[PSUBS-MAILIST] cable fittings

[Ian Juby via Personal_Submersibles]

Hi Rick,
I saw your post and wanted to ask if you meant electrical or plumbing
through hull connections. So I'm glad you reposted because I haven't been
able to follow the thread, nor have I had the time to go back and look
stuff up.
When I was working R&D on our diver heater system, we used a watertight
bulkhead connector for the shot line and remote control. Unfortunately,
this was over 20 years ago and I was not the one who actually ordered the
connector. So I innernets'd some pictures to try and hopefully find it
again because I remember quite well what it looked like, its design and
construction. The closest thing I could find was Teledyne Marine's "Wet
mate" connectors:
http://www.teledynemarine.com/electrical-wet-mate-connectors/
I couldn't tell you the price, but I'm sure they weren't cheap. For my ROV
project, I'm still in the rough design phase and I keep increasing its
depth capabilities. So I'm just going to make my own through-hull
connectors, and they will be similar to this design.
The through-hull seal is accomplished by a simple and reliable o-ring
(which doesn't appear in teledyne's picture). Basically, the rubber
connector body is mounted to a brass threaded tube that goes through the
bulkhead. The brass threaded tube has a seat for an o-ring which gets
compressed by both the nut and external water pressure. Here, I drew a
pretty picture:

[image: bulkhead connector.jpg]
I just realized I didn't mark the brass tube, but it's the part that goes
through the bulkhead.
The particular connector we were using only needed to go to like, 300 feet.
I believe we tested the heater unit to 300 psi and ironically, it was the
swagelock fittings inside the unit that leaked - that electrical connector
never leaked. We had I think 8 electrical connections passing through that?
We could get the identical connector as a straight-through connector, and
not an angled connector like my drawing.
The pins and sockets were the solid style - in other words there was no
splits to allow for expansion or contraction of the sockets or pins. This
further added to the waterproof nature as now the wire (a possible leak
point) was buried in solid rubber, behind a solid metal socket which itself
was buried in solid rubber. Any water wicking along would have to travel
1/2" along the metal/rubber just to get past the socket.
The connector body was a hard rubber, both the through-bulkhead block and
the male connector. Under high pressures, the water can wick along the
inside of the wires (between the copper and the outer insulation) or if you
pass the wire through say, silicone rubber, it can wick along the junction
of the outside of the wire and the encasing rubber. So the longer that
travel distance is, the higher the pressure needs to be to force water
through those avenues. That rubber block was only maybe 2 inches left to
right in my drawing. I don't remember what pressures or depths it was rated
for, but I guarantee you it could take a LOT of pressure. Mechanically
(because the bulkhead hole was small) and in keeping watertight. The
biggest risk for a leak was if the bulkhead got a scratch where the o-ring
seated against it. I have no doubt that connector could have taken
hydraulic pressures (thousands of PSI).
I did not draw this in my pretty picture, but the head of the brass tube
probably had multiple rings inside the rubber, both to get good mechanical
locking between the rubber body and the brass body, and to make the
greatest distance the water would have to travel to get around from outside
to inside the tube, if it were to wick along the junction between brass and
rubber. But I'm speculating there because I didn't cut one of those
connector$ open to find out. Lest I get fired and stuff for destroying a
connector worth hundreds of dollars, you know.  :D Just, when I go to make
my own connectors, I'll be making the mounting tube like that, for those
reasons. The rubber that made up the connector body filled everything,
including right to the bottom of the brass tube.
The nice thing about making your own connector as well is that you can make
the electrical pins, sockets and wires any size you want to match your
electrical current needs.

These particular connectors could be plugged and unplugged underwater, but
I suspect it would be very difficult to do as it would have to displace
water or vacuum from the connector holes. But as you can see, the male pins
had insulating rubber for a part of their length to maximize the distance
the electricity would have to travel from pin to pin, thus maximizing the
electrical resistance from pin to pin as well.
Hope that helps,
Ian


On Mon, Jun 8, 2020 at 12:09 PM Rick Patton via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> I posted the other day about cable threw hull water tight fittings and
> only got one response back and was hoping for more feed back as I know most
> of you probably don't make your own so for the ones that buy them, is Blue
> Globe the only player out there besides sealcon?
> Thanks
> Rick
> _______________________________________________
> Personal_Submersibles mailing list
> Personal_Submersibles at psubs.org
> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.whoweb.com/pipermail/personal_submersibles/attachments/20200608/af7b1833/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: bulkhead connector.jpg
Type: image/jpeg
Size: 1815641 bytes
Desc: not available
URL: <http://www.whoweb.com/pipermail/personal_submersibles/attachments/20200608/af7b1833/attachment-0001.jpg>