Dangerous Azimuth scrubber

jaap

Hi

I have had two CO2-hits and a few cases of what I belive to be CO2-issues that forced me to go semi closed (converted to MCCR) with my Azi-scrubber. This lead me to not use the Rebreather-with confidence. I finally stopped using it about 1,5 years ago.

Around that point I had gotten some info about others experiencing CO2 bypass in their Azi-scrubbers via Rebreather World, thanks Joseph! A simple test revealed that my scrubber was indeed bypassing gas.

Quick test: Open empty scrubber. Pour a cup of water into the water trap via the exhale entry, make sure not to let any spill out into the center tube. Seal the exhale entry, like with a rubber bung, the cap that comes with it or in worse case with your palm. Turn the scrubber around so that the water is still in the trap but pooling against the wall to the sorb side, making sure no water escapes through the center tube. Slowly rotate the scrubber at least one revolution while checking that no water makes it over to the inhale/sorb side. If any water leaks over you either have a defective scrubber or put in too much water so that it escaped via the center hole.

If the scrubber passes this test there is another thing to watch out for. I had noticed a patchy pattern of more CO2 issues when the scrubber was packed tight (yes I know about the loose vs tight pack threads).

This test is a bit more complicated. Insert some large ID pipe of the apropriate lenght into the scrubber an push hard on the bottom while repeating the above test of rotating with some water. Repeat pressing on the center tube. These tests are to simulate the pressure of the lid springs via a packed scrubber on the compartment wall. Its possible that the bypass opens or enlarges when the scrubber is packed!

Since the scrubber is extremely sturdy there was no way for me to open the water trap compartment or to tear away the stainless mesh, at least not in a reversible way. Since the whole thing is TIG-welded (I believe) and I have extremely limited welding experience I had to get help. After quite some time the opportunity appeared to pass it on to a machinist willing to take a look at it, thanks Andreas!

The thing lay around for a while before the exhale end was recently cut open on a lathe, a million thanks Mattias! FOTO

It turned out that the wall that separates the water trap (exhale) from the radial sorb compartment was only attached with six spotwelds against a lip on the inside of the outer wall of the scrubber! So some gas and water for that part could sneak by from the exhale side right to where the mesh is at the inhale side, effectively bypassing the sorb....

If the compartment wall is pushed by the springs via a packed sorb the gap could enlarge!

The scary thing is that I did dives with 20-30 min deco, dives to max 46 m, some icedives, sometimes pushing the scrubber to around 240 min total with no issues. Thinking back there was a trend that the problems got worse towards the end so it could be that the gap grew over time...

Anyway the spotwelds were replaced by a continous weld seam closing the bypass possibility and the end was welded back on.

The spot welds can be seen on this picture:
FOTO

If anybody opens up their scrubbers, don't blame me if it gets ruined in the process. And don't forget to inspect the weld were the center tube penetrates the wall.

I have heard that this very odd and most dangerous construction was only used on a few older Azimuth scrubbers... Lets hope its very rare.

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Dave Sutton

Excellent post, and excellent work. I have 4 Azi's in the shop right now of various ages, and I'll make a study later tonight to see if I can observe any external evidence that would let a diver know if he has a spot welded can or a continuously welded can. Failing that, the easy way is to simpy haul it down to your local NDT shop for an X-Ray. Testing by the methods you suggest ought to be done by everyone. The fix looks scary but ought to not be difficult with a lathe and a good TIG welder. Any decent machine shop ought to be able to do it.

Well done, and thanks for sharing.


Dave

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PaulTG2

Hello,

An excellent, excellent posting and a must-read for Azi scrubber owners. I know I'll check mine out. However, it would seem that this might be more easily checked with a bore scope instead of having to cut it open. I wonder if there is a sealer that could be used to seal around the wall without having to open it... perhaps with a bore scope and bendable tube to apply the sealant? Anyone have any ideas?

-p

Dave Sutton

Proseal 895 is a flexable aerospace sealant with exactly the right specs. If I need to seal one, that's what I'll use. Fuel & hydraulic fluid resistant. Excellent stuff. This is not your common sealant.


Aerospace Sealant Chart by Bergdahl Associates, Inc.

"Pro-Seal 895 Aerodynamic Smoothing Sealant
Description P/S 895 Class B is an aerodynamic smoothing sealant. It has a service temperature range from -65°F (-54°C) to 250°F (121°C), with intermittent excursions up to 275°F (135°C). This material is designed for sealing aircraft structures and pressurized cabins or for depression filling and smoothing applications. The cured sealant maintains excellent elastomeric properties after prolonged exposure to both jet fuel and aviation gas.
P/S 895 Class B is a two-part, manganese dioxide cured, polysulfide sealant. The uncured material is a low sag, thixotropic paste suitable for application by extrusion gun or spatula. This sealant has excellent adhesion to common aircraft substrates."





Dave

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jaap

Dave and Paul, thanks for the compliments.

One can most likely see the welds looking into the exhale opening with the proper light. Perhaps with an inspection mirror and small LED?

I pondered using some sealant but decided it would be best to have it welded. Remember the compartment wall can possibly move a little when the sorb is compressed. Good tip about the sealant Dave! I know there are a million speciality glues/sealants never heard of by the average consumer. Just make sure its compatible with very high pH (normally not a big issue)

A friend of mine had a nasty small hole in the soldering in the top of an IDA-76 scrubber between the two compartments effectively making a small bypass. If I recall correctly it took a small inspection mirror and light to see it. Anyway it was sealed by the use of a long syringe and some sealant (don't remember the make).

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SeaBass

Thanks for the post. This type of post is exactly why this forum contains invaluable info!

Dive safe.

--SB

TPAD

Hi
I read this some time back and tested mine with water ---- aaarrrg !!
on cutting the scrubber open only 4 small tacks held the baffle in place - water and co2 had a direct path to the inhale side,
i think a continuous Tig welds best - the gaps on mine were upto 3mm wide - will sealant plug that ?
regards
Tim

jaap

I guess you will perhaps be contacted by someone related to the Azimuth manufacturing. If not please pm me you email if you want to be contacted.

If I was you I would not feel comfortable with the sealant option. If you cut it open you would have to weld on it anyway?

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Dave Sutton

There should probably be a manufacturer sponsored recall on all of these scrubbers.

JAAP: Any contact with them? I still have three to check, just have not had a moment to look.


Pro-Seal will seal 3mm with ease... but this *should* be taken care of by the MFG, as it's a clear design defect.


Dave

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caver99

Hi Dave,

I just contacted them, lets see what the answer will be .
In the past the were always friendly and helpfull (to me...no idea in the US, maybe different distributor over there)

As far as I have more I will post it of course.

Greetings
Martin

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