Poseidon Xstream free flow

[CaptainHornblower]

Yesterday at the end of a dive my reg and alt (both Posiedon Xstream) started free flowing. We were just about to surface, I was probably 4 or 5 feet down, tank pressure was down to about 600 psi and away they went. I surfaced, manually filled my BC and had my buddy shut the tank valve. My computer said the pressure at the conclusion of the dive was 22psi. The regs worked fine during the dive up to that point.

Any thoughts or similar experiences? I had the regs serviced about 5 dives (and a year) ago.

 

[tfsails]

Since the Xstream is an upstream second stage, it needs a certain intermediate pressure to work right. Usually this is about 120 psi if you're using the Xstream first stage. If you let your tank pressure get lower than that the second stages don't have enough pressure to seal the "balloon" and prevent free flow. What happened to you is entirely normal. If you were to go put your reg on a known full tank I'd bet a beer that it would work properly.

We've experimented with this exact scenario at out dive shop's service center and found that if you let tank pressure get too low on Xstreams and Jetstreams you get a free flow.

 

[Puffer Fish]

Humm, interesting. Think we are missing some key information, but given what what provided, it is easier to tell what it is not:

If my memory still works, the Poseidon has to have an over pressure valve, in case the first stage were to fail, as the second stage would not just start free flowing. So that rules out overpressure as an issue, and besides, once the tank got below the intermediate pressure, the regs would have stopped )which they did not.

So if it was not the 1st stage being high, could it have been the first stage being low? Never seen or heard of that, but if it was not the first stage, then how could both regs free flow at the same time.

So, did they both start at the same time? Or did one start, then when you switched to the other, it also did it?

Was this cold water? Fresh water?

I have never used one with a tank below say 150 psi, but would not be surprised if they did that. But that would mean you were actually lower than the 600psi...

 

[Puffer Fish]

Since the Xstream is an upstream second stage, it needs a certain intermediate pressure to work right. Usually this is about 120 psi if you're using the Xstream first stage. If you let your tank pressure get lower than that the second stages don't have enough pressure to seal the "balloon" and prevent free flow. What happened to you is entirely normal. If you were to go put your reg on a known full tank I'd bet a beer that it would work properly.

We've experimented with this exact scenario at out dive shop's service center and found that if you let tank pressure get too low on Xstreams and Jetstreams you get a free flow.

That was my guess, so thanks for actually knowing that.

Which now leads to why he thought it was at 600 psi... wonder what is not working there?

 

[scubafanatic]

Since the Xstream is an upstream second stage, it needs a certain intermediate pressure to work right. Usually this is about 120 psi if you're using the Xstream first stage. If you let your tank pressure get lower than that the second stages don't have enough pressure to seal the "balloon" and prevent free flow. What happened to you is entirely normal. If you were to go put your reg on a known full tank I'd bet a beer that it would work properly.

We've experimented with this exact scenario at out dive shop's service center and found that if you let tank pressure get too low on Xstreams and Jetstreams you get a free flow.

Yes, this is correct, my older Jetstreams to the exact same thing, for the exact same reason, if memory serves, I remember it happening at about 300 psi on mine, however, unlike the Xtremes, the older Jetstreams have a 2nd-stage '+'/'-' detune switch, so I can lower the psi point at which the freeflow will happen somewhat if I switch it to '-', but the freeflow will still eventually happen....which is one reason I don't really dive my 'Jets' any more.

 

[CaptainHornblower]

To fill in the details, they both started at the same time, I was breathing the primary when they started free flowing. I was in salt water and the water temp was about 75 (I'm in Maui, HI . I'm pretty sure about the pressure; my wife and I were within about 100 psi when we checked just a few minutes before the end of the dive; her Oceanic ProPlus 2 said she ended up with 550 psi (I was using an identical computer). So I think that's about where I was when the regs started free flowing and basically drained my tank. I assume this is something the tech would have adjusted when he serviced the regs. Is this something he could have set incorrectly?

 

[CaptainHornblower]

Also, at the begining of the dive both of our computers read in the 2900 psi range, which was consistent with freshly filled tanks.

 

[Puffer Fish]

To fill in the details, they both started at the same time, I was breathing the primary when they started free flowing. I was in salt water and the water temp was about 75 (I'm in Maui, HI . I'm pretty sure about the pressure; my wife and I were within about 100 psi when we checked just a few minutes before the end of the dive; her Oceanic ProPlus 2 said she ended up with 550 psi (I was using an identical computer). So I think that's about where I was when the regs started free flowing and basically drained my tank. I assume this is something the tech would have adjusted when he serviced the regs. Is this something he could have set incorrectly?

A bit, yes. But I would test the reg first. From memory, it should be happening when the intermediate pressure drops, which I would expect to happen around 200 psi. As I never went that low on a tank, have never actually seen it in real life.

Would be very interested in know at what pressure that happened.

 

[scubafanatic]

While I'm not an expert on the Xtreme, they work the same way and the older 'Jetstreams', the 2nd-stages have a little balloon/condom 'thingy' inside that inflates and will deflate if the reg is de-pressurized, or will deflate (causing the freeflow) if tank prssure drops too low. The only way I was able to reduce the sensitivity 'in the field' was to detune the 2nd-stage via the '+'/'-' switch, the negative consequence of switching to the '-' position is increased breathing resistance, not too big a deal on a Jetstream and I only 'flip the switch' near the surface at the end of the dive anyway. However, as the Xtreme has no such 'switch', the solution might turm out to be for the tech to reduce the sensitivity by 'permanently' detuning the reg, and you'll just have to live with a higher breathing resistance during the dive......which was another reason I stayed with the 'Jets' and wasn't interested in the non-adjustable Xtremes...the boats I dive off of in the Flower Gardens will bench a diver for running out of air, not to mention running out of air is a bad thing anyway.

 

[CaptainHornblower]

the boats I dive off of in the Flower Gardens will bench a diver for running out of air, not to mention running out of air is a bad thing anyway.

So I would have been ok - I had 22 psi left