1 Counter lung vs 2?

[lostsheep]

RB80 and SF2 both use single bellows counterlung.

I can only speak for the SF2 but the one potential downside is counterlung volume.

Due to the position of the counterlung the SF2 dewaters VERY easily. Work of breathing is very position dependent

Sounds like it's the position of the CL on the SF2, not the number of CLs.

You planning to build one?
Oxydiver has very interesting ones on his site.

Please don't put bad ideas in my head, I have enough already

 

[Gone for diving]

This looks like one to me. Kiss Spirit.
View attachment 720830

This system the scrubber is part of the hose... so it will not slow down, only if you breath slower. But scrubs twice

 

[PfcAJ]

RB80 and SF2 both use single bellows counterlung.

I can only speak for the SF2 but the one potential downside is counterlung volume.

Due to the position of the counterlung the SF2 dewaters VERY easily. Work of breathing is very position dependent

The limited volume on the RB80 helps with heavy breathing situations. You end up venting more exhaled gas and reducing co2 burden on the scrubber since the cournerlung is pre-scrubber.

 

[tbone1004]

KISS Sidekick, Spirit, and Sidewinder all use single counterlung, as do the RB80 and it's offspring like the SF2.

In terms of breathing, it is much more about the location of the lung/s than it is about the quantity of the lungs. In a backmounted rebreather a single lung would be unbalanced and would adversely affect breathing, but in something like the units mentioned above it wouldn't really matter if they split them.

 

[FIGJAM007]

Split counterlungs are used when there are two counterlungs, one for the inhaled gas and one for the exhaled gas. They are flexible bags and must have enough volume to contain a full inhalation or exhalation. They can be mounted on the front, back or over the shoulders of the diver, their position affects the breathing resistance at various attitudes. A front mounted counterlungs makes inhalation easier than exhalation in a normally swimming diver. With a back mounted counterlungs exhalation is easier due to hydrostatic pressure. The ideal position for a counter lung is when it is balanced to the centroid, this point is about 19 cm below and 7 cm behind the sternal-notch in the upright position, in the average person. With twin shoulder mounted counter lungs there are several advantages. On inhalation the upstream counter lung collapses and causes gas to move from the downstream counter lung due to hydrostatic pressure. This helps the gas move through the CO2 adsorbent making the work of breathing less. Conversely on exhalation the downstream counter lung inflates, this causes a pressure differential with the inhale counter lung which draws the gas through the breathing loop ready for the next inhalation. Slit counterlungs are not always "over the shoulders". The dolphin has split counterlungs but not over the shoulder. Copied from another website but a great explanation of why it’s used. Backmount lungs fail CE in head down position usually and get a exemption of sorts. I think the kiss units are undergoing CE so will be interesting to see how they go.​

 

[1c3d1v3r]

Sentinel is another singe counter lung model.
Dual counter lungs half the peak flow rate.

If using one counter lung only then front mount units use exhale counter lung and backmount units use inhale counter lung.

A backmount unit got a thermal advantage with a single counter lung. The exhaled gas goes straight to the scrubber and doesn't cool down in an exhale counter lung. I don't know however if the advantage is worth the higher peak flow rate.

 

[Akimbo]

Exhalation counterlungs are useful for water separation. A lot of mine-safety pure Oxygen rebreathers were modified for underwater use in the 1950s. Many of them used a single hose, which meant exhaling and inhaling through the absorbent canister inside the bag.

Toxic cocktails reduced significantly once they figured out that this was a flawed concept underwater.

 

[tbone1004]

​ Split counterlungs are used when there are two counterlungs, one for the inhaled gas and one for the exhaled gas. They are flexible bags and must have enough volume to contain a full inhalation or exhalation. They can be mounted on the front, back or over the shoulders of the diver, their position affects the breathing resistance at various attitudes. A front mounted counterlungs makes inhalation easier than exhalation in a normally swimming diver. With a back mounted counterlungs exhalation is easier due to hydrostatic pressure. The ideal position for a counter lung is when it is balanced to the centroid, this point is about 19 cm below and 7 cm behind the sternal-notch in the upright position, in the average person. With twin shoulder mounted counter lungs there are several advantages. On inhalation the upstream counter lung collapses and causes gas to move from the downstream counter lung due to hydrostatic pressure. This helps the gas move through the CO2 adsorbent making the work of breathing less. Conversely on exhalation the downstream counter lung inflates, this causes a pressure differential with the inhale counter lung which draws the gas through the breathing loop ready for the next inhalation. Slit counterlungs are not always "over the shoulders". The dolphin has split counterlungs but not over the shoulder. Copied from another website but a great explanation of why it’s used. Backmount lungs fail CE in head down position usually and get a exemption of sorts. I think the kiss units are undergoing CE so will be interesting to see how they go.​

That quote is a bit misleading. When you have a dual lung design you do have one lung on the exhale side and one on the inhale side in that you are breathing directly into one and directly out of the other, but you are doing that simultaneously not sequentially. When you exhale, you are exhaling into the counterlung and then due to hydrostatic pressure the lungs are going to be balanced so the gas is flowing through the scrubber and into the inhale lung. When you start inhaling you pull the gas directly out of the inhale lung and then pull the gas from the exhale lung through the scrubber and directly into your lungs. This is ideal compared to a single lung because it moves half the gas through the scrubber on inhale and half on exhale, but for normal use it's not going to make any difference to the diver.

 

[lostsheep]

The idea that different pressures in the lungs would help drive the gas around the loop and thus lower WOB would seem to violate the law of conservation of energy; work is done and nothing is free.

Based off of the lack of consensus here it sounds like there isn’t a simple answer to 1 vs 2.

 

[Gone for diving]

The idea that different pressures in the lungs would help drive the gas around the loop and thus lower WOB would seem to violate the law of conservation of energy; work is done and nothing is free.

Nothing is free,
if the counter lung is above your lungs you have free exhale, Work for inhale
and vice versa, with front mount,
On a back mount twin counter lung,
If you roll one way for exhale and there was a checkvalve, between the counter lungs then roll the other way and back, you could pump the air through...
But that's to much work!

I am surprised that no one has make a fan assisted rebreather of some sort...