since i started tec diving, i can comfortably say, this was the most debatable topic i had with multiple tec divers with different level of expertise's. my tec instructor uses AI and a redundent SPG. however when he goes below 90 meters he only trust SPG and removes AI as it is an addtional failure point "in his view". personaly i am more of an AI and tending to remove SPG as i had a good number of SPG failures over the years (not a fair comparison, as i used SPG for much longer). currently i am planning to remove the SPG and relying on AI only on my main reg and deco as well. these days i belive that AI has been long enough to gain reliability. and i love the fact that it calculates SAC, view all air supplies on my computer and later i can review the data and understand more my breathing patterns. so as an answer it depens on your risk assessment on either or both.
The curious case of AI. Do you use a back up SPG while using AI?
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OMyMyOHellYes
Contributor
Why do you prefer a button out of curiosity?
OP, not all transmitters are equal, I had a D4i with the suunto transmitter, it was bad and hard to check if the connection worked, had a few cases where it disconnected during the dive and didn’t reconnect.
I have used the Perdix ai transmitter and it never failed me in about 100+ dives I used it. I am back to SPGs because I don’t feel the next to plug the AI since I moved to CC (makes little difference to me but I’d have to buy more AI transmitters …)
mr_v
Contributor
Tanks (OC)
Buttons on sidemounted bailouts (I am on CC) because:
- I can see them easily.
- I don't like bending HP hoses.
- I can see valves, 1st stages in my config, so if there is an issue, like a leak, I'll see it.
- My primary bailout reg is under my chin - I'll notice any gas escaping right away.
- My secondary bailout is charged, off, and isolated - unless there is a tank valve rapture, gas won't leak.
Gauges on 9' hoses on any bottle that I will leave (e.g., stage or O2 deco). The hoses + gauges are flat against the tank - I do not bend them. I do this because it is easier to verify the pressure during the drop off or pick up. That way, I don't have to stand up or monkey around with the bottle.
Something like in the pic on the left, but the hose is 9'. The picture is borrowed from DGX:
Rebreather
I sold my transmitter. I did not want to have an additional failure point. Plus, despite diving CC, I still check my gas pressures frequently. Also continuous PPO2 monitoring is a good proxy for unintentional gas addition - if there is a dramatic change in PPO2, I know something is up.
Buttons on sidemounted bailouts (I am on CC) because:
- I can see them easily.
- I don't like bending HP hoses.
- I can see valves, 1st stages in my config, so if there is an issue, like a leak, I'll see it.
- My primary bailout reg is under my chin - I'll notice any gas escaping right away.
- My secondary bailout is charged, off, and isolated - unless there is a tank valve rapture, gas won't leak.
Gauges on 9' hoses on any bottle that I will leave (e.g., stage or O2 deco). The hoses + gauges are flat against the tank - I do not bend them. I do this because it is easier to verify the pressure during the drop off or pick up. That way, I don't have to stand up or monkey around with the bottle.
Something like in the pic on the left, but the hose is 9'. The picture is borrowed from DGX:
Rebreather
I sold my transmitter. I did not want to have an additional failure point. Plus, despite diving CC, I still check my gas pressures frequently. Also continuous PPO2 monitoring is a good proxy for unintentional gas addition - if there is a dramatic change in PPO2, I know something is up.
Bloody Marvelous
Contributor
You don't need an SPG if you have a transmitter, but it's a form of redundancy. Whether that redundancy is actually necessary, probably not. You don't have a redundant SPG for when your first one floods.
As long as you keep track of your battery charge, having only a transmitter is fine. Personally, I have both. I find an analog SPG is easier to understand than a digital readout, but having all the data in one screen is useful too. And a digital readout can't have a stuck needle. If it's not working, it won't display any information. A dive computer can also give you an audible or haptic alert to let you know it's time to switch gases, cylinders, or if you're running low on gas.
The argument of "failure points" is moot to me. Any redundant system introduces at least one additional failure point. If you're worried about failure points that much, you probably shouldn't be diving in the first place. It's a matter of setting off the likelihood of that o-ring blowing against a systemic failure. I don't think you need a backup inflator hose in case the first one fails, but a redundant buoyancy control system like a dual bladder wing or a drysuit may be worth considering. Two SPG's per cylinder may be overkill, but having an additional air source with its own SPG is good practice if you're diving in demanding conditions.
As long as you keep track of your battery charge, having only a transmitter is fine. Personally, I have both. I find an analog SPG is easier to understand than a digital readout, but having all the data in one screen is useful too. And a digital readout can't have a stuck needle. If it's not working, it won't display any information. A dive computer can also give you an audible or haptic alert to let you know it's time to switch gases, cylinders, or if you're running low on gas.
The argument of "failure points" is moot to me. Any redundant system introduces at least one additional failure point. If you're worried about failure points that much, you probably shouldn't be diving in the first place. It's a matter of setting off the likelihood of that o-ring blowing against a systemic failure. I don't think you need a backup inflator hose in case the first one fails, but a redundant buoyancy control system like a dual bladder wing or a drysuit may be worth considering. Two SPG's per cylinder may be overkill, but having an additional air source with its own SPG is good practice if you're diving in demanding conditions.
Happened to me a few weeks back on my last dive vacation. Since my Sunnto Pod was relatively newly purchased (only 48 dives and a year old) I didn’t anticipate it to run out of battery so quickly. But on my first dive day and some time before the first dive I found the the Air transmitter wouldn’t pair. Out of habit and decisions around redundancy I had an SPG anyways so it didn’t matter and I didn’t have to skip the days diving after spending $$$$ on the trip bookings.
Fortunately, the math of additional failure points doesn’t add up linearly in practice as both common sense and the above example illustrates. The likelihood and (very low) probability of both failing at the same time does…
Has anyone had a transmitter fail and start leaking gas? I’ve had them stop transmitting and flood but never lose gas.
I’m asking because if they don’t leak gas, then how are they any more of a failure point than a first stage port plug?
I’m asking because if they don’t leak gas, then how are they any more of a failure point than a first stage port plug?
Yes, there was a rash of swift transmitters with bad OPVs shortly after the swift came to market. It was a typical HP leak so not an emergency, but it did happen to many people.
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