Hey all,
When this thread first came out, I was fairly "OK" with some mixing and matching, but definitely agreed with JonT's feelings. Still, there was just something that gnawed at me. I had heard rumors to the contrary that were never substantiated. Consequently, I did some research and found out a few things I didn't know before...
Not all second stage regs use downstream valves. Most notably the Poseidon regulators use an upstream valve assembly. So, if there is a free flow from the HP seat on the First Stage, there HAS to be a way to release the pressure build up in the LP hose which is normally just vented in the downstream design. Unfortunately, the OPV (Over Pressure Valve) is built into the First stage on many of the Poseidon systems. Consequently, putting a Poseidon Second Stage on any other First Stage without fitting it with the OPV can be dangerous. It could result in splitting the hose or exploding the Second Stage in the Divers mouth. However, you could put just about any Second Stage on a Poseidon First Stage. The additional OPV will not affect performance.
Also some First stages are tuned to have a higher IP (Intermediate Pressure) than others. While these can be de-tuned to lower pressures, they were not designed for that and this may cause performance problems. These pressures also greatly affect the cracking pressure needed on the Second Stage, which is why with ANY FrankinReg, you should have a qualified technician check it out. Or at least learn to do those procedures yourself!
Dont get me wrong
I own two FrankinRegs. They are the old Aqualung Second Stages on Poseidon First Stages. A good friend of mine sold them to me, and I am glad he got it right. As for OPVs, you can buy them to screw into any of the LP ports of your First Stage. People who use a dedicated reg to run argon in their drysuits use them a lot.
