Many rEvo divers I know have a love/hate relationship with the Automatic Diluent Valve (ADV). It is nice to have especially when you are trying to do a quick descent and might be task loaded. However, it always seems to fire at the most inopportune time and then adds diluent to your loop when you are trying to maintain a PO2 on deco AND adds buoyancy. Or you are navigating through a wreck, move into a slightly odd position which then shifts the gas in your counterlungs and the ADV fires — once again affecting your buoyancy and your loop PO2.
Many other rebreathers actually have this feature built-in. The rEvo has the ADV inside the unit in the exhale counter lung so it isn’t so easy to add a shutoff valve.
My ideal situation would be to have the ADV “on” during my descent and then “off” during the dive and the ascent.
The first solution, and the one that I know quite a few rEvo divers use, is to simply turn off the ADV before the dive. Again, because the ADV valve is inside the unit and not accessible during a dive, this is a “black and white” configuration option and cannot be changed during a dive so it doesn’t really meet my needs.
The second solution is to “tune” the ADV valve such that it only fires when you really bottom out the lung and pull in a large breath. I’ve tried tuning my ADV for probably 20-30 dives and couldn’t ever get it the way I wanted such that it fired on the descent but not thereafter.
I went in search of other solutions that involved adding a shutoff valve that I could manually control during the dive.
ADV Shutoff – Version 0
My first “solution” to this problem was simply to shut off the diluent tank valve!
This actually worked reasonably well but had a couple downsides:
- If I needed to inflate my BC for whatever reason, it required me to first remember to turn on the diluent tank valve
- If I did need to dilute my loop gas, once again, I would have to first turn on the diluent tank valve
This really wasn’t a big problem, but was far from idea. Ideally, I would be able to isolate JUST the ADV supply and not everything connected to the diluent tank.
ADV Shutoff – Version 1
A standard rEvo supplies the ADV valve from a hose that goes from the diluent first stage to a coupling in the housing (which then goes to the ADV valve in the exhale counterlung). The first stage (and the ADV feed hose) is at the bottom of the frame on the back of the unit.
My first attempt at a ADV involved simply putting a shutoff valve inline:
ADV Shutoff, Version 1
Shutoff valve inline
This was a great concept. It was simple, easy to reverse, cheap to implement, etc. However, it had the big disadvantage of not being able to be changed mid-dive easily. I tried for 4 or 5 dives to reach back and change the shutoff valve. Either because of the diluent tank itself, my bailout tank or something else, I really couldn’t easily operate the shutoff when it was in this location.
Back to the drawing board….
ADV Shutoff – Version 2
I have to admit, I was not the first to come up with this idea. There were various posts to Rebreatherworld about similar setups but it wasn’t clear how people did them. This is the way my unit is currently configured.
First, it might help to have a “line diagram” of how the rEvo gas supply works from the diluent supply:
The solution I implemented involves splitting the gas supply after the T-Connector as it flows into the BC. Here is what the modified line diagram looks like:
- OmniSwivel Adapter: 3/8″ Male to BC Inflator QD Post ($24.99)
- OmniSwivel Reversible Inline Shutoff Valve: 3/8″ Male to 3/8″ Female ($53.99)
- OmniSwivel LP Y-Block: 2 Port 3/8″ Female to 1 Port 9/16″ Female ($35.99)
- DGX Adapter LP Reg Hose into BC Inflator Hose ($10)
- 90 Degree Swivel Adapter 9/16″ Male to 9/16″ Female ($10)
- Miflex hose – Unsure of Length
Here are a few pictures that show how the system looks during assemble and when finished:
There was some confusion about the setup, so I’ve included two additional photos below. One of them is labeled and shows the hose routing and the other is a view of the setup on my wing.
I like the new system and it works well. Sometimes I forget to “reset” the shutoff to “on” between dives so I have to either use the MAV or push the shutoff down to turn it back on. I also have incorporated testing the ADV shutoff into my build process.
8 thoughts on “rEvo ADV Shutoff”
I’d love to know how this has worked for you? I used tour guide to install my own adv shut off. I found that the 90 puts my hose in a bad spot where the tank puts strain on the hose crimp. I’m going to try eliminating the 90 to see if that puts less strain on the hose. I’ve also noticed it makes the power inflator hard to bend enough to get it in my mouth to oral inflate.
On a second note related to your other post, what size o rings did you use for the o2 hose mod you got from Mel? Mine also has this and I’d like to get an o ring on it.
I appreciate your blog. I am a brand new rebreather diver and it is helpful!
Thanks for your comments!
The ADV disconnect system has been working well.
I have not had a problem with the 90 degree connector at all. In fact, I think it helps keep it streamlined. One possible reason is that I have different tank brackets (but I don’t think that is it).
In terms of o-rings, I’m not sure exactly which ones you are referring to? Do you mean the one on the MAV that prevents the quick disconnect from getting accidentally disconnected? If so, I think I just tried a few different ones until I found one that fit in the groove. I’ve also recently modified it a little bit to make it easier to pop them off with dry gloves.
I will email you photos of the new MAV setup and also the 90 degree connector detail since maybe we are doing it differently.
First off, thank you for sharing your adventures and technical knowledge.
I just completed installing the ADV shutoff system on my rEvo micro expedition. Very anxious to try it out in a couple weeks down in Roatan.
I found your pics and instructions very complete and with the addition of a 32″ hose I’m ready to go in a couple weeks.
You are very welcome, just remember that isn’t a “factory approved” modification.
Just had to include your cheesey doodles in the picture 🤣
Haha! Yup. Hope you are doing well, John.
Brett, thanks for posting the diagrams, multiple previously attempted versions and the parts list for your inline ADV shutoff. I ordered the parts from DGX, sans the hose expecting I’d need to measure to length (looks like 31”). Unfortunately I can’t seem to figure out how the 90 degree fits on the rEvo, where the previous 6” host ran from the DIL reg into the ADV Via the 3/8” male QD post. If I remove the post the 9/16” male to female doesn’t fit in that fitting (not to mention I don’t think there’s room to spin it on in the position on my rEvo micro). Can you add a picture of what your ADV to hose connection is on your setup? Thanks!
Hi John. I will be away from my rEvo for about a week so I will try to remember to send pics after that.