AquaPix:
Maybe mixing different brand regs is not such a good idea. There are no official tests done with different brand regs and therefore no CE approval. To combine them is actually easy as most regs got the same threads, but this is where the similarities end. There are different intermediate pressures in the first stages of all brands and this alone can make it impossible for you to adjust and fine tune second stages that you screw into the first stage and I don't even want to start with the different flowrates. Also, please ask yourself if you can trust your regs to work in any condition. What can go wrong will go wrong, it is just a matter of time. If you don't get a problem underwater then you will run into a big one the first time when you need to get them serviced. Apparently it is against HSE rules and regulations to sell or service regulators that are assembled with different brand parts and the service centre can be prosecuted.
Let me tell you another story that just happened to me 2 weeks ago in Dahab (Egypt). I went there with a couple of friends to do some trimix diving at the Blue Hole.
When we prepared our equipment a friend of mine assembled Apeks first stages (sorry don't remember which ones) and Scubapro (S600/R390) second stages. His instructor pointed out the problem that could arise from such a combination and told us the HSE story. The instructor should know as he owns one of Londons largest diving schools. But stubborn as my friend is he wouldn't change his reg configuration. End of story? ... he nearly killed himself! At his last dive into the Blue Hole he suddenly got a severe freeflow on his primary reg (S600) at 100m and couldn't shut it down himself. Thank god his instructor reacted quickly and managed to control the situation.
OK, this example is a little bit extreme and some of you might argue now that the average diver will never go to these depths, but do you know which problem can arise from coupling different brand regs and when and where you will run into difficulties.
Please ask yourselves if you want to risk your life (and maybe the one of your buddy!) over such an unneccesary experiment.
Cheers, Andy (AquaPix)
There are a few regulators (Such as Poseidon and some sherwood regulators) which operate with a higher interim pressure than normal, but to my knowledge, Scubapro, Mares and the other big regulator manufacturers operate with an interim pressure of 10.5 bar. Apex has a peculiar one where the interim pressure increases relative to the water depth - Not sure how that would affect it, so I would check that with a service technician before I combine Apex with anything else. I expect the result would be that the relative pressure on the second stage would remain 9-10 bar, regardless of depth (So for all intents and purposes, just a balanced regulator) but I'm not entirely sure, so I'll leave this one to people knowing the apex's better than me.
Also remember that since Aqualung bought Apex, Aqualung regulators are pretty much the same as the Apex's.
For the other manufacturers, you can interchange the second stages (as long as the threads match). Best way to make sure though is to buy an Interim Pressure Gauge (Which plugs in to your low pressure hose), and check that both first stages have a similar interim pressure. (as in within .5 of a bar.)
If the interim pressure is higher, you should reconsider, or if you choose to go ahead, detune the second stage to avoid freeflowing. If it is too low, it just means you'll have a heavy breathe. (Which, on deep dives can be very dangerous, so do be careful)
Aquapix: If your friend couldn't do his own shutdowns, then IMHO he had no business doing a deco dive to 100 meters in the first place. All the tech training agencies I've looked at has emphasised shutdowns heavily during the deco procedure training. Not being able to do the shutdowns don't sound like mastery to me.
E
