteners, for small diameter applications) but one could use more. The fasteners are not really designed for taking the external hydro-static pressure load as the shoulder of the end-cap is pressing circumferentially on the outer-housing. Although technically at greater depths the fasteners could start to experience shear and bending loads from end-cap deformation (material dependent) but for the most part this will not be an issue.

The design intent of the fasteners are to create a removable "pin" that locates the end-cap and allows for easy assembly and dis-assembly. Notice the dual O-rings. You only need QTY(1) O-ring to seal but I use QTY(2) for redundancy. It is cheap insurance should you unknowingly damaged or contaminated your o-ring during end-cap installation.

Design Considerations:

1) Use larger O-ring diameters than pin hole diameters. If you do not, the O-ring will try to extrude out of the pin holes in the outer-housing and will cut your O-rings. With fatter O-rings this almost never happens .

2) Always use O-ring lube for O-ring installation. I prefer Dow-Corning DC-111 click

3) Should you have to have small O-rings relative to the diameter of your pin holes, located in your outer housing as seen below, you will need to create an installation tool to plug the holes in the outer housing-as I had to for this assembly. The installation tool was designed and 3D printed on my U-print.

See images below: