Open Circuit, Closed Circuit

[fjpatrum]

Okay, I'm new. I've been reading a lot here, but I can't figure out exactly what is meant by open circuit and closed circuit. I know closed is what people call re-breather dives, or at least I think I know that, but I don't understand where the terminology comes from.

Closed circuit implies, to me, a continuous loop, which makes sense with a re-breather having a scrubber. Open circuit would then be the fact that there isn't a continuous loop but how did the terminology come about? A bunch of EE geeks who were also divers just start cross-pollenating jargon or what?

 

[tstormdiver]

Open circuit is like the type of scuba typically used by divers, the exhaust is vented straight into the open water. Once exhaled, it is gone. Closed circuit is like you said a loop (as in a rebreather) where the exhaust is recirculated through a scrubber to remove the waste CO2, the air is rebreathed & typically there are no bubbles.

 

[Cave Diver]

Open circuit would then be the fact that there isn't a continuous loop but how did the terminology come about? A bunch of EE geeks who were also divers just start cross-pollenating jargon or what?

As far as I can tell, the terminology was applied to the first Aqua-Lungs made by Jacques Cousteau to differentiate the way they worked from the rebreather systems the Navy had been using for years.

 

[Walter]

I usually cover this concept on the first night of class. Do others not teach it anymore?

 

[Cave Diver]

I usually cover this concept on the first night of class. Do others not teach it anymore?

As I understand his question, he seems to understand the concept, he's just asking this history of the terminology. i.e. how/when where the terms OC and CC coined as they relate to SCUBA.

 

[Walter]

Reading his post, it's a little more than that.

I can't figure out exactly what is meant by open circuit and closed circuit. I know closed is what people call re-breather dives, or at least I think I know that

Either way, the concept of why they are called closed, semi-closed, and open circuit is (I thought) covered in the introduction to SCUBA along with what SCUBA means.

 

[Cave Diver]

This was the basis for my comment. He appears to understand the comment, but asks about the origins.

Closed circuit implies, to me, a continuous loop, which makes sense with a re-breather having a scrubber. Open circuit would then be the fact that there isn't a continuous loop but how did the terminology come about? A bunch of EE geeks who were also divers just start cross-pollenating jargon or what?

 

[Walter]

I saw that as part of the question.

 

[fjpatrum]

Walter, there was absolutely nothing about rebreathers or the history of SCUBA taught in my OW course. And there was definitely no discussion about open circuit, closed circuit or semi-closed (which I haven't heard of until your post above). In fact about the only history of scuba covered was asking whether everyone knew what SCUBA actually means. Only 2 of us in my class knew that.

When I started the post, I was a bit confused but by the time I finished I think I had a good idea about the actual differences just from thinking it through. That's why I started asking about the history of it as well, since it's not exactly intuitive to me to call it "open circuit" or "closed circuit" unless someone is familiar with electronics in general.

Thanks, everyone, for your help and comments.

 

[g1138]

In the early days they didn't have modern first stage set-ups
You had a round "first stage" about the size of a small dinner plate and two hoses going into/out of it.
This was essentially a semi-closed circuit regulator.
Air would be breathed and then sent back to the first stage which would eventually release excess air. I don't remember if there was any major scrubbing going on.

Eventually the first single hose regulator (AKA open circuit) was made and this is where the distinction came from.

As for where the terminology came from, I don't know the exact history timeline for it.