Mixing different brands of octo/2nd stage

[parheric]

Just wondering, whats the deal with having the same brand of octo and 2nd stage. Is it really an issue? or is mixing any octopus/reg fine so long as all your hose connections all fit nicely and don't leak?

 

[loosebits]

Basically, yes but you will want to tune (or detune) the octo to deal with the possibly different IP of the mismatched first. Second stages are always tuned to perform as you want based on the first stage's IP. For a primary second stage, you probably want it tuned to the edge of freeflowing, for a seconday 2nd stage (octo), you want it backed off a bit. If your octo is expecting an IP of 140 psi from the 1st stage and it's getting 150, it's going to breath a little too well and will probably free flow on you.

 

[miketsp]

The other thing to watch out for are overbalanced 1st stages. In combination with some 2nd stages you may get a free flow at depth.
An overbalanced 1st stage presents a diaphragm with a larger area to the ambient pressure than that used to transfer the pressure internally. So the IP differential over ambient will actually increase as you descend.
It's generally easy to identify an overbalanced 1st stage from the advertising literature or the user manual.