1st stage for cold water

[amaiel]

We had some problem (icing and subsequent free flow) last winter with the MK20 becouse of cold water and we want to replace all our 1st stage (back gas).

In the last weeks I have been testing the poseidon 1st stage coupled with a G250, metal barrel, IP 10 bar. And it works great.

Now it's time to decide, which diaphragm 1st stage?

Some info:
temp. often < 40 F, cave diving with mix gas, we would like to maintein our second stages (G250 and scubapro adjustable, they still work very well), hogartian configuration.

We have two otions at the moment (open to evaluate other, oc)
- Posidon first stage
- ATX 200 first stage
Both seem great first stages, price is almost the same.

What do you think about the choice? Servicing? Routing? Other info?

Thanks in advance for your help

 

[rescuediver009]

I would go for the ATX200 first stage. While the poseidon is a diaphragm and will fuinction alot better than the Scubapro in cold water it is not sealed. I think that the Apeks sealed system will perform the same and it is sealed and offers parts for life over the Poseidon.
Also too, the Poseidon upstream design will create problems with the mixing of a non-servo-assisted second stage. I am sure you are aware that the IP increases as the tank pressure decreases resulting in an increadibly detuned second stage. Not something I would want to take into a cave with me. Not to mention what the hogarthian gods will think of you on judgement day.

 

[Quarrior]

The Apeks is a great reg. Another one to look at since you opened that door is the Zeagle DSV with the ZX second stage. Don't foreget, whe looking at cold water regs, your second stage is just as important as the first stage.

 

[amaiel]

...
Also too, the Poseidon upstream design will create problems with the mixing of a non-servo-assisted second stage. I am sure you are aware that the IP increases as the tank pressure decreases resulting in an increadibly detuned second stage. Not something I would want to take into a cave with me.....

That's true, but amusingly we have not seen difference in the regoulator performance using the SP 2nd stages (g250 and adjustable) even with 50 bar (but please, don't ask me why).

What do you think about the routing? With the tx100 was pretty hard to find the right routing.

Thanks

A.

" Not to mention what the hogarthian gods will think of you on judgement day."

ps paraphrasing one of the Hogartian fathers ... work what works

 

[DA Aquamaster]

That's true, but amusingly we have not seen difference in the regoulator performance using the SP 2nd stages (g250 and adjustable) even with 50 bar (but please, don't ask me why).

The G250 uses a balanced poppet with only a slight downstream bias so a change in IP will have very little effect on the cracking effort of the second stage. When this is combined with the adjustable feature of the reg and proper tuning, there will be no difference in cracking effort at full and near empty tank pressures.

With the Adjustable second stage, the cracking effort is again "adjustable" and if properly tuned can compensate for the increase in IP. But the adjustable is also readily converted to balanced adjustable status where it essentially becomes a metal cased G250. Consequently, there are very few honest to goodness adjustables still floating around out there in regular service. The poppet and balance chamber required for the conversion come in the G250 annual service kit and the new spring that is required costs about $1.00.

Assuming you have access to Scubapro dealers, you may want to consider the Mk 16 or Mk18. It is not a sealed diaphragm design as the ambient chamber is open to the surrounding water but it is thermally protected and there is so much water flow in the ambient chamber that the heat transfer makes freezing virtually impossible. We have not been able to freeze one up on local ice dives.

 

[amaiel]

The G250 uses a balanced poppet with only a slight downstream bias so a change in IP will have very little effect on the cracking effort of the second stage. When this is combined with the adjustable feature of the reg and proper tuning, there will be no difference in cracking effort at full and near empty tank pressures.

......

Assuming you have access to Scubapro dealers, you may want to consider the Mk 16 or Mk18. It is not a sealed diaphragm design as the ambient chamber is open to the surrounding water but it is thermally protected and there is so much water flow in the ambient chamber that the heat transfer makes freezing virtually impossible. We have not been able to freeze one up on local ice dives.

Thank you a lot for the explanation. Very clear.

You didn't consider the poseidon. Can I ask why?

Considering the 3 options (Apeks, SP, Poseidon) which would be your choice?

We have easy (and cheap) access to all the 3 brands.

Thanks

 

[DarkFrog]

The Apeks is a great reg. Another one to look at since you opened that door is the Zeagle DSV with the ZX second stage. Don't foreget, whe looking at cold water regs, your second stage is just as important as the first stage.

So for cold water regs, you want the first stage sealed, in order to keep water from getting in and freezing up the works. But how do you evaluate a second stage's appropriateness for cold water?

-Justin

 

[Bob3]

Which model Poseidon, the 3790 (Jetstream) or the Xstream?

You didn't consider the poseidon. Can I ask why?

There *might* still be some anti Poseidon bias left over from when a very "non-responsive" US distributor was handling the Poseidons.

 

[amaiel]

Which model Poseidon, the 3790 (Jetstream) or the Xstream?

I'm using the jetstream for the test and it seems to work great with our second stages, just fine tuning the IP. Tested in 50 F.

 

[Bob3]

You may want to add the antifreeze cap then, it'll be good to 28°f.
The Xstream has an impressive thermodynamic heat sink, but it cost like $90 more than the 3790.