Pressure gauge reliability

[Bennno]

I've run the thought experiment of carrying two with manifolded doubles, one on each post. I'm a little surprised that's never done.

Lots of people used to do that before DIR got popular with the 'general population'.

 

[KeithG]

My mechanical spg finally failed. Well it showed symptoms of future failure. Water in the display and rust.

So I replaced it. $35 for 25 years service.

 

[rmssetc]

After a lively debate about whether the SPG will be replaced by a Wireless Air Integrated computers, I am curious how many people have actually experienced failures of either type of gauge. Feel free to post your tales of terror, and keep in mind that this is not scientific and does not necessarily contradict your blind faith in your preferred technology.

The poll may need to have another category:

[ ] Experienced WAI computer failure (flooded, fell off, inaccurate, etc)
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in this case, the transducer is working fine, but the display of the pressure reading is inaccurate or unavailable. By analogy, a trasducer failure is like a clogged (or burst) HP hose to an SPG...the signal isn't getting to the display. A computer failure is more like an SPG with the needle stuck at a high point...as the pressure drops the signal (pressure) is getting there, but the display is incorrect.

A temporary loss of transducer signal with a WAI computer doesn't necessarily affect the dive overall -- in fact, it may be so brief that the diver is unaware until they check the computer's log. I've got a dive in the Chac Mool cenote where the log shows a max depth of ~179'...pretty impressive for a cavern that's got a floor at ~45'.

 

[doctormike]

I've run the thought experiment of carrying two with manifolded doubles, one on each post. I'm a little surprised that's never done.

I think that you are suggesting that as an SPG redundancy strategy, not as a way of measuring tank pressure if you have to shut down a post. That is, in case the SPG fails, you would have another one. As has been pointed out, if you have to shut down a post, you exit immediately, so having an SPG on the remaining tank isn't important.

There are some pieces of equipment that are commonly duplicated for redundancy in technical diving - gas and a way to breath it, a mask, depth/time measurement, an SMB, lights in a cave, etc... The SPG is not one of those things. If your mask or your primary reg fails, you may not be able to make a safe ascent without a backup. If your SPG fails, you can, since you planned for enough gas to satisfy whatever deco requirements you incurred.

 

[2airishuman]

It doesn't provide any benefit.

unnecessary on doubles and can complicate things. Even in a cave, if a failure occurs, you just exit.

I think that you are suggesting that as an SPG redundancy strategy, not as a way of measuring tank pressure if you have to shut down a post. That is, in case the SPG fails, you would have another one. As has been pointed out, if you have to shut down a post, you exit immediately, so having an SPG on the remaining tank isn't important.

The benefit of having a second SPG is not that it allows you to continue a dive in the event of a failure. The benefit is that you can determine when one of the SPGs has failed in a fashion that causes it to falsely indicate more gas than is actually present, because in that case, the two instruments will not agree.

 

[doctormike]

The benefit of having a second SPG is not that it allows you to continue a dive in the event of a failure. The benefit is that you can determine when one of the SPGs has failed in a fashion that causes it to falsely indicate more gas than is actually present, because in that case, the two instruments will not agree.

Aha! Then you better have three so that you can use voting logic...

 

[PfcAJ]

The benefit of having a second SPG is not that it allows you to continue a dive in the event of a failure. The benefit is that you can determine when one of the SPGs has failed in a fashion that causes it to falsely indicate more gas than is actually present, because in that case, the two instruments will not agree.

Negative.

If you have a failure that requires you to shut down a post, the dive is over. You don't "continue a dive" with broke gear.

The failure you just describe is again not helped by two SPGs. Is one thats broken reading higher or lower? You have no way of knowing that in the water. Ergo, the dive is over. Issues with a gauge reading high (or low) are identified before you get in the water during predive checks, and then SPG is monitored throughout the dive based on what you expect the value to be and what is displayed. The SPG should be a confirmation of what you think the value gas will be (especially in a technical context). If you're surprised at what the SPG says, something isn't right. Head home and sort it out on the surface where being wrong doesn't matter.

All you've really done by adding a 2nd SPG is doubling your risk (however slight) of SPG failure.

 

[doctormike]

All you've really done by adding a 2nd SPG is doubling your risk (however slight) of SPG failure.

And entanglement, since it will most likely be on the side of the long hose, and the canister light cable if you are using one...

 

[WarrenZ]

I had to chuck one after 10 years it got water in it and I had white "stuff" in the gauge face not sure when it was going to fail but I didnt want to find out so it got replaced.

 

[AJ]

I've run the thought experiment of carrying two with manifolded doubles, one on each post. I'm a little surprised that's never done.

I understand your way of thinking, put let's ask ourselves something else: is a failing SPG a potential hazard? If you say 'yes', you might want to have two gauges (wether it will be SPG or/and AI). If you don't consider an SPG necessary for getting home safe, why bother with a more complex setup? GUE/DIR supports the second line of thought. Personally I believe you should do whatever you like, but make sure you don't add complexity that is hard to manage or in the worst case gives conflicting information. The cure might be worse than the solution.

OT: My personal experience with Suunto AI is not good. For the first 30 or so dives all went fine. After that it became unreliable, Finally it stopped working during a diving vacation in the Red Sea. Inspection later on turned out the housing was leaking, leading to a short cut. A new tranmitter would have cost me around € 250,-. As I had an SPG already as backup, it became my primary gauge. I must admit I considered AI handy at the time, but it was too costly for me to replace. Now I'am used to my SPG and feel no further need for AI. I have had no problems with my SPG yet.