Do you know the duro for AP1166? I use viton duro 90 caz what's what I got in the kit.. and have to replace them quite often as they simply deform and lose the round cross section.
Viton, which is just ex DuPonts marketing name, is better called FKM (Fluorine Kautschuk Material). It has a few great characteristics which speak for it.
- A great temperature range, it can operate in -30°C to 200°C.
- A high resistance against mineral oils, aliphatic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons, acids and alkalis.
- A very low gas permeability
The above are of high importance in a lot of industrial settings. But none, besides it's temperature range, are of any interest in SCUBA. And there only with regards to ignition points and O2 usage.
FKMs usually do not have better mechanical properties than cheap NBR. Their abrasion resistance is on par with NBR and compression set is only slightly better. FKMs do have a much better ozone resistance than NBR, which is about the only thing of interest in your specific case. That AP1166 O-Ring is exposed to the environment extensively.
ScubaPro got it right with their choice of PU (Polyurethane) for this O-Ring. PU has one of the best abrasion resistance and short term resilience that you can currently find in an O-Ring material. It has a horrendous compression set, which is of no interest if you don't plan to keep your regulator attached and pressurized for a week or so. PU has better mechanical properties than EDPM, FKM or NBR with one of the best ozone resistances (At least on par with FKM). In fact it has one of the best abrasion and short term set resistances of all o-ring materials I know of.
PUs shortcomings are of no interest for the diving industry, which would be:
- Temperature range of only -35°C to 80°C. The material can be adjusted for slight increases in both directions. Despite this low temperature range, it is commonly used in industrial O2 settings. The low ignition point must be taken into account.
- Low resistance to ketones, acids, chlorinated hydrocarbons, brake fluids, etc.
- Terrible compression set
For the AP1166 O-Ring from Apeks, which is a BS1806 111, I can not think of a better suited material than PU with a 90 or 85 durometer. In fact Scubapro uses 85, not 90. If you get one of these O-Rings, it is likely going to last you for a couple of years, even with heavy use.
I do want to retract about what I said earlier about Apeks using 80 EDPM for most/all O-Rings. I have scoured all the documentation that I have and I think this is rather unlikely. ScubaPro for example uses o-rings with 50, 62, 70, 80, 85 and 90 shore. For materials they use EDPM, FKM, NBR and PU. Given this wide range I find it
not very likely that Apeks would just use a 80 EDPM for everything.
I was likely wrong when saying so and relied on convential wisdom.
TL.DR: For your AP1166, get a BS1806 111 made from Polyurethane (PU) in 85 or 90 shore. You'll be needing very few replacements.
