Rebreather try-a-dive (Pete Readey Thread)

[Pete Readey]

Oh! I nearly forgot, CO2 permanently damages sensors.

Also, do the batteries in your unit off gas as I remember them being in the breathing mix? Also some cleaning agents can cause problems at elevated partial pressures?

Unfortunately no not Stargate in the Bahamas just cold water Baltic, North Sea, Irish Sea etc. except for some classes we ran in the Red Sea. He was much more a cave diver than a wreck diver I liked the BRASSSSSSSSS!!

[Ammers]

The batteries for the master and slave are inside the same housing which means that in a flood you lose all electronics.  Nice. I don't use any agents inside the lid as I don't want to be breathing chemicals  I use a weak windolene mixed with some other cheap anti-bacterials to clean the mouthpiece and the lungs.  

If you like brass then read my thread in Wrecks.  Brass is fun.  The wreck we're diving this weekend has some very stubborn portholes, any tips on getting them off LOL. How about a few kgs of dynamite, blow the f*ckers off.

What do you reckon to alpinism?

[Pete Readey]

Ok!

When we tested our axial flow Prism at DDRC in Plymouth we found that condensation was a big factor because as the hot scrubbed gas from the scrubber came in contact with the lid or surrounding area it got to dew point and condensed even up the inhale hose. This was never a problem on the then semiclosed Prism as we only monitored the O2 in the breathing bag.

The reason to change to a radial flow was extensive, much lower work of breathing, I could use the air gap to condense out most of the water before it got up to the head and then collect the water. We then did some funkyness with the velocity to make sure the sensors stayed dry as much as possible.

If extensive testing is done and you can refine your design it it possible to predict CO2 break through with much greater accuracy. USN data shows this, as did our testing at DCIEM in Canada. This is because dwell time in the canister and gas velocity in the scrubber is longer and slower, plus with insulation we get much greater efficiency over our older design.

The bulk loading issue is of less significance with a radial flow as its more efficient for deeper diving than even going to the Mk15.5/16 design with its huge pancake 11.5 inches across (still axial flow). As an example, USN tests show that the Mk16 canister with 8.5Lbs of 8-12 will give you 300mins to 0.5% co2 SEV

The Prism tested at the same place with 6Lbs 8-12 in similar tests and temps gives the same duration. Please note this is not MY data this is the USN. So my point is CO2 duration is predictable to within a 10-15 minutes or so.

As for passive or active controls, I agree with having both a separate non computer controlled, battery operated secondary backup, that's why we put one on so when the battery goes dead you can stay on the same deco table, however on working dives concentrating on the job you can't rely on manually adding gas or keeping a constant PO2 unless you have your eyes on the passive monitor all the time. (For some this is acceptable)

The electronics don't have to be the weak point if they're sealed away from water, with a low power consumption, with good failure mode analysis and easy to use, plus tested up the ying yang. Many of the problems we have discussed go away if you address the problem, not the symptom.

I haven't dived a CIS Lunar, though I hope to get a dive on Gordon's Kiss someday.

Betadine or Wiskadine works great at keeping the bugs at bay, plus rinse and dry.

Can't comment on Dynamite, though baked beans and a leaky dry suit may help.....:-)

[Ammers]

Haha, good stuff  Unfortunately the design of the scrubber housing on the YBOD means that it can only be one type of scrubber, being able to switch between axial and radial would mean an extensive redesign.  It definitely suffers from the condensation problem but I guess that is perhaps a function of the gas exchanges more than anything.

Do you have an ADV on the Prism?  I don't have one, it's a slob knob for closed circuit, mind you it would help a lot when bombing down a shot line to get some more speed into it.

Take your point on the manual addition of gas thing, it really does change the dive into just getting through it, not getting anything done, I bought a SS bar from a marine shop and have rigged this across the lungs so it's in the middle, the handsets are clipped to it and I can see them without moving my hands. So keeps hands free for other stuff.

Something else - ascent and venting of expanding gas, the common way of thinking in the UK is vent gas around the nose and mouth rather than using the lung pull cord. What I notice is that when dumping around the nose and mouth, the unit seems to keep injecting oxygen at more regular intervals and you can hear the solenoid open for a longer time.  I believe this is because as you come up and dump through the mouth, you dump out fresh O2 before it gets around the loop therefore the box can't get to setpoint.   The downside is if videoing or scootering you have to take a hand off to use the pull cord. I'm trying to think of a way round this.

I got an email from a pleasant chap recently who told me that he confused his new drysuit feed with the O2 bottle and pumped pure O2 in at 50 metres! He was diving on air diluent and immediately started flushing, however as you know the PO2 of air at 50m is quite high and he could not get the O2 reading down quick enough. He had no bailout and had to use his buddy's stages to breathe from while flushing out the loop.  Lots of people publish their mistakes so that the rest of us can learn which is a good thing. How about telling us of any classic blunders you made?  By email if you wish, am23uk@yahoo.co.uk

I find that the change from the high setpoint to the low setpoint takes a long long time to happen if at a constant depth, say you wanted to keep an eye on the CNS clock and dropped your constant PO2 down for a bit, the electronics do not control the drop, only the metabolism of O2 will eventually result in the setpoint dropping at constant depth.  Or dumping gas and adding dil.

A question for you - I don't know if you saw Isler's stuff on redundant rebreathers in the Doux De Coly but it seems evident that this will be the way forward.  I'm going out to France soon and I hope to do Trou Madame right to the end. There's nothing to push there (I'm told!!) but it's a good few kilometres of beatiful passage and I would like to do the full dive.  I am also hoping to video on borrowed equipment. There are a few pure O2 rebreathers on the go and I was considering staging one at 6m to aid deco and get me off the scrubber. I won't be scootering, I could borrow one but that is too much task loading for now.  The swim is a long one and I am concerned about CO2 build up and RMV as the work rate will be high.  If I use the O2 rebreather at 6m I get off the scrubber which will probably be exhausted then.  But bailout is another issue. I am trying to mitigate for a catastrophe happening at the furthest penetration point but that means I need to stage loads of OC bottles along the way!!!

Sorrry...leaving cave mode.....entering wreck mode....do you know that Dave Apperley has organised a trip to Niagara (120m) next year, if you are interested there is 1 space left.

Rgds

[Dominic]

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Originally Posted by [b

Quote[/b] ]A question for you - I don't know if you saw Isler's stuff on redundant rebreathers in the Doux De Coly but it seems evident that this will be the way forward.

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Have you seen Gordon's BOB yet?

[Pete Readey]

Got to be quick.

1. No need to switch. No not gas exchange, gas path design and picking your condensing surface.

2. Yes absolutely there is an ADV! Can't carry a ton of equipment and press buttons on the way down.

3. We use either wrist mount or head down display (always in view.)

4. No pull cords just an automatic dump valve no hands needed or you could dump through your nose as you suggested. We inject at a different point so don't have this issue with oxy being dumped before it's around the system.

5. There is a depth transducer so the unit always knows where it is, set to 1.4 PO2 on the surface, unit defaults to 0.7 PO2 shallower than 18 ft (5 mtrs approx) why fiddle with it? We built a hand set for switchable PO2 but with task loading too many near misses using the wrong set point. The transducer takes the guessing out of the game, means you just concentrate on the job at hand.

6. If the unit is small enough why not take two. O2 rebreathers are good but can only be used very shallow unless you fiddle with them, i.e. mass flow v/v's PO2 monitors etc. then you're back to task loading, or good old open circuit.

7. Yes I think their are two Prisms on that trip as well. It's a wonderful idea to go but I have to concentate on engineering, plus flying a desk is not conjusive with deep dives, not without a couple of months build up.

[Ammers]

Hi Pete. Are you around today?

[Pete Readey]

Yes I am here.

[Mr T.]

John Bantin - you asking after Pete Readey last week? I said I'd dig his details out for you - here they are, along with a highly detailed exhange on various RBs, especially the Prism!

HTH.

PS: Pete's website is listed in his profile

[BJ]

Originally Posted by Mr T.

John Bantin - you asking after Pete Readey last week? I said I'd dig his details out for you - here they are, along with a highly detailed exhange on various RBs, especially the Prism!

HTH.

PS: Pete's website is listed in his profile

There seems to be some confusion. I was not asking after Peter. We are in regular contact. He just sent me a new mouthpiece! ( I did mention he taught me to use a rebreather a long time ago.)
JB