Question 1st stage recommendation for use with FFM and conventional 2nd stage

[NGriff77]

Hello!

I switch between diving an integrated full-face mask and a regular mask + second stage. I’m looking for a new 1st stage that can mate well with both configs. Key requirements:

• has user-adjustable intermediate pressure — needs to be tunable between 135-145psi
• cold water tolerant
• nitrox compatibile

Recommendations for a trusted first stage would be much appreciated.
Thx

 

[lexvil]

For that adjustment range, just about any diaphragm first. Do you want or need a LP port to swivel?

 

[NGriff77]

Thanks @lexvil. Probably should have stated my requirements more precisely. I'm looking for a sealed diaphragm 1st stage that will maintain a very stable IP within that range. The FFM I use is the Neptune III by Ocean Reef. They specify between 138-142psi. I've struggled a bit with free-flow mid-dive. My idea was that if I could narrow down the IP range, this should improve the performance.

 

[lexvil]

Thanks @lexvil. Probably should have stated my requirements more precisely. I'm looking for a sealed diaphragm 1st stage that will maintain a very stable IP within that range. The FFM I use is the Neptune III by Ocean Reef. They specify between 138-142psi. I've struggled a bit with free-flow mid-dive. My idea was that if I could narrow down the IP range, this should improve the performance.

There are a lot of options, Zeagle DS type can be found at great prices same with Flat Head 6 firsts. SP MK 17, Deep 6, HOG etc. a lot of choices and they are all easy to adjust the IP on.

 

[NGriff77]

Longevity of the SP MK11/17/19 line puts it near the top of my list. I’ve read in other threads that the MK17’s IP can fluctuate by 10psi during a dive. Don’t have a sense for whether that metric is good, bad or ugly. Clearly I need to read up on intermediate pressure and how much drift is considered normal.

 

[rhwestfall]

@lexvil just posted an SR2 first and second for a great price. That dry sealed piston first is a piece of genius...

 

[lexvil]

@lexvil just posted an SR2 first and second for a great price. That dry sealed piston first is a piece of genius...

Can’t adjust the IP

 

[DeepBlueDog]

Hello,

I have a follow up question regarding the Neptune III. The first stage that OR bundles with the mask has a flow rate of 4800 L/min or 171 cfpm. Why such high flow rate? The accepted maximum RMV for heavy work is 100 L/min so at a depth of say 50 m that 600 L/min which is only 21 cfpm. The flow rate of OR first stage is 8 times more than the maximum required. Even considering a 20% overhead that is much more than would ever be needed unless one has multiple octopi hanging off the same 1st stage being used all at the same time. What am I missing here???

 

[lowwall]

You should take a look at any of the current generation of Mares first stages with a TBP cold water environmental seal kit. The 82X and 28XR have a turret if that's a requirement.

Mares diaphragm regs dating back to the original MR22 (aka Abyss) have always been noted for maintaining a very stable IP over a range of tank pressures. It's something they concentrated on since they used to only offer unbalanced seconds stages, so a stable IP was crucial for consistent performance.

I got a DM from @rsingler a few weeks ago about this:

"Just picked up an 82x + TBP add-on to play with,
and as you recommended, a 28XR + HR-XR 2nd.

IP 145 and ZERO IP shift from 2600 to 300 psi.
Impressive."

They are also all EN250A rated and meet NORSOK U-101 requirements at 200m, so can easily handle high flow rates which it appears your mask requires.

 

[DeepBlueDog]

I have asked OceanReef about compatibility of Neptune III with Apeks DS4. Here is their reply I just received:

Regarding your kind question, I can confirm that there will be no problem using the Neptune III mask with an Apeks 1st stage.

Our masks are designed to work with first stages that deliver an intermediate pressure between 9 and 10 bar, as is the case with the Apeks DS4.

As far as I know the flow rate of DS4 is around 72 cfmp but it does have the pressure required. Same goes for XTX200 fsr. So it seems one doesn’t need a high flow 1st stage. Which still begs the question why does OceanReef offer such high flow rate. And also why would any 1st stage have a high flow rate? What is the benifit of high flow rate? My other reg is Poseidon Xstream and that is 5000 L/min but the pressure is 8.5 bar so no good for OceanReef.