Hi everyone,
I have been doing some researching on rebreather systems and came across a piece of knowledge that I would like some input on. The video in question is a Youtube video published by InnerSpace Systems for the assembly of their Meg15 CCR:
This question was also cross-posted in the comments by myself.
In the video (checklist step 26 at around the 4:40 mark) the manufacturer suggests only opening the valves to both tanks 1.5 turns. He claims to do this based on the idea that if they are only open that much you could save gas loss during a catastrophic "boom" scenario.
The meat of my question is whether or not this is true, and if so can it be applied to Open Circuit diving as well?
To an uninformed layman (myself) it used to seem that valves felt more or less to be an on-off switch. There was that 5 degree knob turn between no air and "OMG ALL THE AIR!" then there is the 5 more turns of "why did they add this many turns on the knob" to open the valve to the stopping point (full open) then back it off a quarter of a turn. Once I began diving deeper I was informed that the valves were not simply on/off but indeed a gradient and that not opening them all the way could cause WOB to increase at depth due to the lag time created by air passing through a marginally open valve. In addition, I was told that full open is better and reduces the risk of the knob being bumped or rubbed accidentally into the off position.
To extrapolate on my first question, is the "1.5 turn open" standard practice across all CCR units? And is it widely believed to be an effective stoploss method as stated in the video? I understand that on CCR the amount of gas being provided does not need to match the flow rate of OC and therefore the 1.5 turn method would be acceptable. To me the logic seems to hold up.
To revisit the second question about it being applied to Open Circuit, why wouldn't this method be taught the same to new divers in entry level certification courses? The benefit during a catastrophic free flow seems like it would translate to any type of diving. Sure there is the potential WOB issue, but I wouldn't think an entry level diver is going deep enough for it to be a problem. It may well also be that it has been deemed safer to have new divers error on the side of caution with a more or less fully open valve versus one that is closer to being closed.
My final question is if CCR divers practice the 1.5 turn open and then bails out (assuming the BOV or emergency second stage was connected to the CCRs diluant tank first stage) does he/she then open the diluant tank valve to the "standard" full open position to breathe as would be the standard position for OC?
Thanks in advance. I really hope I didn't make an incorrect assumption or miss something obvious.
I have been doing some researching on rebreather systems and came across a piece of knowledge that I would like some input on. The video in question is a Youtube video published by InnerSpace Systems for the assembly of their Meg15 CCR:
This question was also cross-posted in the comments by myself.
In the video (checklist step 26 at around the 4:40 mark) the manufacturer suggests only opening the valves to both tanks 1.5 turns. He claims to do this based on the idea that if they are only open that much you could save gas loss during a catastrophic "boom" scenario.
The meat of my question is whether or not this is true, and if so can it be applied to Open Circuit diving as well?
To an uninformed layman (myself) it used to seem that valves felt more or less to be an on-off switch. There was that 5 degree knob turn between no air and "OMG ALL THE AIR!" then there is the 5 more turns of "why did they add this many turns on the knob" to open the valve to the stopping point (full open) then back it off a quarter of a turn. Once I began diving deeper I was informed that the valves were not simply on/off but indeed a gradient and that not opening them all the way could cause WOB to increase at depth due to the lag time created by air passing through a marginally open valve. In addition, I was told that full open is better and reduces the risk of the knob being bumped or rubbed accidentally into the off position.
To extrapolate on my first question, is the "1.5 turn open" standard practice across all CCR units? And is it widely believed to be an effective stoploss method as stated in the video? I understand that on CCR the amount of gas being provided does not need to match the flow rate of OC and therefore the 1.5 turn method would be acceptable. To me the logic seems to hold up.
To revisit the second question about it being applied to Open Circuit, why wouldn't this method be taught the same to new divers in entry level certification courses? The benefit during a catastrophic free flow seems like it would translate to any type of diving. Sure there is the potential WOB issue, but I wouldn't think an entry level diver is going deep enough for it to be a problem. It may well also be that it has been deemed safer to have new divers error on the side of caution with a more or less fully open valve versus one that is closer to being closed.
My final question is if CCR divers practice the 1.5 turn open and then bails out (assuming the BOV or emergency second stage was connected to the CCRs diluant tank first stage) does he/she then open the diluant tank valve to the "standard" full open position to breathe as would be the standard position for OC?
Thanks in advance. I really hope I didn't make an incorrect assumption or miss something obvious.