Pelagian/Voy Oxygen addition

mattarte

From my understanding, both use depth compensated regulators and a needle valve. Speaking only of the Oxygen addition, are there differences in these two systems?

Rebreatherlab

That is news to me. I had some guys who used to dive the Voyager and claimed that they used blocked first stages on it. Maybe a new version uses depth compensating? If so I guess the comparison would be in the CV factors and flows of the needle valves, 1st stage recommended IP+type of 1st stage and the reliability in the contruction of the manual O2 ad valve.

Best to check straight with Voyager people.

cheers,

Andy

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dave t

I saw the new voyager a couple of days ago and it does use a normal compensating first stage but no needle valve. The flow is set before diving and as far as I could see is not adjustable once underwater. Aledgedly the flow remains stable even though the IP increases!!

Dave

gibbogeo

The voyager, from his first appareance as a prototype, is using a normal first stage without any sealing that change the IP with the depth.

It does use a needle valve that the user preset at surface and can't adjust during the dive.

The IP of the first stage is normally set to +4 or +5 bar and the flow is usually set quite low (0.5) at surface.

I tested the voyager needle valve personally with a first stage that can change the IP, two pressure gauges, one additional needle valve, a bucket of water and a flow meter.

The result is that the flow of oxygen increase with the depth.

I made a test with the same setup using with a Kiss valve instead of the needle valve and the flow didn't changed until the ip was more than 2 time the pressure after the orifice, then started to decrease, according to the theory.

If someone has a swagelok needle valve with 1/4" tubing connection for sale at very low price, i am interested to buy it, to check it with the same setup.

dave t

yes, sorry when I said no needle valve I meant one you could adjust underwater like the Pelagian.

The guys who dived it said the po2 remained very stable shallow or deep and didnt notice any creep upwards.

so is the little "box" just a needle valve, a manual button and some offboard connectors or is there something a bit clever inside?

Dave

mattarte

Thanks everybody for the answers. So the mechanical difference is the underwater adjustability of the needle valve. Speaking of the uw adjustable needle valve, unintentional adjustments (eg. sliding against other objects) are a considerable risk?

Rebreatherlab

We put the needle in between the in and out hoses which are of larger diameter than the needle adjustment handle. If you would scrape the whole assembly, say against a cave wall, you would rather get some scratch marks on the hoses than accidentally turn the needle. If you scaped it against something sharp, protruding from somewhere you might, (if you are extreemely unfortunate), turn the needle max half a turn. This would represent a flow shift of maybe 0,3 lpm, so if you check your Po2 every 5 minutes it may have gone up or down a bit or maybe taken out by increased work or vice versa. In short; no big drama.

I also like to wedge the Po2 meter in between the in and out hoses of the needle block. That keeps the block in front of me and keeps the Po2 meter like a rear view mirror so I can check Po2 hands free. The Po2 meter sticks out in front of the needle block and would likely take the first bounce, my forehead the second. Have a look at my avatar and you will get the idea.

If what Giggebo writes is true it seems like the Voyager uses the same system. If they use a low IP like 5 BAR it means you get more flow increase with depth. With an IP of 9 BAR, our orifice and our needle you get 1% massflow increase per meter to 90 msw. After 90 msw you get increasingly less increase per meter as the flow goes subsonic. As temperature comes into play the sum total O2 dosage increase of 1% per meter is about right down to 300 m.

In essence you could use the Pelagian block the same way as the Voyager, meaning you set a surface flow that becomes suitable to your planned max depth and then you dont touch the needle during the dive. Just ad a bit more frequently with the bypass O2 ad valve during the ascent.

This is the way we teach it during training in order to get the basics down. After a few additional dives most students like the idea of being able to adjust during the dive.

All the best,

Andy

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mattarte

Got the idea. Thank you for the clear answer.
Cheers

gibbogeo

This is really interesting, because lot of people that i know say the same thing.

Also people using a swagelok micrometric valve with a normal first stage are ready to swear that there is no bigger flow with the depth.

Mi plan for the next test is to go at 40 meter with a one liter bottle and a needle valve, open the gas for 10 minutes, note the difference on the spg, close, then do it again at 30m, then 20m and so on to the surface, to convince the friend who tested with me the flow that there is a variation with the depth, because he is still not convinced.

The clever part of the needle valve is that have a double diameter, thinner at the tip, biger at the base, so can be used to adjust a smal flow (for CCR) and a bigger flow (for SCR).

But no magic to maintain a a flow with the IP augmenting.

dave t

Cool, please let me know the findings of your experiment

Dave