breathing / metabolic simulator

paulraymaekers

hello all,

are tests on rebreathers for CE or other ... done on breathing simulators, or on combined breathing/metabolic simulators..

I was reading on the ANSTI page, they use a breathing simulator where they can inject CO2 at whatever rate they want, this is ok for testing a scrubber, but not for testing PPO2 in a mCCR at different work-levels

that testing is only possible when you 'extract' oxigen from the loop at a certain rate, and injecting CO2 at the same time to test the scrubbers, this means you need a combined breathing/metabolic simulator.

who can explain me how they do it??

regards
paul

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www.rEvo-rebreathers.com

.... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...

abowie

I don't actually know how they do it but the obvious way to my mind would be to not have the Rebreather set up as a loop.

Take out the scrubber and pump gas of the desired mix through it; DON'T recycle the gas after the scrubber, just let it exhaust to air.

THEN pump (a different, premixed) gas of the desired lower PO2 back through the head/whatever you want to test.

I'm sure it's possible to set up some sort of chemical reaction that removes O2 but you run the risk of contaminating the loop with reaction byproducts and affecting your results.

If you want to test an mCCR's O2 decay curve that would of course be more complicated. All I can suggest is injecting a separate gas mix at a known rate into the unit, diluting out the O2 at a pre calculated predictable rate, and see what happens. Obviously you'd end up having to exhaust the equivalent volume of gas from the unit, but it ought to work.

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Andrew Bowie

Rebreather-friendly Buddy

Sten

Hello!

I remember that the Swedish Defence Research Establishment (FOI) had a
student at my university to bulid such a device as a M Sc thisis. This was some fifteen years ago. The base was an existing closed loop breathing simulator that was extedid with a catalytic converter (from a petrol car) and
a system for incjeting Propen (C2H4) into the catalytic converter. Some heat exchangers was allso a part of the system. Both for heating at start and cooling once the combustion was up and running.

In principle this was a device that added heat, CO2 and humidity to the loop while extracting O2. I dont know if the apparatus is in use any more.

Regards!
/Sten

jaap

Hej Sten

I suspect that we are talking about the same guy, AFAIK from talking to him and guys using this test rig a slightly modified version of that setup is still in use.

Ps
My latest D5-modifications worked flawlessly on two boatdives today, very nice!

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My initials: JAAP

paulraymaekers

so if the testing facilities in the UK do not have such a metabolic simulator (that can extract oxigen from the breathing loop), how can they have tested the 2 well know eCCR that have a CE mark, according to 6.6.3 and 6.7 of the named 14143 norm?

(6.6.3 Gas endurance

Test the apparatus with the breathing simulator ventilating at 40 l min

__________________
www.rEvo-rebreathers.com

.... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...

paulraymaekers

__________________
www.rEvo-rebreathers.com

.... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...

paulraymaekers

I try again, as we are looking more detailed into the CE norm..

paul


... fake or not fake, that will be the question.....

__________________
www.rEvo-rebreathers.com

.... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...

iain-hsm

Paul I agree an explanation of the test methods would be useful as there are a number of test requirements to record, but not all the tests need to be done at once. The mechanical nature of the test equipment and number of parameters within each test can be carried out in different phases. Work of breathing (WOB), inhalation/exhalation effort, tidal volume etc are all mechanical with no gas transfer or release required. (Except for volume addition during the compression phase and the reverse for accent) in the case of CC.

The oxygen consumption test is really to record the oxygen injection capabilities and hysteresis of the gas sensor, the gas control accuracy and solenoid control dead band limits, when compared to depth, time, humidity etc, and the accuracy for it (the system) to monitor measure and replenish from a mechanical simulation of either a fixed or variable metabolic consumption.

The simplest mechanical method is volume extraction by calibrated flow meter from the oxygen rich side. There is no metabolic oxygen onversion/extraction devise. To mimic metabolic consumption a calibrated flow is removed from the breathing loop with this volume loss being made up (partially) by the C02 addition, performed by either mass flow transducer, or again by flow meter (Depending on the operational depth) The C02 rich addition is also part of the canister duration test.

To achieve flow there has to be a pressure drop so the flow meter (over bottom depth) has to be precise as to partial pressure and bottom pressure (depth). Other methods to consider are calibrated (Span) gas, where a C02 rich gas mixture can be used to load the C02 canister under test with the analysis down stream of the canister to test for a C02 spike breakthrough against a known or increasing flow or BPM or tidal volume. Both techniques are valid and allow the unit under test to be tested to failure. Span gas has the advantage of including other trace mixtures. Iain Middlebrook.

Duncan Price

Err, not to highjack the thread, but thanks for sending the rocket tube. Any luck with the video?

jptaylor9

You mean something like this???

Ambient Pressure Diving Ltd. R&D