O2 cells before or after the scrubber?

Mdemon

Here's the scrubber:



And here's a likely place for the cells:



I'm thinking of adding PO2 control to an FGT co-axial scrubber. However, the easiest place to put the cells is before the scrubber. I'm wondering how much the CO2 will affect the readings and final PO2 once scrubbed... Any mathematicians out there please?

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"Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"

Marc T

IMHO the CO2 dont affect the reading, the ppo2 is a little bit lower of course
thats what you have on a Ray scrubber when using the pport at the bottom of the scrubber.
Make me think that what I have done on a backup Rebreather using a Ray scrubber was to invert the flow, so the sensors are in the standard position, perhaps you could do the same thing, yes you loose the water trap but its probably better than having the sensor in the water trap.

Mdemon

Yes, I was trying to find out roughly how much lower - my Maths isn't that good.

The scrubber is mounted horizontally. You raise a good point about water - I'll have to add some absorbent just in case. I could switch the gas flow too, I am still thinking what this could do to the scrubber efficiency though.

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"Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"

ReikiMaster

i would have thought that the main problem would be from a lack of mixing of the o2 added, ie spikes on the sensors, whereas if the gas has passed through the scrubber there will be a more consistant reading.

Mdemon

I was planning to put a solenoid in the same place as the cells. Works OK on the Inspo?

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"Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"

Marc T

So very rough thought

What you certainly dont have to enter in the computations is ambient pressure due to the definition of partial pressure.

Few computations ( considering one vol of O2 become a vol of co2, show that at ambient pressure, the difference of ppo2 is the same whatever the inhale ppo2 is ).

The difference of ppo2 between inhale and exhale is always the same, whatever the exercice and consumption of O2 are, only the flow is increased.

So I guess the difference of ppo2 between inhale and exhale is always the same whatever the conditions are.

So what you have to do is to calibrate and then exhale only one time in the scrubber so the difference between 0.21 and the displayed value will be the difference youll always have between inhaled and exhaled gaz.

BUT AFTER the scrubber its an other storry because CO2 have been scrubbed, then the PPO2 increase BEFORE any O2 addiction.

So if your sensor is before scrubber, you can think that the solenoîd will give you a more O2 than if it was after and the difference will increase with the quantity of scrubbed O2...so perhaps not a good idea.

Hum dont know if what I wrote worth 2 pences

Cheers

Marc

Beanie

I'm going to put in for 0.03

Although I can't see it making a huge difference.

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RAL

Thats what I would think. Plus isn't CO2 hard on the cells?

RAL

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Mdemon

I hadn't heard about CO2 being hard on cells. Got a link?

Beanie, you have to show your working! How did you get 0.03?

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"Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"

Marc T

Hum yes difference between really inhaled gaz and exhaled will be 0.03 in any case, CO2 scrubbing will increase but the flow rate too so diffrence of PPO2 between every part of the loop will stay constant.