Pelagian MOD1 - done at last

wearypanda

Today I returned after a week on Koh Samui in Thailand completing my MOD1 on the Pelagian DCCCR with instruction from Andy Fritz, the man behind this excellent rebreather from Rebreather Lab. I spent time in the workshop helping to assemble my Pelagian, classroom time and then three days of excellent diving with Andy in the wonderfully warm sea. I even managed to see mystery shark, which I reckon is a Bull, but then I am certaily no expert.

The Pelagian is everything I expected it to be. It is extremely compact (the Meg looks huge alongside it). The Pelagian (without cylinders, backplate and wing) fitted into a hand baggage case (with room to spare) weighing around 14kg of which 2kg is the case itself. The engineering excellence and the thinking that has gone into the design in very impressive indeed. Out of the box the Pelagian gave me excellent trim thanks to the very small air cavities in the scubber head and the top mounted cylinder valves which, by the way, I found very easy to operate. As a real bonus I was delighted to be the first customer to have my Pelagian fitted with Rebreather Lab's new and very compact BOV.

I would like to say a huge thank you to Andy for his patience in answering my many questions, his excellent and thorough training and for the hospitality I was shown during my stay on Samui.

undrh2o

Any pictures of the BOV?

silent running

I would like to see a pic of the BOV too, I'm sure many would. Thanks for the report.

denka

He Andrew,

Congratulations on your MOD1 i have few questions,

How was the needle valve in action. Dos it need a lot of compensating in the deep or shallows.
Wat would you say about the two sensor set-up instead off three (kind off a principal question.)
How was the WOB compared to other rebreathers you have dived with

And a view pictures would be very nice!!!!!!

Groeten Dennis

wearypanda

Not brilliant pictures, but the best I could do for now. Measurements are:

• DSV 51mm square
• DSV and BOV combined, 90mm high, 83mm wide and 51mm back to front

These measurements exclude mouthpiece, BOV sensitivity adjustment knob and Bailout/Loop selection dial.











The BOV is very easy to use and breathes well. It holds negative and positive tests as well as a DSV by itself.

wearypanda

I will do my best to answer your questions. Please keep in mind that I am a complete novice so you my answers should be treated with the scepticism that my inexperience deserves.

The most straightforward way of setting the needle valve is to use flow meter to set a flow rate at just under your known metabolic rate adjusted for the maximum planned depth of the dive and then leave the needle valve alone. PO2 can then be adjusted as required using the injector.

Alternatively the valve can be set based on previous experience and potentially minor adjustments made as required during the dive to keep the flow rate as close as possible to your metabolic rate. For example, I worked out that a 1/2 turn open worked well for a 20m dive. Very little change is needed as depth changes and in fact I would say leave the needle alone until you have established at a step depth which you are going to hold for long enough to merit making any adjustment at all. The valve can of course be closed slightly as you descend and opened if your ascent is to be multi level and slow. This approach does of course demand especially close attention to your PO2, particularly on the descent, in case the adjustmnt you make results in O2 being injected as above, rather than below, your metabolic rate. In fact this seemed to be quite straightforward to verify once you have settled at a stable depth. Simply monitor the O2 readouts and you will quite quickly see if the values are increasing, decreasing or generally stable. This evaluation is helped greatly by the fact that the O2 readouts are to three decimal places.

So far as the 2 vs 3 sensor debate is concerned there have been plenty of threads about this already on Rebreather World so I will just relate my experience rather than mke any comments on teh relative merits. I concluded, after a lot of thought, that a diver controlled CCR does not really need 3 cells. This view is reinforced in the case of the Pelagian by the design of the head which give 'Instant Validation' of the cells without flushing the loop and wasting a lot of diluent. All that is required to do this is for you to breath out through the nose and then the next breath in, slow and long, to trigger the ADV which passes diluent directly over the cells giving you a PO2 value for your diluent. This enables you to easily and quickly verify which of your two cells is reading correctly should they diverge.

I chose to have a third cell to drive my VR3. This decision was driven by my desire to have an integrated dive computer basing its calculations on realtime PO2 values rather than my planned setpoint which, particularly whilst I am still learning, may not correspond precisely with my actual setpoint all the time. The fact that this also gives a third PO2 value to compare and contrst with the two on the main display is a bonus of course.

So far as WOB is concerned, I can only compare the Pelagian with a relatively short dive on an Inspiration Classic, so I do not have much to go on. However, my impression is that WOB was excellent and the curved counterlungs which follow the lines of the harness staps from shoulder to hips, mean that there is very much less change in WOB with changes in attitude. I find it difficult to believe that there is any system out there with better WOB. We were using DraegerSorb rather than fine mesh Sofnolime, so it is possible that WOB could increase a little using the finer mesh.

As you will have gathered I am very pleased indeed with the Pelagian. Choosing a CCR, particularly your first one, is a very difficult thing to do and required careful weighting of criteria. I actually put a deposit down on an Evolution initially, but decided after much thought that mCCR was a better option for me (safety record/diver involvement and simplicity/field serviceability). Once that decision was taken I ended up fairly quickly with a choice between the COPIS Meg and the Pelagian. There were several reasons why I went down the Pelagian route rather than go with the Meg. I am delighted, particularly having now seen the two CCR's side by side, that I have made the right choice - for me.

And just one more picture. You will of course see that I have a stage/bailout cylinder. No problem at all with the counterlungs. And with an ali backplate and a 3mm full I needed just one 2lb weight.

silent running

Thanks very much for the pictures and detailed report. I have some more questions about the unit which hopefully you or Andy can answer:

Do you know the internal diameter of the BOV, what kind of flapper valves and what kind/brand of 2ndstage is used in it?

I think I remember hearing that the BOV barrel doesn't have any o-rings, is this right? If so, how long is the life of the barrel before it cannot seal properly because of sand/grit scoring the surface? How often will it have to be rebuilt?

Thanks, -Andy

wearypanda

I will leave it to Andy to tell you what valves and 2nd stage internals are used. However, I can tell you that the barrel does have o-rings, so your concern over scoring is unfounded..

Actually, I am pretty sure I recall Andy telling me that at least part of the 2nd stage in the BOV is from a Scubapro S600. I will lave Andy to clarify that in due course.

fredrik

Can we also have pictures from the mouthpiece side and when it´s turn upside down?

__________________
Fredrik
Rekodeko, Sweden
http://www.rekodeko.se

wearypanda

These have been added to my posting above.