Mixing First and Second stages from dif manufacturers

[Mike1967]

Might be better off just getting the apex sidemount set.

This ^

 

[Rose Robinson]

since xstreams 2nds are upstream regs, that means they fail closed right? on the appropriate first stage, the OPV allows the first to bleed extra pressure. What happens if a first stage with no OPV has a freeflow from freezing open, and the second stage stops delivering air instead of freeflowing? does the hose explode or something?

Yes!

That is the problem.

Older Poseidon Regs, had the OPV in the hose on the second stage end.

The problem with this hose was that some felt it was expensive, but the primary issue was that not all shops kept them.

The new GEN Poseidon systems have the OPV in the 1st stage, allowing owners to use standard LP hoses.

Rose.

 

[SlugLife]

I am putting together a sidemount set and the DGX sets include a Poseidon Xstream set but they do not have rotation or 5th on the 1st stage. I was thinking of running them off of DiveRite XT1 din 1st stages. Can I have my LDS tune this setup to work or should I not mix them. I have been running XT2 regs off of them but would like to upgrade the 2nd stages and have the benefit of breathing off either side.

Broadly speaking "pressure is pressure" so long as we're comparing "balanced" regulators, and the same IP. Your 1st stage will typically bring the IP ("Intermediate pressure") down to about 140psi, which then the 2nd-stage brings down to about ambient-pressure.


There are some nuances though, such as what your 1st stage IP is. I'd probably be fine with mixing brands, so long as I did a practice dive with redundant air and verified it breathed fine at depth.

 

[Bald Wookie]

Broadly speaking "pressure is pressure" so long as we're comparing "balanced" regulators, and the same IP. Your 1st stage will typically bring the IP ("Intermediate pressure") down to about 140psi, which then the 2nd-stage brings down to about ambient-pressure.


There are some nuances though, such as what your 1st stage IP is. I'd probably be fine with mixing brands, so long as I did a practice dive with redundant air and verified it breathed fine at depth.

Mostly true, but I'd advise reading the above about upstream and downstream regs

 

[JLHNova]

Property 1st stage Setting SI units Setting common units Setting US units P1 30 MPa 300 bar 4351 psi P2 >750 kPa > 7.5 bar >109 psi P3 2 MPa 20 bar 290 psi P4@p1, P4@p3. 800 – 1100 kPa (unadjustable) 840 – 860 kPa (adjustable) 8bar - 11bar (unadjustable) 8.4bar - 8.6bar (adjustable) 116 - 160 psi (unadjustable) 122 - 125 psi (adjustable) P5 >750 kPa > 7.5 bar >109 psi i +/- 110 kPa +/- 1.1 bar +/-16 psi R max 100 kPa max 1 bar max 15 psi Q 0.12 m3 /h 2 L/min 0.07 ft3 /min Internal leaktightness 12 ml/h* * Corresponds to a pressure climb of 0,01 bar/ min for a regulator with a 70 cm hose. Property 2nd stage Setting SI units Setting common units Setting US units CP (cracking pressure) 274 Pa to 392 Pa 28 to 40 mm.w.c 1.1 to 1.6 inch of water
Normal interstage pressure 123 psi

XT1 intermediate pressures recommended at 140psi in service manual

I am not sure having read both haha. I am def not a reg tech.

I've been diving since 1968.I used to here horror stories about mixing different brands. But for the last 30 years I've had about every different combination of stages you can think of. Poseidon Jetstreams need an overpressure relief. But any thing else will work, you may need to adjust the IP.