Oxygen clean MH8A transmitters (Shearwater compatible) with different transmit intervals

[taimen]

I would like to use two transmitters with my Perdix AI, one for 100% oxygen and another for a lean mix. (Oxygen and diluent...)

Shearwater says their branded transmitters are not suitable for >40% oxygen. The Aqualung is the only one I can see advertised as oxygen clean. Aqualung is also less expensive.
I already have one Aqualung branded MH8A transmitter with a green cap (sold as oxygen clean) that has been used with everything my tanks have seen, so it is not clean anymore.
Is it possible to oxygen service a used transmitter?

Using two transmitters may cause interference problems, if those transmitters have the same transmit interval. This is why Shearwater sells grey and yellow transmitters. Shearwater manual hints that color coded transmitters from other manufacturers may have different transmit intervals too, but I haven't been able to find any specifications regarding this.

Thus what I think I need is one oxygen clean MH8A and another one with a different transmit interval that doesn't have to be oxygen clean. Do green and black capped Aqualungs have different intervals and is it possible (or absolutely needed) to oxygen service a used transmitter?
Or can I find another oxygen clean transmitter somewhere which doesn't interfere with my green capped Aqualung?

 

[KenGordon]

Get a scope and an appropriately short bit of wire, watch the transmitters do their thing and see what the chances of a clash are. I am guessing you’d need to be pretty unlucky. TDMA underwater, hmmm.

Do you really care how much gas you have on the dive? You typically start with plenty and unless you have a leak or a bad day buoyancy wise you know how much the dive will take. If you run out you bail out.

I suppose you might be using your dil as bailout...

 

[taimen]

Do you really care how much gas you have on the dive? You typically start with plenty and unless you have a leak or a bad day buoyancy wise you know how much the dive will take. If you run out you bail out.

I suppose you might be using your dil as bailout...

Nope, just recently started learning to dive a JJ with a DSV.
This was recommended by my instructor as an easier way to check pressures. The SPG configuration in the JJ is not really a convenient one. I already have the Perdix AI which I use as secondary anyway.
I can see this whole idea is opening a whole can of worms, but with my very limited experience I will trust my instructor and try it. At least it will give me one more blinking warning if I end up diving with my oxygen valve closed or running out of oxygen.

I hope we can keep this thread discussing transmitter related issues, instead of going into DSV/BOV debate or general wireless AI trashing. If you want to add something related to those issues, I really do appreciate if you PM me or start another thread.

 

[stuartv]

There are green, yellow and grey transmitters. It is my understanding that the grey ones have a 5 second interval and the green and yellow are something like 7 and 8 seconds. Not sure if I'm remembering the exact numbers correctly, but I believe it's something like that.

That said, I have used 2 grey ones side by side and never had any issues. If they did somehow get on the exact same interval and start acting squirrely, all you have to do is shut down one tank and purge it to blow off the pressure in the tank. That will cause the transmitter to turn off. Then turn the tank back on, so the transmitter turns back on. The chances of it turning on and being on the exact same interval again seem EXTREMELY low.

I don't really know about O2 cleaning any of them. I do have the same plan as you and was figuring I would buy a green transmitter for my rEvo sometime soon.

 

[RainPilot]

I’ve never had a transmission clash in around 300 dives in SM with 2 grey transmitters

 

[taimen]

I found a manual online with the following comment:

So Shearwater branded transmitters are rated compatible only up to 40% Oxygen, Oceanic sells only oxygen compatible and Aqualung has separate <40% and O2 clean models. Confusing, and this data is not easy to find online. And the difference may be only o ring material...

 

[Aquanomad]

Thanks for finding that info. I need an o2 one for my breather. Oceanic sells black, green, and yellow. Do you know if the yellow and green are both good for o2?

 

[jgttrey]

My guess - and it is PURELY a guess -- is that there is no difference between how the "nitrox ready" transmitter and the "O2" transmitter are prepped and it is just a liability thing.

The Shearwater O2 disclaimer in its FAQ is nearly word for word the same as the DGX disclaimer about O2 service for stuff it sells -- same lawyers or they cribbed off one another. Since there is no real legal standard for that vis a vis scuba, some in industry just don't want to make the representation. Both sort of imply that it should be okay, hypothetically, they just don't want to be held responsible. I understand that. No criticism implied.

Again, that's just a guess so don't rely on my speculation.

I wonder about the internals of that pressure sensor and whether you could just flush with a Blue Gold solution and a syringe or whether there is something exposed that wouldn't like it. Not that I'm going to try, but I'd be interested in someone who knows what is inside that little hole has to say about whether that could be done.

 

[stuartv]

My guess - and it is PURELY a guess -- is that there is no difference between how the "nitrox ready" transmitter and the "O2" transmitter are prepped and it is just a liability thing.

The Shearwater O2 disclaimer in its FAQ is nearly word for word the same as the DGX disclaimer about O2 service for stuff it sells -- same lawyers or they cribbed off one another. Since there is no real legal standard for that vis a vis scuba, some in industry just don't want to make the representation. Both sort of imply that it should be okay, hypothetically, they just don't want to be held responsible. I understand that. No criticism implied.

Again, that's just a guess so don't rely on my speculation.

I wonder about the internals of that pressure sensor and whether you could just flush with a Blue Gold solution and a syringe or whether there is something exposed that wouldn't like it. Not that I'm going to try, but I'd be interested in someone who knows what is inside that little hole has to say about whether that could be done.

Not that I'm going to try it on mine, but it seems like if it can contain 3500 psi of gas, putting some liquid cleaner in it probably won't penetrate to anything that it could damage.

 

[dmaziuk]

The issue is whether the cleaner could react with the materials.