Count the Counter lungs

A friend just asked an interesting question:  Why have two counter lungs vs one?

I must admit, that no one ever told me an answer to this question, but here is my reasoning for 2 vs 1:
One counter lung only lets the scrubber work during half of the breathing cycle.
If the lung is on the exhale side, then it inflates on exhale, but gas only passes through the scrubber on inhale.
If it’s on the inhale side, then gas passes through the scrubber only on the exhale.

If you have two counter lungs, half the gas passes through the scrubber as you exhale, and half passes through as you inhale. This makes the gas pass through the scrubber slower, (aka dwell time)  and therefore the scrubber is more effective.  I would also assume that the slower gas movement would decrease the work of breathing of the unit.

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