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Heat shrink tubing (HST) as a pressure barrier


(Richard) #1

@Rusty-Has your team gathered any information on this? Of interest if you have to make a splice outside of the WTE. I note that some HST has an internal adhesive activated by heat.

Richard


(Rusty) #2

Richard,

Yes. We’ve used it often and it works really well! We also occasionally use regular heat-shrink tubing but cover the splice in a rubberized coating first and then shrink until the coating squeezes out the sides to ensure it is filled.

If you try it, let us know how it goes. I’d be happy to carry the tubing in our store if it is helpful to people.

-Rusty


(Richard) #3

Okay, thanks.


(Harold Scadden) #4

Just a word of caution … flood out time.

The epoxy in the HST heat shrink is great for sticking / sealing stuff around wires/cable but it is not made for pressure. I have only seen one company that makes a splice kit using a similar concept that you have stated and that is Reltek. I have used their products and I have also paid them to do laboratory testing for our company … they have their ducks in a row.

Go check for Splice Kit on the lower left of their webpage for “Product List” at http://reltekllc.com Could get the link to post correctly. One big thing, it will cost you money but their stuff works to the bottom of the ocean and back.

 


(Harold Scadden) #5

Rusty,

Heck on another note, you might want to look at some of Reltek’s potting compounds. Like I said this stuff is expensive but man it works REAL well and they have a ton of years experience with this stuff. In fact the owner helped setup our shop 22+ years ago. He was one of the many technical consultants that we brought in and the Government has contract this guy out for many projects over the years.

 


(Richard) #6

Harold,

Keep in mind my work is mainly in shallow depths (50 -130 feet) because that is where the reefs are and I am on a very low budget. To me, innovation and experimentation is part of the pleasure of building something. I am always looking for ways that will get the job done but not be so expensive. These days you can just buy what you need off the shelf, but typically it is over engineered and consequently overpriced for the depths of my intended work. I know this sometimes leads to failure, but I view it as just part of the process of exploration. I want to keep the pressure on Blue Robotics to develop components that the hobbyist can afford. We can help them do that by trying new things and giving them information on what works and what doesn’t.

Regards,

Richard


(Harold Scadden) #7

Richard,

Understand your take because of budget. I was commenting on experience. I am looking at a range of 100 psi (just a hair over 200 feet) is to ensure that the cable is jacket is prepared properly in order to increase your success. It all boils down to lap shear forces where the heat shrink and the cable are “bonded” with the adhesive. For this depth range, I would highly recommend that you take the cable jacket and lightly sand it so the jacket has a rough appearance. You don’t want to get to crazy because you will cut through the jacket in no time at all.

Once you have lightly sanded the area, then I would clean that area with a two pass system. I would first use MEK with a cloth, not paper towel, to clean the residue that the sanding left behind and to degrease the surface of the cable. Somewhere on here is a guide that I wrote up on how to pot the penetrators. You will see a picture in there with black residue on it that the MEK stripped from the jacket after sanding … you want this.

The sanding helps to greatly increase the surface area of the jacket by increasing the pores on the surface. After treatment / cleaning with the MEK, then I would do a single pass wipe with Acetone. This is a zero residue solvent and you will now have a surface that is as clean as you are going to get it.

Since the cable jacket is pretty thin, I would create a boundary where you only sand and area say .5 to 1" on either side of the splice. I would clean an area twice that boundary with the two solvents. Then the next step would be to use the HSS heat shrink that has a “shrunk” diameter that is smaller than your cable diameter. You do not want something that is close … you want a nice tight seal.

That is pretty much if for what I would do. Now if you want to test this procedure out and not loose hardware … take a piece of cable of the same type that you plan on splicing etc. and make it long enough that you can put a weight on the end of an area and stick the item over the side and run it down as far as you want not to exceed say 200 feet. LEAVE it there for a while and what you can do on the surface is measure continuity between the conductors. I would recommend making sort of a splice end cable area that you have sections of the conductor insulation removed to act as a wet probe inside of the “test” splice region. If your wire is say 200 feet long and you know the resistance is XX amount … you shouldn’t read anything between the two wires but a dead open. Once you get water intrusion you are going to start to read a high resistance short etc…

If you have a megger, then you can test for a better quality factor of how well the splice is holding out.

Harold

 


(Richard) #8

Thanks, Harold, I appreciate your instructions on using HST and will follow it to the letter. I am going to use 3:1 shrink ratio, half inch diameter HST, to splice a 1/4" cat5e cable, so this should meet your recommended requirements.

Richard


(Charles Rounds) #9

There is a sealant used for fuel tanks by the military. Several manufactures produce similar sealants. PRC Desoto - PS-890 B1/2 Gray Fuel Tank Sealant works wonders. It is a bit pricey, and rather obnoxious to the nose, but well worth it. Once applied you will not have to revisit.
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