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Submersible Waterproof Seals

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Hon1nbo

Thu Apr 22 2010, 11:10PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040

Hello everyone,
as you may know that in the Project board I am working on a Remote Operated Mini-Sub. However, even though my first set of seals worked wonders, my new ones are causing issues and I have resealed them several times. I feel that part of the issue is that I can't do anything from the inside of the case due to the fact that ammo cases are end serviced only.
I have started reconsidering using one of my Pelican Cases. I dunked my 1550 case, and it let a lot of water in (the seal may not be seating right with 65 pounds of Ballast weight in it).
I then dunked my 1600 case and it appears after 25 minutes to be holding just fine, and I am letting it run longer to be safe.

I feel that using a plastic Pelican Case would make things easier to seal for a couple of reasons: plastic is easier to make controlled cuts that are too large for drill bits I can buy, unlike the steel ammo case which has fairly poor cuts. Also it has a lid which makes everything easier to maintain. I may have to rebuild the PVC frame due to the Pelican's size, but that is easily done in a couple of hours, and I may not even have to. I will keep the original electronics board etc.

Anyways, I am still debating which type of sealant to use for this, as each one has had a problem to some degree. The Silicone has let some water in but not much, I originally thought that that little bit of water came from not sealing the cable going to the waterproof connector right, but I noticed that the water was on the outside of the compression fitting, meaning it came between the connector and the steel hull where the silicone seals things. Also, Silicone is expensive in this amount in which I need a very good and seal

Gorilla glue expands and fills large gaps/cracks/seams easily, but I think it may be too hard and therefore when under stress it will fail.

Since I can maintain things from the inside now and that my holes and gaskets won't be irregular, I might be able to get away with a gasket on both the inside and the outside of the connectors and a little bit of sealant.

Are there any suggestions you guys can come up with?

-Jimmy

EDIT: it turns out the smaller 1550 fits inside the 1600, I may use it as an Inner Compartment for the electronics that do not have one already... I may just drill bolts through it and seal them with Epoxy and Heat Shrink to prevent shorting in presence of water, but leave some unprotected as my water indicator... even though the 1550 didn't fare well on its own, it should be a lot better without the large amount of weight and being an inner compartment.

with this design, I might be able to push the depth limit of my design.

Carbon_Rod

Fri Apr 23 2010, 09:30AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

Depends how deep you want it to go:
* Electrical Encapsulating Epoxy Compound + plastic container
* Fill leaking cavity with Mineral Oil or Paraffin wax
* Alka-Seltzer tablet + rice to pressurize failing compartments and remove condensation

Cheers,

Proud Mary

Fri Apr 23 2010, 09:31AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Could it be possible to fill your device, or parts of it, with an incompressible non-conductive fluid? If it's incompressible, nothing can leak into by dint of external pressure.

Hon1nbo

Fri Apr 23 2010, 12:14PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040

Proud Mary wrote ...

Could it be possible to fill your device, or parts of it, with an incompressible non-conductive fluid? If it's incompressible, nothing can leak into by dint of external pressure.

I have to be able to service my containers easily and in the field, so that is likely out of the question especially since the demonstration is in a pool.

I may be able to go with epoxy and a plastic container, but I wonder if I really needs the container because unlike other ROVs I have Panel Mounted Connectors designed for water, I really just need to seal in between the connector and the hull, and it should be easier now that I have a lid opened container because I can now make sturdier connections etc because I can reach them.

I thought about a double gasket system with either some epoxy or silicone, would that work?

The current depth goal is only 30 feet or so, but the deeper the better as I will simply upgrade it in the future if need be.

Also, if it matters since pressure keeps being mentioned, these Pelican Cases all have an Automatic Pressure Relief Valve on the front of them

-Jimmy

IntraWinding

Fri Apr 23 2010, 12:59PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

Hope this isn't too obvious: Silicon's good stuff but watch out for the acetic acid fumes from the usual type. You can find 'non-acetyl' formulations too. The stuff for constructing fish tanks from plate glass is probably a good bet. Try to make the seal so it gets tighter as the pressure increases. For example, if you have a wire going through a plate, make the hole tapered so it's larger on the outside. Seal the wire in with silicone and allow to set. When you apply pressure the 'bung' fits tighter in the hole and squashes the wire tighter.

Alan

Proud Mary

Fri Apr 23 2010, 01:10PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

You might also think of putting some positive pressure in it - pump it up through a bicycle tyre valve bonded into the case to a pressure of 200kPa which will keep water out to a depth of 10m.

Hon1nbo

Fri Apr 23 2010, 01:48PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040

Proud Mary wrote ...

You might also think of putting some positive pressure in it - pump it up through a bicycle tyre valve bonded into the case to a pressure of 200kPa which will keep water out to a depth of 10m.

I might be able to try something like that, but these cases have an Automatic Pressure Purge Valve, it won't let water in but it will let Air out. I can't quite keep a pressure difference, as it is like scuba, all pressure matches that which is around the diver.

At other message, I used aquarium sealant for the first connectors and got good results, a little Ayer but that water may have spilled over from elsewhere, I'll stick to that for now but Ill also make a gasket for the inside of the case as well as the outside so I can add Layers of protection.
However, the compression method you described would not work due to qdformentioned pressure issues

I have already mounted, but not yet sealed, the electrical connectors.

I'll let everyone know how it goes.

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