How often should I even service my regulators? I do about 70 dives per year currently. By service, I mean replacing everything that comes with the service kit.
You will hear wildly different opinions on this. Extremes range from every 6 months to only when something starts to go wrong. The truth lies somewhere in between and you should service the regulator so that you are comfortable diving it.
Expanding on the above, do the HP valve, both diaphragms and the conical filter need to be replaced every time?
Again, you will hear wildly different opinions on this. I don't see anything wrong using a sintered filter forever, as long as it has not seen a dirty environment. This can easily be seen with the naked eye or simply trying to breathe through when removed from the regulator.
I won't comment on the diaphragms and HP seat, as again opinions differ wildly. For what it's worth, Apeks would like you to replace them on your service.
Does anyone know from what material (and hardness) is the internal diaphragm? I presume the external (hydrostatic) one is from silicone.
The internal diaphragm is nothing I would cut out of a piece of other material you have lying around. These are not made of one material, but they have a woven mesh sandwiched between two layers to give it extra strength. You can surely find aftermarket replacements, but I don't think you can simply make one yourself.
The environmental seal on the other hand is made of one material. Even if you mock something up here it's not the end of the world, say if the outer diaphragm ruptures or tears. It must of course be flexible enough to allow for transmission of pressure differences.
Am I correct in buying EPDM o-rings? I am only looking to use the regulators with up to 40% nitrox.
Again, this is something of a heated topic among divers. For what it is worth, take apart some medical equipment and you'll be hard pressed to find EPDM o-rings. Most of the time it's cheap NBR. That being said, you are likely wise to stick to more flammable resistant materials as NBR.
Go with what the manufacturer has put in there, as different materials have different characteristics with regards to friction, extrusion resistance, etc.
I can source most of the parts locally except for the HP valve and the conical filter. Does anyone have a source for those at a normal price (possibly EU)? The easiest for me is to simply buy from scubagaskets.com but the HP valve price seems quite high for what I get.
Watersafetyshop.eu will likely have some of the things you are looking for. I'd be buying full kits, as it keep the headache to a minimum.
Arcus has virtually any o-ring / sealing surface you could ever want.
Both of these sit in Europe, specifically Germany.
is there any practical difference in using EAN40 vs. EAN50 from the regulator's point of view?
The higher the O2 %, the higher the ppO2 will be that the parts are getting exposed to, so yes it does make a difference.
The current consensus in the SCUBA industry is to treat anything above 40% O2 like 100% O2. If that makes sense or not is of course debatable. I imagine looking back in a decade or two, the whole thing will look very similar to the "Nitrox debacle" of old, where the gas was demonized.
If you keep things clean, and I want to emphasize
keep clean, you will not have any trouble with high O2 percentages. A once off super duper cleaning is much less efficient than servicing the gear regularly and keeping it clean.
Use what the manufacturer currently recommends. This will be easy to source and safe at the same time.
Viton o-rings are required in that case?
Viton does not equal Viton, there are several grades of this material, which in general is called FKM or FPM. The advantage of FPM over say NBR or EPDM is the temperature it can withstand. The main advantage of FPM over NBR or EPDM is it's resistance to solvents and petroleum, which really has nothing to do with the diving industry.
EPDM can withstand 100°C up to 140°C, depending on how it was manufactured. NBR should only be used up to 100°C. FPM, or Viton as often called, can withstand up to 200°C or 210°C.
This slight increase in temperature resistance can be beneficial in parts that see high ppO2, which is only parts of the first stage that also experience adiabatic heating. The main part you should be thinking of is the seat of the first stage, as this is one of the parts that tick both boxes from above. It is crucial that this part is fit for the purpose of high ppO2 environment. Manufactures usually have seats that are made for this.
You may find the attached service manuals helpful. Even if dated a little, nothing really has changed.
