Minimum loop. Simplifying & personal methods.

[Tech Alex]

a while ago I was asked by a friend quite new to ccr what’s the best way of maintaining minimum loop,
I found myself describing how I do so (on a Borris) but then had to explain that my method wouldn’t work on their machine, I admit, I shut the slider for the O2 once I reach bottom and then just fly manual from there on. On another ccr I have, I have to “search for minimum loop” (exhale part of my breath every time I feel the unit inject) about every 4th breath or so,
Which lead me in to thinking is there a set pattern or trick people use on their units? Granted every unit operates slightly differently but I’m interested to hear other people’s tricks and knacks. Call it having an open mind.

 

[DeepUnderground]

Correct weighting plays the biggest part, if your correctly weighted then you begin to rise if you have much over minimum loop volume

 

[Bobjr]

a while ago I was asked by a friend quite new to ccr what’s the best way of maintaining minimum loop,
I found myself describing how I do so (on a Borris) but then had to explain that my method wouldn’t work on their machine, I admit, I shut the slider for the O2 once I reach bottom and then just fly manual from there on. On another ccr I have, I have to “search for minimum loop” (exhale part of my breath every time I feel the unit inject) about every 4th breath or so,
Which lead me in to thinking is there a set pattern or trick people use on their units? Granted every unit operates slightly differently but I’m interested to hear other people’s tricks and knacks. Call it having an open mind.

Why would you shut off O2 - that seems like hypoxia waiting to happen. Also if your unit injects it is because you have changed loop volume (either increase in depth resulting in dil being added) or you have metabolised O2 from loop. For the latter if you vent you are reducing loop volume which means you can't have been at minimum loop volume in first place and are now negatively buoyant.

 

[JonG]

I think it depends on overall loop volume and how closely matched it is to your lung volume, my unit is very close and I tend to find that if I try and reduce the volume by much, WOB worsens even before the ADV triggers and I start getting a negative pressure situation in my mask which is really disconcerting and soon focuses the mind.

 

[Tech Alex]

Why would you shut off O2 - that seems like hypoxia waiting to happen. Also if your unit injects it is because you have changed loop volume (either increase in depth resulting in dil being added) or you have metabolised O2 from loop. For the latter if you vent you are reducing loop volume which means you can't have been at minimum loop volume in first place and are now negatively buoyant.

You are correct in what you say, but on longer dives it makes a huge difference to gas consumption, effectively with this unit all you’ve done is make it an mccr rather than an eccr, it’s how something like a kiss classic is anyway, I find it very natural to vent and inject in a sort of pattern, I know of guys that run them manually 100% of the time, they’re a good unit, and it does work with them, although you have to be familiar with it and dive it often,
Your question is pertinent and this is what I want to know with other people’s units,

 

[Tech Alex]

I think it depends on overall loop volume and how closely matched it is to your lung volume, my unit is very close and I tend to find that if I try and reduce the volume by much, WOB worsens even before the ADV triggers and I start getting a negative pressure situation in my mask which is really disconcerting and soon focuses the mind.

Yes I remember this affair on another unit I have while I got truly ofay with it,

 

[rjack]

On my kiss where I commonly use a 'hot' dil because i am diving in caves and its all offboard and my BO as well - I just exhale through my nose until the adv fires. If I am on the bottom that ends up resetting me at ppo2 1.0-1.2 anyway and there's very little O2 to add.

On my meg in open water I do the same but because my dil is usually much lower fO2 I typically have to make up some for the adv firing and add O2 to bring the ppO2 back up. Once I have brought the O2 back up I usually vent about half a breath via my nose then shut the adv. The unit will stay at min loop with just the solenoid making up for the metabolized volume until ascent. On ascent I will overvent via the dump or my nose then makeup for the lost volume with O2 (I need it anyway to compensate for drop on the ascent)