Unbalance SCR regs
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deepblueh2o
Guest
It's not disregarded, it's used as a method for controlling maximum diver depth. At about 230 feet you zero out the flow on a Draeger.
deepblueh2o:
Thanks, that really helps me understand the limits. Since I like to sometimes dive deeper than 230, I guess I need a different method. Is there information on what happens when a balanced first stage is used? Are there problems with the Sonic orifice? I have been looking at the KISS modification to CCR which does look like an elegant solution. In general, I like to dive Trimix anyway (diluent) and I am mostly interested in the characteristics of the dosing device for the nitrox/oxygen.
deepblueh2o
Guest
You could always buy a different orifice for your deep dives and use trimix as your bottom mix. Manual oxygen addition or manual bottom mix dilution would adjust the mix as needed. I routed around the problem by replacing the first stage with a depth compensated, using a smaller orifice, and then changing my gas mix.
You are going to end up carrying those extra tanks anyway, for bailout at depth.
You are going to end up carrying those extra tanks anyway, for bailout at depth.
swisstrav
Contributor
are you guys sure you know what you are doing? why do you want to change your orifice? properly matched to your intermediate pressure, there is no need to change.
when a balanced first stage is used, your oxygen flow will increase while descending.
this brings your ppo2 to dangerous levels, above 1.4-1.6 bar approx. 20psi. remedy would be, adding diluent gas to your system or switch over to your bail-out.
in order to get a constant flow, first stage is not balanced.
if inside pressure in your counter-lungs equals the outside pressure, applied by the surrounding water, your oxy-flow will come to a standstill.
your depth limits are directely related to the intermediate pressure. for that reason drager uses on dolphin/ray a higher pressure (14.5 bar/220psi vs about 9-10 bar on oc-equipment at sealevel).
deepblueh2o you are just wasting oxygen/diluent gas by increasing your flow. oxygen consumtion (metabolism) has nothing to do with the depth, rather with your body (work load, stress factor etc). as a rule of tumb the consumption with easy flying should be somewhere between 0.8 to 1 liter/min. ideal is a flow/orifice size which ist just a little bit below your consumption. that means, from time to time you manually need to add oxygen (kiss-valve).
for that reason the partial pressure of oxygen has to be monitored by at least 2 independent systems.
before you guys go to the depths desired, make sure you fully understand the system and what you are doing. those machines are fun to fly with and give you the utmost freedom in diving.
BUT THEY CAN ALSO KILL YOU WITHOUT ANY WARNINGS IF NOT HANDLED IN THE RIGHT MANNER
sorry for my spelling
swisstrav
when a balanced first stage is used, your oxygen flow will increase while descending.
this brings your ppo2 to dangerous levels, above 1.4-1.6 bar approx. 20psi. remedy would be, adding diluent gas to your system or switch over to your bail-out.
in order to get a constant flow, first stage is not balanced.
if inside pressure in your counter-lungs equals the outside pressure, applied by the surrounding water, your oxy-flow will come to a standstill.
your depth limits are directely related to the intermediate pressure. for that reason drager uses on dolphin/ray a higher pressure (14.5 bar/220psi vs about 9-10 bar on oc-equipment at sealevel).
deepblueh2o you are just wasting oxygen/diluent gas by increasing your flow. oxygen consumtion (metabolism) has nothing to do with the depth, rather with your body (work load, stress factor etc). as a rule of tumb the consumption with easy flying should be somewhere between 0.8 to 1 liter/min. ideal is a flow/orifice size which ist just a little bit below your consumption. that means, from time to time you manually need to add oxygen (kiss-valve).
for that reason the partial pressure of oxygen has to be monitored by at least 2 independent systems.
before you guys go to the depths desired, make sure you fully understand the system and what you are doing. those machines are fun to fly with and give you the utmost freedom in diving.
BUT THEY CAN ALSO KILL YOU WITHOUT ANY WARNINGS IF NOT HANDLED IN THE RIGHT MANNER
sorry for my spelling
swisstrav
deepblueh2o
Guest
Swisstrav is right about the first stage, I rechecked my configuration. My appologies for that. When mine was semi closed I used the smallest draeger jet, and reduced my nitrox mix. I also installed a loop flush. It worked great. Loop flush was required to breathe mix at surface if needed. I also used a seperate bailout system.You're not wasting bottom mix on a semi it's going anyway.
swisstrav
Contributor
@ deepblueh2o
what kind of set-up are you diving at the moment?
with semi closed, what mix did you use down deep and did you monitor pp o2?
about myself. yes i dive rebreather too (dolphin) and im in the process of investing in such a toy. i know it will be ccr. at the moment evaluating inspiration or dolphin rebuilt.
tendency goes towards dolphin. pricewise both are approx. the same.
must have: composite bottles 2 or 3 liter (airfare)
o2 integrated computer
small booster pump (thats another story)
diving:
i do not dive the lakes here in switzerland. to cold, no viz, nothing to see.
so its always somewhere in the tropics or for us very convenient: the red sea.
my interests are in photography.
i have dived:
florida owd
florida aowd
maldives
red sea
indian ocean (emirates)
philippins
yap
palau
on my list is:
bonaire
ruotan (bay islands)
sudan
jemen
bikini-atoll (only with rebr)
my dream is:
travelling around the world and do all those great dives. 6 months +
have i disclosed to much about myself ?
see you down there
swisstrav
what kind of set-up are you diving at the moment?
with semi closed, what mix did you use down deep and did you monitor pp o2?
about myself. yes i dive rebreather too (dolphin) and im in the process of investing in such a toy. i know it will be ccr. at the moment evaluating inspiration or dolphin rebuilt.
tendency goes towards dolphin. pricewise both are approx. the same.
must have: composite bottles 2 or 3 liter (airfare)
o2 integrated computer
small booster pump (thats another story)
diving:
i do not dive the lakes here in switzerland. to cold, no viz, nothing to see.
so its always somewhere in the tropics or for us very convenient: the red sea.
my interests are in photography.
i have dived:
florida owd
florida aowd
maldives
red sea
indian ocean (emirates)
philippins
yap
palau
on my list is:
bonaire
ruotan (bay islands)
sudan
jemen
bikini-atoll (only with rebr)
my dream is:
travelling around the world and do all those great dives. 6 months +
have i disclosed to much about myself ?
see you down there
swisstrav
Clearly, I don't have all the answers - if I did I would not ask questions. I am diving the Drager SCR, but I am exploring the KISS modification to make it CCR. I realize that there is risk of death if I don't have the proper amount of oxygen, that is why I am interested in understanding better the Sonic orifice,the unbalanced first stage and depth. My problem is understanding why, if the Sonic orifice stops flowing at 230, (which clearly indicates that ambient pressure affects the dosing device), that you would not benefit by compensating for that change in ambient pressure. I am guessing that the relationship is not linear and that the curve must do something strange.
I use an Oxyguage and if I were to dive deep, I would add a VR3 or HS Exlorer. Sorry to sound ignorant, I am just hoping to learn.
I use an Oxyguage and if I were to dive deep, I would add a VR3 or HS Exlorer. Sorry to sound ignorant, I am just hoping to learn.
swisstrav:
Walt StarkIII is the man to arrange Rebreather and Technical diving in Bonaire. Check out www.rectecscuba.com
swisstrav
Contributor
questions were for deeplueh2o. i can not imagine that he is on the save side.
it does not sound ignorant at all.
where do i start?
in the earlier post i have written about the metabolizm already. bear in mind, your body needs approx. 1 liter of oxygen per minute.
on a kiss system, you need a steady flow of o2 which is just a little under the rate you are using up. this ist done by the orifice which is nothing else than a metering device.
the orifice has a fixed bore (approx. 7/1000 in). as long as you are feeding a medium on a given pressure, you will get a stady flowrate on the other side of the orifice.
if you now increase pressure (bore diameter still the same) you will get a higher flow rate. a higer flow rate results in more oxygen in the system, thus bringing your o2 to dangerous levels (higher than 1.4 - 1.6 bar pp o2)
thats the reason why you need to modify your first stage or use a drager 1st. stage.
your intermediate pressure ist directely related to the possible theoretical depth. with a intermediate pressure of 14.5 bar (absolute) deduct 1 bar for ambient pressure = 13.5 bar. 1 bar equals a watercolumn of 10 meters.
10 x 13.5 = 135m/443ft.
at a depth of 443ft your gasflow comes to a stop. i would guess, by reducing your mod (max. operation depth) by 10 to 25% you are on the safe side.
however, bear also in mind, anything below 130ft should be on trimix/heliox as a diluent. on top of that you need to think about your bail-out too.
i hope i have clarified the system. if you have more questions im glad to help as long as i can.
swisstrav
it does not sound ignorant at all.
where do i start?
in the earlier post i have written about the metabolizm already. bear in mind, your body needs approx. 1 liter of oxygen per minute.
on a kiss system, you need a steady flow of o2 which is just a little under the rate you are using up. this ist done by the orifice which is nothing else than a metering device.
the orifice has a fixed bore (approx. 7/1000 in). as long as you are feeding a medium on a given pressure, you will get a stady flowrate on the other side of the orifice.
if you now increase pressure (bore diameter still the same) you will get a higher flow rate. a higer flow rate results in more oxygen in the system, thus bringing your o2 to dangerous levels (higher than 1.4 - 1.6 bar pp o2)
thats the reason why you need to modify your first stage or use a drager 1st. stage.
your intermediate pressure ist directely related to the possible theoretical depth. with a intermediate pressure of 14.5 bar (absolute) deduct 1 bar for ambient pressure = 13.5 bar. 1 bar equals a watercolumn of 10 meters.
10 x 13.5 = 135m/443ft.
at a depth of 443ft your gasflow comes to a stop. i would guess, by reducing your mod (max. operation depth) by 10 to 25% you are on the safe side.
however, bear also in mind, anything below 130ft should be on trimix/heliox as a diluent. on top of that you need to think about your bail-out too.
i hope i have clarified the system. if you have more questions im glad to help as long as i can.
swisstrav
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