Rusty C370 sleeve

[stepfen]

As mentioned in another post I just finished servicing my first ever C370.
I fount disassembling and assembling it quite straight forward (contrary to discussions I have seen eg in Scubapro C370 service manual? ).

What bothers me though is the condition of the metal sleeve (part no 33 in the schematics).
This is how the sleeve assembly was when I took it out:

Here is the sleeve after cleaning it:

The "dirt" inside the grove is corrosion and groove's surface is not smooth any more. Also notice the permanent (?) discoloration of the (otherwise) smooth outer sleeve surface. I couldn't clean it any further.

Here are my questions: How critical are these? Are these sleeves made of so crappy material, or is there something wrong with this particular one? Is there something that can be done to fix this now and/or are there any preventing measures to stop the corrosion growing even further?

A bit of background info: I bought this reg new in summer 2019. As it has been working flawlessly since then (about 280 dives all in salty water), and to be honest a bit scared after reading the disassembly/assembly difficulties other divers had, I have been postponing servicing it until now. During that time the care it was receiving was this: Within an hour since the last dive of the day (regs still mostly wet) it was submerged in fresh water for about 10-20 minutes and then rinsed with a garden hose. Then hanged to dry and stored in the basement. Exception was during 3 one-week-long diving trips/LoBs were it was not rinsed/cleaned with fresh water for a week at a time. Ok, for sure it is NOT the most well taken care off reg in the world, but I dare to say that it was not too bad taken care off either.

Thanks for any feedback.

 

[axxel57]

Did you dive steel tanks in that time?
And how looks the filter of your first stage?

 

[rsingler]

Much like the piston base in a Mk10, trapped seawater does a slow job of corrosion that yields the rust you show there, @stepfen.
In your case, it's not dissimilar metals corrosion where there's galvanic action, but rather, just slow rusting of steel that's not truly "stainless".

That knob design is troubling, because the tolerances are so tight. I think your post dive care is just fine. There are trips where things just stay wet for days. The only suggestion I have is that given what you have there, I'd soak a second time in fresh water overnight, after your initial 20 minutes, before hanging them up to dry. You need time for diffusion down those tiny spaces to decrease the salt concentration.

As for the pits in the sealing land for that fitting, since it's outside any high pressure gas pathway, I'd use some old fashioned thick silicone grease to fill the irregularities under the new oring, so the case stays sealed. It'll probably still be there two years from now.

 

[rsingler]

For some subtle evidence supporting the problem of trapped seawater, look at the sealing o-ring for the adjuster mechanism inside:

On the external side of the adjuster, where the space under the knob is more easily rinsed during soaking, the plastic is black.
On the internal side, where the threaded mechanism traps seawater behind the balance chamber, the nearby stainless steel sleeve adds rust to the water which gets deposited, just like the trapped water on the outside of the sleeve.

Apart from diving in fresh water, there is no way to use pressure to force molecules of fresh water into the mechanism. Left only with diffusion, it takes lots of time.

A disappointing design flaw in an otherwise superb regulator. Perhaps a quick disassembly and cleaning every six months? You wouldn't really even have to replace the orings.

The A700 has the same damned problem:

Scubapro loves to use parts from other systems in new designs, to save development cost. They should have left this one in the drawer.

 

[stepfen]

Thanks Robert. Everything you say makes perfect sense.

Did you dive steel tanks in that time?
And how looks the filter of your first stage?

but also @axxel57 might have a point here.

I did a LoB (with steel tanks) at the beginning of December 2023 and I suspect that the tanks were full of rust as just after the LoB I serviced my 1st stage (Mk11) and fount its' interiors (including but not limited to the filter) covered by a very fine rust dust. Luckily the 1st stage parts haven't rusted (thanks to the lack of humidity and salt in the interiors I suppose) so they were cleaned easily. BTW, I also dive regularly with my own steel tanks - but I've never seen any rust inside them at vis (I fill them in in a reputable dive shop) hence it is unlikely (I hope) they are the source - unless there has been something very wrong in the shop's compressor recently.

It looks like that my C370 has been a victim of the combination of factors. First of all, the design flaw that Rober described, some extra rust "seasoning" from rusty gas (probably from that LoB's tanks), as well as me not cleaning/servicing it more often.

From now on, I will disasemble/clean them more regularly.

I have another C370 to be serviced soon (this one with much fewer dives and it hasn't been used to that LoB) and I will compare its interiors.

Robert I will try to record on video the assembly procedure, but I am afraid my bench and camera might not be ideal for this, hence I don't know how clear the details will be recorded. I will give it a try though.

Best regards

 

[axxel57]

Thanks Robert. Everything you say makes perfect sense.

but also @axxel57 might have a point here.

I did a LoB (with steel tanks) at the beginning of December 2023 and I suspect that the tanks were full of rust as just after the LoB I serviced my 1st stage (Mk11) and fount its' interiors (including but not limited to the filter) covered by a very fine rust dust. Luckily the 1st stage parts haven't rusted (thanks to the lack of humidity and salt in the interiors I suppose) so they were cleaned easily. BTW, I also dive regularly with my own steel tanks - but I've never seen any rust inside them at vis (I fill them in in a reputable dive shop) hence it is unlikely (I hope) they are the source - unless there has been something very wrong in the shop's compressor recently.

It looks like that my C370 has been a victim of the combination of factors. First of all, the design flaw that Rober described, some extra rust "seasoning" from rusty gas (probably from that LoB's tanks), as well as me not cleaning/servicing it more often.

From now on, I will disasemble/clean them more regularly.

I have another C370 to be serviced soon (this one with much fewer dives and it hasn't been used to that LoB) and I will compare its interiors.

Robert I will try to record on video the assembly procedure, but I am afraid my bench and camera might not be ideal for this, hence I don't know how clear the details will be recorded. I will give it a try though.

Best regards

I suspected rust in the tank as the culprit for this particular problem, because the plastic threads were covered with very fine rust and because it seemed to me it was much too much rust dust there.
Normally, if the metal parts are attacked by (salt) water (or dirt with rests of salt water), it "eats" parts of the metal and chrome and you find pits like the ones on the o-ring gland (rust from there would have been very little).
This metal part looks perfect after cleaning, the chrome is intact, so I still think that this particular very fine "rust dust" shown on the pics is more probable from a "contaminated" tank than from galvanic corosion of any kind.
I"m quite sure one finds rust dust particles also in other parts of the second stage like on the LP seat and in the LP hose.
My interpretation of the deposited rust on the o-ring is that it comes from that side as it comes to the plastic threads.
Not sure if I could explain clearly what I mean.....
So probably it"s correct what Stepfen writes, it"s a mix of factors.

 

[stepfen]

As an update, I disassembled a friend's C370 yesterday. This was bought new about 3 years ago, but have had much less dives (around 50 maybe) since then. From the look of it, my friend didn't rinse his regs very well after diving as I fount quite a bit of salt deposit in the case. Also, he hasn't been in the LoB I suspect had the rusty tanks/gas.

Here is how the sleeve looked like:

This sleeve is rusty too, and for some reason one side of it got most of it, but generally it is in much better condition. I haven't cleaned it yet, but from the look of it, it is just surface rust - no pits etc.
The adjustment shaft is pretty clean although it has a bit of rust deposited on it too.

Once more. Lesson learnt - disassemble/clean internals more often...

Cheers