Spg backup to transmitter

[Rayk]

Wait, what? I don't agree with that at all.

Assuming that you can see your button gague (i.e. sidemount), if your transmitter fails, you are now diving with an SPG. Are SPGs no longer an acceptable way of monitoring tank pressure? Or are you saying that button SPGs are not good enough? I don't that data, but they have less failure points than a standard SPG (no hose or swivel).

I mean, I understand why people find WAI convenient, but it's not like it's no longer safe to dive without it.

In my back mounted doubles, I have analog SPG on the left post and transmitter on the right, i like it because it makes easier specially if I have stages. I take a sneak peak to SPG when I assemble the tanks to be sure it’s working and carry on with transmitter during the dive. In that case I would definitely keep doing my dive if my transmitter fails.

In sidemount, I don’t dive with gauges and transmitters combined, I only have transmitters and if one of them fails (which never happened before), depending on when and where I will probably end the dive.

Another thing to consider, not all dives are same, not all conditions are same. If we are talking mixed gas, staged decompression dive it is another story, if I am doing recreational dive with my buddy who has almost same SAC rate and consumption with me, that’s another story.

There is more than one way to skin a cat.

 

[doctormike]

My comment about "all agreeing" was based off of grant and rayK saying they would turn the dive if penetration was involved.

I could edit it but I'll let it stand.

OK, but I'm interested, and always happy to learn! That's what I like about this place. Not trolling.

It seems like a number of people said that if they had a visible button SPG and a transmitter on any give gas source, and if the transmitter failed, the dive should be thumbed.

So I can only see two possible interpretations of that:

1) It's not safe to dive without a backup to your tank pressure monitoring.

2) A button SPG is not adequate for tank pressure monitoring

Both of those are arguments that could be made, and I'm interested in those arguments. I - like many - used to dive for years with a set of manifolded doubles and a single SPG, but maybe that's no longer considered an appropriate configuration?

 

[L13]

My comment about "all agreeing" was based off of grant and rayK saying they would turn the dive if penetration was involved.

I could edit it but I'll let it stand.

Not all dives involve penetration. And even for penetration, I don't think it is an open and shut case. If an regular SPG is good enough, a Button in side mount should be good enough. The addition of a non-working transmitter is not significantly more of a risk than a plug in the same HP outlet. Yes, if I was diving at the edge of my comfort zone I would turn turn the dive on a transmitter failure, but otherwise why?

Of course, just a transmitter has fewer loss of gas failure points than a button SPG, which has fewer loss of gas failure points than a regular SPG. So eliminating both types of SPG does eliminate loss of gas failure points. But, a Button + Transmitter still has less loss of gas failure points than a regular SPG on a short hose, and ADDS redundant pressure indication.

 

[doctormike]

In my back mounted doubles, I have analog SPG on the right post and transmitter on the right, i like it because of make it easier specially if have stages. I take a sneak peak of SPG when I assemble the tanks to be sure it’s working and carry on with transmitter during the dive. In that case I would definitely keep doing my dive if my transmitter fails.

In sidemount, I don’t dive with gauges and transmitters combined, I only have transmitters and if one of them fails (which never happened before), depending on when and where I will probably end the dive.

Right, but that wasn't the question. The question was about thumbing the dive if you had a transmitter AND an SPG on each tank. Of course you would thumb a dive if you lost your only tank pressure monitor.

 

[L13]

OK, but I'm interested, and always happy to learn! That's what I like about this place. Not trolling.

It seems like a number of people said that if they had a visible button SPG and a transmitter on any give gas source, and if the transmitter failed, the dive should be thumbed.

So I can only see two possible interpretations of that:

1) It's not safe to dive without a backup to your tank pressure monitoring.

2) A button SPG is not adequate for tank pressure monitoring

Both of those are arguments that could be made, and I'm interested in those arguments. I - like many - used to dive for years with a set of manifolded doubles and a single SPG, but maybe that's no longer considered an appropriate configuration?

I don't think they are arguing 1). They are advocating the removal of the backup since it can't be used.

 

[doctormike]

Of course, just a transmitter has fewer loss of gas failure points than a button SPG, which has fewer loss of gas failure points than a regular SPG. So eliminating both types of SPG does eliminate loss of gas failure points. But, a Button + Transmitter still has less loss of gas failure points than a regular SPG on a short hose, and ADDS redundant pressure indication.

I think that the main issue with failure points on any tank pressure measuring device is the loss of data, not the loss of gas, since it's an HP port.

If you have a full AL80 and cut the LP hose, it drains in 83 seconds. If you cut the HP hose, it takes 22 minutes.

 

[grantctobin]

Right, but that wasn't the question. The question was about thumbing the dive if you had a transmitter AND an SPG on each tank. Of course you would thumb a dive if you lost your only tank pressure monitor.

Less accurate, inability to discern the difference between e.g 2000 and 2400, and anecdotally have had more of them break (pin at full, pin at empty, etc) than a standard gauge. I’d also assert that the majority of people with sidemounted cylinders properly mounted can’t pull their cylinder forward to a point where they could see the button. Do what one wants in open water, but I don’t trust button gauges much more than a empty notfull full, and if you lose an SPG on an open circuit penetration dive primary bottle, you thumb it.

 

[doctormike]

I don't think they are arguing 1). They are advocating the removal of the backup since it can't be used.

So they are saying that a button gauge isn't acceptable?

 

[doctormike]

Less accurate, inability to discern the difference between e.g 2000 and 2400, and anecdotally have had more of them break (pin at full, pin at empty, etc) than a standard gauge. I’d also assert that the majority of people with sidemounted cylinders properly mounted can’t pull their cylinder forward to a point where they could see the button. Do what one wants in open water, but I don’t trust button gauges much more than a empty notfull full, and if you lose an SPG on an open circuit penetration dive primary bottle, you thumb it.

OK, that makes more sense. Buttton gagues are not accurate enough to be used during a dive. So then if you want a backup to your transmitter, then why not a regular SPG on a 6" hose?

And if you use that, would you agree that it would be adequate to execute a dive without a transmitter?

 

[grantctobin]

OK, that makes more sense. Buttton gagues are not accurate enough to be used during a dive. So then if you want a backup to your transmitter, then why not a regular SPG on a 6" hose?

And if you use that, would you agree that it would be adequate to execute a dive without a transmitter?

I don’t believe in the need for a backup to a transmitter (or a backup to an SPG). The parts required to add another backup (splitter, hose, swivel, SPG) is another four o-rings, the two on the swivel of which cause an annoyance and have a higher failure rate than a transmitter. To quote your post, you and I have happily dived for decade(s) safely with only one form of pressure monitoring on a set of doubles. The SPG or transmitter are “already” the backup to your gas calculations and planning. There shouldn’t be more than a couple hundred psi swing in either direction relative to what you’re expecting.

Full disclosure, I did use button SPGs on my back mounted CCR as a start of dive (full/not full)