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View Full Version : Off-board gas for SHTF only?



mrmints
31-03-2016, 01:20 PM
This is not something I really need to worry about at the moment, but it interests me...

What circumstance might you want to plumb in some off board gas, that isn't an "it's all gone wrong" scenario?

I have a MAV for the diluent side of my KISS Classic, that I might put on in the future and it has the option of external gas. Now seeing as this external gas could only ever go into the loop (not the BOV) via the MAV, I thought there must be some legitimate need...

Thanks,

Chris

Capt Morgan
31-03-2016, 02:18 PM
I also fitted a second MAV to my unit with a BCD type fitting but it's fed from inboard dil
and is only for dil flushing as I'd much rather use the ADV to add gas.
I also have the same fitting on my secondary O2 so it can to use as a back up on
longer/deeper dives. Offboard deep BO is straight to the BOV so can be used to add gas to the loop.
The MAV could also be used to run the unit at depths where the O2 IP drops to much on the unit but
I think this is best sorted by changing the orifice and spring, my unit is running an IP of 16bar.

Dave1w
31-03-2016, 03:42 PM
Mine has a revo gas block, which allows you to add offboard gas to the 3rd button. I've found in holidays sometimes, it's easier to run dil from offboard and get that topped up than taking off your onboard dill tanks for a fill.... Yes laziness! Also sometimes, I know the air in MY dil tank is clean clean, but filling it for a compressor at a centre may just be normal, so if I can avoid having to refill my dil I do.

Then again, some time you may just run out of dil, or o2?




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ebt
31-03-2016, 04:49 PM
Dil switching is still seen as valid on some of the really big dives, other than that theres the SCR option. Cant think of anything else right now.

jturner
31-03-2016, 04:50 PM
Bearing in mind my unit isn't a KISS (it's an APD Evo), I like having offboard gas available to connect to the MAVs in case of:


Loss of diluent or O2 due to excess use or leakage. My rich stage is typically rich enough to double as O2. I have run very low on dil once (~30bar @ 25m but with 20mins of stops left) due to a cell problem during a 3 hour dive. Plug in offboard, shut ADV and leave the onboard for wing inflation only.
Backup supply in case of needing to shut down the onboard eg hose failure, stuck solenoid. Yes, I could feather the O2 on and off but why bother when you have offboard? Keep that pantomime in reserve just in case! As previously mentioned, my rich stage is typically rich enough to double as O2 via the MAV.
Lots of known gas available in case of needing to do a BIG or repeated flushes for some reason. 2L cylinders take a kicking doing a proper flush at 35m let alone 60m... that's how I ran low.
Lots of gas available for doing SCR mode (but I'd really have to want to do this...).


YMMV and all that, but it is quite a bit of flexibility for little extra complication/failure points IMHO. Options are nice...!!!

notdeadyet
31-03-2016, 08:30 PM
I had an offboard hose on my KISS. Never used it in the 4 years I owned it, it was only because it was a braided 200bar hose that I left it on.

The only real reason I'd ever think of doing it is to SCR a long way out. I prefer having as few unnecessary connections as possible into the loop. It's a hassle but I can SCR using the BOV (and it's slightly easier on the lungs) rather than adding extra bits.

The KISS was meant as a minimalist unit, I fannied about with mine a lot and in the end I just had a straight, basic, stock unit with all the shite stripped off and flogged.

mrmints
03-04-2016, 10:44 PM
Thanks for all the responses...seems that unless you're doing massive dives, it's really to get you out of trouble.

Capt Morgan
03-04-2016, 11:18 PM
It's probably best to keep it simple ;)
I only fitted the second MAV because
I'm doing what I consider some big dives
and like to have an O2 backup if needed,
as it's fitted I just have dil connected to it
but in reality I would rather not have it on
90% of my dives, it's just another failure
point.

Paulo
04-04-2016, 06:06 AM
It's probably best to keep it simple ;)
I only fitted the second MAV because
I'm doing what I consider some big dives
and like to have an O2 backup if needed,
as it's fitted I just have dil connected to it
but in reality I would rather not have it on
90% of my dives, it's just another failure
point.

You will need it for Lucy

Major Clanger
04-04-2016, 06:52 AM
I used off board gas for the deeper part of a deep dive when my dil wasn't suitable for beyond 60m. Three quarters down the shot flushed using off board.







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Paulo
04-04-2016, 06:54 AM
I used off board gas for the deeper part of a deep dive when my dil wasn't suitable for beyond 60m. Three quarters down the shot flushed using off board.

Why choose an unsuitable dil for inboard?

Major Clanger
04-04-2016, 06:56 AM
Why choose an unsuitable dil for inboard?

I didn't, it was already there for a shallower dive that didn't come off. It's no biggie, squirt it in from one place instead of the other.