The misunderstood mCCR explained

[Jeremy Williams]

I asked that very question when I was getting into CCR, and was dissuaded. It seemed like the best of both worlds: eCCR as a parachute, and needle valve to minimize MAV pushes. But I was told that I would no longer hear the background click of the solenoid in e mode or as a reminder if flying manually when I got task saturated. And absent that background noise, if my seldom used solenoid failed, I wouldn't be reminded by the silence and would be at greater risk of missed hypoxic change.
Your thoughts?

I believe that your pre-breathe should include exercising the solenoid and validating that it is functioning correctly. Arguably, that's the ONLY point of the pre-breathe. At that point, you have two scenarios...

1. The unit is flying itself to set point. You become severely task loaded and unaware of your ppO2. Your only method of maintaining your ppO2 is your unit set point. There are half a dozen ways that the unit can fail and become hypoxic at this point, including running out of O2, or a solenoid failure, or a battery failure just to name a few. You hope that the subconscious awareness of those clicks (none is bad, too many is also bad) will remind you to become aware of your ppO2 again.

2. You are flying the unit manually using the MAV. You become severely task loaded and unaware of your ppO2. Your primary method of maintaining your target ppO2 has failed (your brain). Your unit's set point is your backup method and is now active. There are still the same number of ways that the unit can fail and become hypoxic. You hope that hearing the solenoid fire at all will remind you that you haven't been flying your unit manually, that your target ppO2 has now dropped to your set point, and that this reminder will make you become aware of your ppO2 again. You also hope that the muscle memory of firing the MAV will remind you to become aware of your ppO2 again.

Of those two scenarios, I like #2 better. Just my opinion. I don't see greater risk there. When I hear that solenoid click it's like somebody has kicked me in the ass. My controller is in front of my face ASAP.

 

[rjack321]

I asked that very question when I was getting into CCR, and was dissuaded. It seemed like the best of both worlds: eCCR as a parachute, and needle valve to minimize MAV pushes. But I was told that I would no longer hear the background click of the solenoid in e mode or as a reminder if flying manually when I got task saturated. And absent that background noise, if my seldom used solenoid failed, I wouldn't be reminded by the silence and would be at greater risk of missed hypoxic change.
Your thoughts?

The revo people love hybrids because the eCCR version eats batteries. The rest of us, having a solenoid parachute is not really relevant. If you are so task loaded that you lose track of your ppO2 you shouldn't be diving CCR period. You need to always know your ppO2 first. Pushing the MAV every 10 minutes (or more) is something you just do because its part of the dive and you know your ppO2 so you know when you want more in there. You are not looking at your watch trying to gauge when 10mins is or isn't up.

About the only time the solenoid in a hybrid would be useful is on the surface to keep the loop from going hypoxic. If your ADV fires hypoxic dil on the surface a CMF is not going to keep the loop breathable. At least on the Revo (the most common unit dove as a hybrid) the ADV is so bad that it never fires so the solenoid in the hybrid is kind of useless.

CMFs can clog and solenoids can stick open, closed, or run out of battery so having both can cause just as many, yet different, problems than they solve. Having an ADV shutoff is the solution to the surface firing, in addition to never putting dil in the loop on the surface/shallow. At depth I have never wished my Kiss mCCR had a solenoid (and not really on the surface either but I could see the rationale). And I have never wished my Meg eCCR had an orifice either. Batteries in the Meg last 25-30 hours even in frigid waters and checking the battery is part of the build checklist.

 

[Dsix36]

I asked that very question when I was getting into CCR, and was dissuaded. It seemed like the best of both worlds: eCCR as a parachute, and needle valve to minimize MAV pushes. But I was told that I would no longer hear the background click of the solenoid in e mode or as a reminder if flying manually when I got task saturated. And absent that background noise, if my seldom used solenoid failed, I wouldn't be reminded by the silence and would be at greater risk of missed hypoxic change.
Your thoughts?

My thought is that if I ever do actually hear the solenoid fire, it means I really fooked up and should be dead. I keep my setpoint very low ( as in .4) as one last great hail Mary. Nothing is fool proof but as long as I check the solenoid function during the build and prior to the dive, I have limited faith in in ( the same as any other solenoid setup for me). the same old logic is this - Always know your po2.

I have used probably every imaginable setup and the only one that really concerns me is fully manual as it requires much more frequent attention than any others. Even that is manageable if you have the right mindset and dicipline. my bailout rebreather is this way intentionally as there is less electronics to fail, and bailout needs to be as reliable as possible.

Wearing a thick hood blocks the sound of the solenoid for me most times anyway so it really is a moot point.

 

[broncobowsher]

The rEvo doesn't have a solenoid to fire Dil. Only solenoid is O2.
Dil is ADV or manual add only. I know people who hate the rEvo ADV so much they disable it leaving them only the manual add.

 

[rjack321]

The rEvo doesn't have a solenoid to fire Dil. Only solenoid is O2.
Dil is ADV or manual add only. I know people who hate the rEvo ADV so much they disable it leaving them only the manual add.

Not seeing where I implied that there was a dil solenoid? But perhaps I'm not seeing my own writing the same way

 

[rjack321]

2. You are flying the unit manually using the MAV. You become severely task loaded and unaware of your ppO2. Your primary method of maintaining your target ppO2 has failed (your brain). Your unit's set point is your backup method and is now active. There are still the same number of ways that the unit can fail and become hypoxic. You hope that hearing the solenoid fire at all will remind you that you haven't been flying your unit manually, that your target ppO2 has now dropped to your set point, and that this reminder will make you become aware of your ppO2 again. You also hope that the muscle memory of firing the MAV will remind you to become aware of your ppO2 again.

Of those two scenarios, I like #2 better. Just my opinion. I don't see greater risk there. When I hear that solenoid click it's like somebody has kicked me in the ass. My controller is in front of my face ASAP.

What's your setpoint and what seems to be the instigator for the solenoid firing? Is this happening on a busy ascent?

 

[HKGuns]

This layperson newbie didn't get confused until he read the thread after reading the article. I thought the article was very well written and made an unfamiliar subject easy to understand.

 

[jale]

As mentioned by Rjack and others, I don't get the "task loaded" reference.
Diving RB, the only task is monitoring your po2. Everything else should be done without being a "load".
The only time, you don't get to check your po2 is when you bail out.
I personally only dive mccr with a needle valve, or a cmf.
I also have dived, and sometime still dive, a completely pure manual with.only a mav to inject o2 when you need. Dangerous? For me no as you know you MUST check the monitor. And I believe it is a good way to learn RB as it makes you fully aware of the decrease of the po2, the relation between o2 metabolism and change of buoyancy (at constant depth of course), increase and decrease of o2 consumption and.so on...but this is another topic

 

[fsardone]

As mentioned by Rjack and others, I don't get the "task loaded" reference.
Diving RB, the only task is monitoring your po2. Everything else should be done without being a "load".
The only time, you don't get to check your po2 is when you bail out.
I personally only dive mccr with a needle valve, or a cmf.
I also have dived, and sometime still dive, a completely pure manual with.only a mav to inject o2 when you need. Dangerous? For me no as you know you MUST check the monitor. And I believe it is a good way to learn RB as it makes you fully aware of the decrease of the po2, the relation between o2 metabolism and change of buoyancy (at constant depth of course), increase and decrease of o2 consumption and.so on...but this is another topic

Agreed,
that is why every few dives, I do one in which I select setpoint LOW .7 and then fly the machine at the usual 1.3 for a shallow 1.5 hours (shallow 30-40 mt).

It gives you the sense of what to expect when going manual.

 

[Jeremy Williams]

What's your setpoint and what seems to be the instigator for the solenoid firing? Is this happening on a busy ascent?

Setpoint was 1.0 and I was flying the unit to 1.25 or so... and most recently the instigator seemed to be a bottle on the wreck of the Hebe that I was reaching shoulder deep into the wreckage to retrieve. It didn’t want to be retrieved for some reason and tied up both of my hands for a bit longer than I realized.