Quote: (Originally Posted by
paulraymaekers)
hello all, as a test, since a year some of us are using luxfer carbon full wrap tanks on their breathers: they are great for traveling: a 3l tank weights 1.9kg! but....
they are not rated for diving, only for SCBA. the explication I got is that there is not enough market for those little lightweight tanks to go trough the testing and certification proces for diving application.
are there other reasons why?? I heard of the dräger composite tanks that could not be used for diving because of porosity in seawater, but I think this does not apply for the luxfers w're using.
any idees???
paul
Hi
Do you know if Luxfer are making the cylinders or if the buy them from some other manufacturer? I know that Interspiro composite cylinders are made by a ABB company.
I have dived with Interspiro composite twins on OC, and happened to teach a dive course for the company. So I picked up some info about some problems with composite cylinders in SCUBA applications.
Have you noticed that the cylinders drop in pressure if filled and not used for a few weeks? Gas is lost by diffusion.
If no, then you probably have a cylinder with a metallic liner? As I got it the liner can be a dangerous thing since the thermal expansion will likely not be the same as the composit and this can promote the formations of cracks. So cylinders with a liner might needs special inspections/handling procedures. I got that info from Interspiro and they don't use metallic liners so the information could be biased.
The testing for SCUBA approval of a composite cylindes is much stricter than for ordinary cylinders, the same goes for the inspection interval/procedure. This is due to several complications like that the material is much easier to damage, water affects the composite in several ways, the fabrication of the cylinders have a higher degree of defective units.
The seal between the valve and the cylinder is also a critical part since its metall to composite. The expected corrosion of the metal insert (valve to cylinder) and swelling of the material can be very different for a SCBA and SCUBA case. So a SCBA design may be unsuitable and dangerous for SCUBA.
Use of higher O2 contents can also be a real problem for composite cylinders. Interspiro is delivering composite cylinders that are approved for SCUBA with _Air_ to the Swedish Navy for use in semiclosed _nitrox_ Rebreather. But these are not really approved for general nitrox use since (if I got it right) the composite has properties like ignitions points that are too low. The Navy got around this since they can approve things for internal use according to their needs without having to follow EU rules and such things. But (again, if I got it right) they did alot of testing and found them to be safe for _premixed_ nitrox filling but _not_ for 100% O2.
So, lots of potential troubles.