Recommended options on new rebreather (Optima CM)

[lostsheep]

I'm all about convenience of things to stay on the loop when stuff breaks, don't get me wrong. That said there are about 6 O2ptima CM divers that will ever be in a situation where you are going to actually really want to stay on the loop for the rest of the dive. Dive a hot dil, if the electronics work in SCR mode then you aren't using hardly any O2 anyway while you're at the bottom. If this is for an OW dive, leave the shutoff off and just bailout, it's good practice anyway.

I’m primarily an open water diver.
I took the o2 shutoff off of my CM.
I’m staying on the loop if I can.

So make that “about 7” of us.

 

[mdwalter]

If you don’t have the inline valve, you indeed need to close the tank valve and feather which I find less convenient.

Not really. You can disconnect the LP hose from the Y block the O2 MAV, then disconnect the LP hose from the O2 bottle to the Y block and plug it directly into the O2 MAV. Don't forget to also loop back the LP hose on the Y block back to the now open LP nipple on the Y block, especially if the solenoid is stuck open or repeatedly firing, to prevent water from getting into the head. This will allow you to leave the O2 turned on and fly manually with the O2 MAV. Yes, it's a PitA, but it will work in the unlikely event you have a stuck solenoid.

 

[Heat Miser]

I'm all about convenience of things to stay on the loop when stuff breaks, don't get me wrong. That said there are about 6 O2ptima CM divers that will ever be in a situation where you are going to actually really want to stay on the loop for the rest of the dive. Dive a hot dil, if the electronics work in SCR mode then you aren't using hardly any O2 anyway while you're at the bottom. If this is for an OW dive, leave the shutoff off and just bailout, it's good practice anyway.

@tbone1004 forgive my ignorance but what is a hot dil. You mean O2 enriched dil so something greater that 21%, i.e. something typically suitable for SCR mode (depth dependent)?

If your running in SCR mode, its easier to close the in-line shut off to ADV, unclip the dil low pressure inflator, close of the O2 in-line shut off, diconnect and plumb the dil into the O2 Inflator Valve. So not having the in-ine shut off on O2 I would argue you can never run in SCR mode. You can continue to run the dil through the ADV, but its not a great manual add button for this purpose, I practiced both ways and the latter sucks.

The other thing that is useful is in-water doffing. For those with a bit of girth (36 inch waist, I can still see my toes) it can be a pain to get up a ladder to a boat with the chop in the front. Click off the in-line shuts offs, detach and hand it up like a stage. I would assume scrounging over sumps or leaving the unit staged you need the inline shut-off (assuming your carrying your O2 ass mounted)

 

[tbone1004]

@tbone1004 forgive my ignorance but what is a hot dil. You mean O2 enriched dil so something greater that 21%, i.e. something typically suitable for SCR mode (depth dependent)?

If your running in SCR mode, its easier to close the in-line shut off to ADV, unclip the dil low pressure inflator, close of the O2 in-line shut off, diconnect and plumb the dil into the O2 Inflator Valve. So not having the in-ine shut off on O2 I would argue you can never run in SCR mode. You can continue to run the dil through the ADV, but its not a great manual add button for this purpose, I practiced both ways and the latter sucks.

The other thing that is useful is in-water doffing. For those with a bit of girth (36 inch waist, I can still see my toes) it can be a pain to get up a ladder to a boat with the chop in the front. Click off the in-line shuts offs, detach and hand it up like a stage. I would assume scrounging over sumps or leaving the unit staged you need the inline shut-off (assuming your carrying your O2 ass mounted)

hot dil=a high ppO2 at the bottom. I personally use the same gas for dil as I would if diving on OC following standard gases. Some will use one gas deeper, but that still has your ppO2 around 1.0 instead of 1.3 at MOD.

I have a dil MAV, I would not disconnect the ADV to get access to the O2 MAV but running in SCR mode isn't bad if you have a functioning ADV since you can breathe against it to inflate or press the button. It isn't as precise as pressing a MAV button, but it's running in SCR mode isn't exactly about ultimate precision. I also use different QD's for Dil and O2 since the Dil side needs to run a BOV and is a QC6 for me with the O2 being a BC Inflator. I have an adapter, but that's emergency use only.

No excuse for in-line shutoff on an O2ptima CM though IMO, the valve is literally right there so there and since it is an eCCR without any sort of constant O2 flow there are very few instances where you should ever have to turn the O2 off. Flip it to low ppO2 or as low as you can set it and the solenoid shouldn't fire.

 

[Heat Miser]

I have a dil MAV, I would not disconnect the ADV to get access to the O2 MAV but running in SCR mode isn't bad if you have a functioning ADV since you can breathe against it to inflate or press the button. It isn't as precise as pressing a MAV button, but it's running in SCR mode isn't exactly about ultimate precision. I also use different QD's for Dil and O2 since the Dil side needs to run a BOV and is a QC6 for me with the O2 being a

@tbone1004 so you don’t have the ADV you have the higher pressure MAV (without the ADV)? I have been told that better for adding dil rapidly. But I’m a fiscal tight ass.

The one thing I would say about running dil through the O2 manual add when in SCR mode is because it’s being added through the exhal lung, the sensors are picking up a more accurate PP02 that you are breathing. When you run SCR mode through the ADV manual add (which is a pain in the ass) the po02 is noticeably lower because it been breathed and expelled once.

 

[tbone1004]

@tbone1004 so you don’t have the ADV you have the higher pressure MAV (without the ADV)? I have been told that better for adding dil rapidly. But I’m a fiscal tight ass.

The one thing I would say about running dil through the O2 manual add when in SCR mode is because it’s being added through the exhal lung, the sensors are picking up a more accurate PP02 that you are breathing. When you run SCR mode through the ADV manual add (which is a pain in the ass) the po02 is noticeably lower because it been breathed and expelled once.

The ADV should add dil quite quickly, on my sidemount unit I use the ADV as my dil MAV. No need to add an extra MAV on the CM since you have easy access to manually press the ADV for dil addition. The comment about precision is just about the type of valve that is used but it's not like the O2 side where you need ultra precision addition.

 

[LFMarm]

Many thanks to all of those (incl. @tbone1004 and @mdwalter) that shared their experience in this thread. I dived about 70h with the configuration I described in a post here but came to the conclusion that 2 of the suggestions that I did not follow were actually right:

1) QC6 on an Optima CM without BOV doesn't make sense unless you do it to have same configuration to your diving buddies on QC6. The amount of diluent needed is never high enough to require a higher flow connection than the regular inflator hose one. When you go deeper, your gas density also goes down with the result that you never actually need a QC6. I did get the QC6 on my Optima and I am now using it but always carry a cheater adapter to be able to plug off board bottles from divers that are not on QC6. Only minor advantage of QC6 in. my setup is that I can offboard both QC6 and regular inflator hose. It definitely is not worth the hundred of dollars required to upgrade the connections and get the cheater.

2) The O2 shutoff after the Y-valve is not a good idea. As per the post below, I just removed the O2 shutoff valve and implemented this procedure in case of solenoid failing open.

Not really. You can disconnect the LP hose from the Y block the O2 MAV, then disconnect the LP hose from the O2 bottle to the Y block and plug it directly into the O2 MAV. Don't forget to also loop back the LP hose on the Y block back to the now open LP nipple on the Y block, especially if the solenoid is stuck open or repeatedly firing, to prevent water from getting into the head. This will allow you to leave the O2 turned on and fly manually with the O2 MAV. Yes, it's a PitA, but it will work in the unlikely event you have a stuck solenoid.

I also replaced the O2 hose from the regulator with the new version that has a screw to lock the inflator hose attachment instead of the small plastic spacer. Now there are no finicky plastic spacers anymore on the O2 line (there were 2 on the unit that I started diving on).

I feel this setup is less prone to mistakenly shutting off O2.

 

[Tracy]

1) QC6 on an Optima doesn't make sense unless you do it to have same configuration to your diving buddies on QC6. The amount of diluent needed is never high enough to require a higher flow connection than the regular inflator hose one. When you go deeper, your gas density also goes down with the result that you never actually need a QC6. I did get the QC6 on my Optima and I am now using it but always carry a cheater adapter to be able to plug off board bottles from divers that are not on QC6. Only minor advantage of QC6 in. my setup is that I can offboard both QC6 and regular inflator hose. It definitely is not worth the hundred of dollars required to upgrade the connections and get the cheater.

If you change that to say Optima CM then I would agree. It makes perfect sense on an Optima.

 

[LFMarm]

If you change that to say Optima CM then I would agree. It makes perfect sense on an Optima.

It is indeed for a CM.

Out of curiosity, why it doesn’t make sense for the BM unit? I would have assumed that the same considerations translate to that one.

 

[Tracy]

It is indeed for a CM.

Out of curiosity, why it doesn’t make sense for the BM unit? I would have assumed that the same considerations translate to that one.

It allows the BM unit to offboard diluent and feed the BOV from an acceptable gas volume and mix.