BOV OC Strategy...

jhaaja · 25th January 2007, 13:03

Quote: (Originally Posted by Peter Piemonte)

True enough. I usually dive with 19cf tanks. I guess I am planning for that to be adequate to get my breathing under control prior to making the switch. Even doubling my normal RMV, I would have about 5 minutes to get my breathing under control at 200'. In any event, having a BOV under this circumstance is infinatly better than not, as going open loop on an ADV presents a high work of breathing. At least on my unit.
I believe in the KISS principle. I do not like the complexity and failure points added by gas blocks and connectors. I also do not think a diver compromised by a CO2 hit can be trusted to connect and turn on these devices.
When diving open circuit, we made gas switches all the time. It is a normal part of decompression diving. Once your breathing is under control the ascent is almost normal. I do think your meathod of having it plumbed from the start in is very good however. Peter

The key point is that I have the bail out plugged to the BOV all the time. Now fiddling when under water. I do not have any swich blocks etc. Just LP-hose connecting the BOV via quick connects to the bail out tanks 1st stage.

BOV is a good thing to have that is for sure.

silent running · 26th January 2007, 01:27

Thanks for the info guys. It seems that the only reason you'd have to come off the BOV/OC is a BO gas switch. In SCR mode, switching out the cylinders with QCs wouldn't be a problem, but I'm guessing it's not really possible if you're in full OC mode and breathing off the BOV 2nd stage and trying to switch from 1 mix to another on the fly. I've never had a BOV and the OC multiple gas switch problem was not something I had thought of. So you just come off the BOV and use the next mix 2nd stage, OK.

But in the event of doing an SCR BO, and then using the QC to switch mixes, is the water that gets in the line harmful to the 2nd stage downstream?

silent running · 26th January 2007, 01:37

Quote: (Originally Posted by Padowan)

I have a Divematics BOV, connected through an AP GCS hose to my offboard. Have breathed it (as a test, not in anger) at 70m, and it breathes OK - not as nice and smooth as a normal 2nd stage, but fine. I think the change in characteristic is based on the 90 degree flow path and sharp corners that the gas must take as the WOB is the same inhaling and exhaling.

Thanks for the info Padowan, this makes sense, the 90 degree angles causing some additional resistance, but not enough to make a big diff. I wonder if any of the BOV manufacturers have managed to minimise those hard angles in the OC mode pathway...

jhaaja · 26th January 2007, 05:26

Quote: (Originally Posted by silent running)

Thanks for the info guys. It seems that the only reason you'd have to come off the BOV/OC is a BO gas switch. In SCR mode, switching out the cylinders with QCs wouldn't be a problem, but I'm guessing it's not really possible if you're in full OC mode and breathing off the BOV 2nd stage and trying to switch from 1 mix to another on the fly. I've never had a BOV and the OC multiple gas switch problem was not something I had thought of. So you just come off the BOV and use the next mix 2nd stage, OK.

But in the event of doing an SCR BO, and then using the QC to switch mixes, is the water that gets in the line harmful to the 2nd stage downstream?

I say no, because the amount of water is so small. Might be a good idea to flush salty sea water out from the hose and 2nd stage after the BO fun

The amount of water getting in Swagelok QC6 series is 1 cm3, I checked it out to be sure.

Can be found in the pdf on page 3.
http://www.swagelok.com/downloads/we.../MS-01-138.pdf

Mdemon · 26th January 2007, 11:10

I second most of what the others said above; offboard bailout plumbed into the BOV (via APD's GCS) so you can operate it and forget it until it's time to switch to deco gas.

I've experimented with switching gas via the GCS underwater and it's very hard work - although it is possible. I think we all concluded that an easier way is to switch the BOV to OC and ascend on it. At switch time you should be calm enough to take the BOV out and replace it with the normal second stage from your deco tin. This was how I dived mine although I did have GCS fittings on all regs in case I felt like keeping the BOV where it is. I think for most bailouts I would have been trying to get back onto the loop rather than switch gases but at least I had the option.

I think a decent second stage is a must and any manufacturer making a BOV really should put an excellent second stage reg on it or allow the end user to fit their own. One of my projects is to retro-fit an ATX50 or 100 to my Bob H BOV having switched (in anger/mildly annoyed) to the BOV's Dacor Viper at 130m. Workable, but WOB like breathing through your clenched fist. Going back to my loop was a pleasure.

25th January 2007, 13:03	#11 (permalink)
jhaaja Custom Title Allowed! Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Mar 2005 Location: Finland Posts: 884	Re: BOV OC Strategy... Quote: (Originally Posted by Peter Piemonte) True enough. I usually dive with 19cf tanks. I guess I am planning for that to be adequate to get my breathing under control prior to making the switch. Even doubling my normal RMV, I would have about 5 minutes to get my breathing under control at 200'. In any event, having a BOV under this circumstance is infinatly better than not, as going open loop on an ADV presents a high work of breathing. At least on my unit. I believe in the KISS principle. I do not like the complexity and failure points added by gas blocks and connectors. I also do not think a diver compromised by a CO2 hit can be trusted to connect and turn on these devices. When diving open circuit, we made gas switches all the time. It is a normal part of decompression diving. Once your breathing is under control the ascent is almost normal. I do think your meathod of having it plumbed from the start in is very good however. Peter The key point is that I have the bail out plugged to the BOV all the time. Now fiddling when under water. I do not have any swich blocks etc. Just LP-hose connecting the BOV via quick connects to the bail out tanks 1st stage. BOV is a good thing to have that is for sure.
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26th January 2007, 01:27	#12 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,814	Re: BOV OC Strategy... Thanks for the info guys. It seems that the only reason you'd have to come off the BOV/OC is a BO gas switch. In SCR mode, switching out the cylinders with QCs wouldn't be a problem, but I'm guessing it's not really possible if you're in full OC mode and breathing off the BOV 2nd stage and trying to switch from 1 mix to another on the fly. I've never had a BOV and the OC multiple gas switch problem was not something I had thought of. So you just come off the BOV and use the next mix 2nd stage, OK. But in the event of doing an SCR BO, and then using the QC to switch mixes, is the water that gets in the line harmful to the 2nd stage downstream?
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26th January 2007, 01:37	#13 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,814	Re: BOV OC Strategy... Quote: (Originally Posted by Padowan) I have a Divematics BOV, connected through an AP GCS hose to my offboard. Have breathed it (as a test, not in anger) at 70m, and it breathes OK - not as nice and smooth as a normal 2nd stage, but fine. I think the change in characteristic is based on the 90 degree flow path and sharp corners that the gas must take as the WOB is the same inhaling and exhaling. Thanks for the info Padowan, this makes sense, the 90 degree angles causing some additional resistance, but not enough to make a big diff. I wonder if any of the BOV manufacturers have managed to minimise those hard angles in the OC mode pathway...
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26th January 2007, 05:26	#14 (permalink)
jhaaja Custom Title Allowed! Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Mar 2005 Location: Finland Posts: 884	Re: BOV OC Strategy... Quote: (Originally Posted by silent running) Thanks for the info guys. It seems that the only reason you'd have to come off the BOV/OC is a BO gas switch. In SCR mode, switching out the cylinders with QCs wouldn't be a problem, but I'm guessing it's not really possible if you're in full OC mode and breathing off the BOV 2nd stage and trying to switch from 1 mix to another on the fly. I've never had a BOV and the OC multiple gas switch problem was not something I had thought of. So you just come off the BOV and use the next mix 2nd stage, OK. But in the event of doing an SCR BO, and then using the QC to switch mixes, is the water that gets in the line harmful to the 2nd stage downstream? I say no, because the amount of water is so small. Might be a good idea to flush salty sea water out from the hose and 2nd stage after the BO fun The amount of water getting in Swagelok QC6 series is 1 cm3, I checked it out to be sure. Can be found in the pdf on page 3. http://www.swagelok.com/downloads/we.../MS-01-138.pdf
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26th January 2007, 11:10	#15 (permalink)
Mdemon SiegeEngine II Current Rebreather/s: Inspiration Classic Home Build Other Rebreather/s: Inspiration Classic Home Build Join Date: Feb 2007 Location: SWUK Posts: 1,906	Re: BOV OC Strategy... I second most of what the others said above; offboard bailout plumbed into the BOV (via APD's GCS) so you can operate it and forget it until it's time to switch to deco gas. I've experimented with switching gas via the GCS underwater and it's very hard work - although it is possible. I think we all concluded that an easier way is to switch the BOV to OC and ascend on it. At switch time you should be calm enough to take the BOV out and replace it with the normal second stage from your deco tin. This was how I dived mine although I did have GCS fittings on all regs in case I felt like keeping the BOV where it is. I think for most bailouts I would have been trying to get back onto the loop rather than switch gases but at least I had the option. I think a decent second stage is a must and any manufacturer making a BOV really should put an excellent second stage reg on it or allow the end user to fit their own. One of my projects is to retro-fit an ATX50 or 100 to my Bob H BOV having switched (in anger/mildly annoyed) to the BOV's Dacor Viper at 130m. Workable, but WOB like breathing through your clenched fist. Going back to my loop was a pleasure. __________________ www.southwestmafia.com "Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?" Last edited by Mdemon : 26th January 2007 at 11:27.
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