DIY rebreather under construction

Ekke

Do you know is there any problems with PVC-U (Unplasticised Polyvinyl Chloride, we use Georg Fischer)? It's hard, and pretty good to machine, but "chips" are pretty endless . We don't think that PVC(-U) is a brittle material, it has been used in DIY diving lamps (hand held, not ours) with no problems even at cold temperatures (-20'C and so.. although at least one exploded but it was "a design error".. hydrogen + spark = nice combination ).

And we use thick walls, maybe we should still do some sledgehammer test when it's cold outside.. only ~0'C today, almost like in summer..

Anyway.. thermal conductivity of PVC is so poor that our scrubber should have better insulation property than K1 with more than 1/2 thick walls (if I remember right and it has PE pipe..). Hope it isn't too insulating.

-Mikko

Duncan Price

UPVC is used in a lot of our kit for certain applications. We use both PVC (grey) and PP (off white) George Fischer components and I've been looking longingly at them as the basis for my next rebreather. PVC tends to be solvent welded but PP is heat welded.

Creep can be a problem with all plastics - I've just been measuring the spring constant of some polymer springs and they creep a lot.

Low thermal conductivity can be good or bad. We have some plastic heat exchangers which are huge and very expensive.

Ekke

Ok, thanks! We use (Henkel) Tangit to "glue" parts together, glued joints should be as strong as base material.

I don't think that creep is a problem, because there isn't any big forces to PVC.

Is there PVC scrubber in one of the KISSes? Do anyone know how thick it is? At least it's easier to make walls thinner than vice versa.

-Mikko

Ekke

Yeah.. Little progress.. We made a neoprene counterlung today with Pasi. It doesn't have any holes yet, and it keeps air inside without glue, but we will still glue it.. Now it's only sewed, was little harder than I first expected..

I hope we get both ready before weekend..

-Mikko

Ekke

Slight progress, but things are going pretty easily. Thanks for the CAD planning. I made skeleton frame today, still unaccomplished. I don't have full access to workshop in next two weeks, so things are not going as fast as I would like.

http://ekke.kapsi.fi/sukellus/INDEX/kuorrutusta.jpg

-Mikko

Bnscherm

What thickness neoprene are you guys using for the counterlungs?Any tips/techniques for sewing and sealing neoprene CLs that you've found?

Ekke

We used 2mm. It's not very hard if shape is simple, but our profile was little complicated to do with only one seam.

-Mikko

Bnscherm

The 2mm neoprene foam (wetsuit material) or sheet neoprene rubber? Is it nylon coated on one or two sides? I've been doing some testing with vinyl CLs that I've made, and I'm thinking something softer is the way to go. I'm just trying to pick your brain a little if you've found something that you think will work well. Sorry for all the questions.

Thanks,
Brent

plazma

It's 2mm wetsuit neoprene with nylon on outer side and smooth surface inside.
This material was chosen for the prototype because it's easy to sew and glue.

Looking for cordura laminated PU for final version.

Here is a picture of the loop out of the casing. The lid will be replaced with one with a radial o-ring. The current lid leaks. The PC lid bends and only seals near the fasteners. This was expected and we tried this first because it's easier to machine.



-Pasi

plazma

Project update:

We had the fourth pool testing session today. Counterlungs are working ok. Dil and O2 bottless are in place. The device is starting to look like a rebreather

The breather is still a very unfinished proto. Many details will change. Many parts have been made "quick and dirty".

Next step is to start adding electronics. A simple triple PO2 display at first.

Pictures:
DIY rebreather

-Pasi