Wireless

[Rainer]

Looks like we're in total agreement!

 

[dtkachev]

My questions were all answered, but for some reason you're having trouble with what I think is really simple logic concerning the probabilities of independent operations. It doesn't matter that having two SPGs doubles the chance of ONE failing (add the probabilities). The point is that the chance of having a problem (which is NO spg) goes down signiticantly (multiply the probabilities). Given all the other responses, however, this just isn't important...

I absolutely agree with the statistical reasoning that you provide if you are looking at SPG failure: yes you decrease the probability of not being able to have a correct reading, as you will have a second one that will provide a correct reading, hence chances of not being able to have a correct reading go down with an increase in the amount of SPG's. The only thing you forget to add into the system, is the fact that by adding a second SPG you are increasing the probability of failure in the O-ring on the first stage, hence you are increasing the chances of having gas loss.

Here is what the statistical outcome of adding second spg:
1. Decrease the chances of not being able to have a correct reading with regards to the amount of gas in your tanks (gas pressure, to be correct) by a factor of two.
2. Increase the chances of having a failure in the o-ring on the first stage by two. As you are adding another o-ring, by adding hose (transmitter from the original question).

What was said in the two points above is statistically significant, what will be said below is subjective: In my opinion it is better to have an spg failure, rather than a HP leak on your first stage. For spg failure you still have a bottom timer, plus your buddy's spg (assuming that you know yours and your buddys breathing rates). Whereas with two spg's the chances of having a failure in the o-ring, hence the chances of having a problem with gas loss are doubled. That is why I believe it is not worth having a second spg.

 

[Scared Silly]

I agree with you but at the certain point when question is answered and explained I really see no reason for additional explanations when everything is clear.

Clear to whom?? Just because you might have seen the light does not mean others have or will be able to see it so easily. I do applied research in my job. I can not begin to count the number of times I have explained multiple times some idea to my colleagues. They are not dumb people - just seeing things differently. When this happens it means I probably was not clear and I try to explain it differently. Sometimes the shoe is on the other foot and I am the one asking alot of questions.

Yes, sometimes it seems like you are beating the subject to death. But obviously the OP still was not seeing things from the DIR perspective.

BTW this is what makes a good teacher. Some one who not only understands the material but can present it in multiple ways so that it can be understood by a number of different people.

 

[do it easy]

The critical part here is that SPGs are not like flashlights- if a flashlight fails, you deploy another- the more the merrier. If an SPG fails (bubble bubble, uh oh, trouble!) then you've got gas management issues to deal with.

 

[texdiveguy]

The critical part here is that SPGs are not like flashlights- if a flashlight fails, you deploy another- the more the merrier. If an SPG fails (bubble bubble, uh oh, trouble!) then you've got gas management issues to deal with.

I had an SPG failure once this year....luckly I was in 35ffw on a rec. dive in a local quarry and it was a minor air leak.......completed the dive aware of the situation and monitoring it,,,,replaced the 2 small o-rings on the spool during the SI and the SPG was good to go.

 

[do it easy]

I had an SPG failure too- same deal with the 003 o-rings, but mine was on my AL40 O2 bottle. Lucky for me, it was after the dive and the bottle was just sitting at the water's edge. If it happened during the dive, the bottle probably would have been empty in about 10 minutes.

 

[texdiveguy]

I had an SPG failure too- same deal with the 003 o-rings, but mine was on my AL40 O2 bottle. Lucky for me, it was after the dive and the bottle was just sitting at the water's edge. If it happened during the dive, the bottle probably would have been empty in about 10 minutes.

I hear you....I was real lucky I think....it just dribbled 'air' ever so slow. I started diving in 71' not having an SPG, guess I could do it again...NOT.

 

[DIR-Atlanta]

2. Increase the chances of having a failure in the o-ring on the first stage by two. As you are adding another o-ring, by adding hose (transmitter from the original question).

As somebody else pointed out, there will always be an O-ring at the first stage, even if the port is plugged. So you do not increase the number of first stage O-rings by adding an extra hose or transmitter.

The place where you do increase the O-rings is at the SPG itself. There are two small O-rings on the "spool" that connects the SPG to the hose. This is a mechanical connection, and one that is very prone to leakage (as texdiveguy learned on his quarry dive). The good news is that HP leaks are not typically catastrophic, as the rate of leakage is usually pretty slow. It's probably not a good idea to continue a dive if you discover one, but on the other hand it's not going to be as urgent a situation as a leak in a LP hose.

The biggest downside to adding extra gauges (mechanical or otherwise) is that they do not really give you any additional "good" information that you can't get elsewhere. That in effect makes them unnecessary. And of course, if it's not really necessary, then there's no reason to bring it on the dive.

 

[darkpup]

As somebody else pointed out, there will always be an O-ring at the first stage, even if the port is plugged. So you do not increase the number of first stage O-rings by adding an extra hose or transmitter.

I agree with you on the number of o-rings in the system neither increasing or decreasing with the transmitter, but having an extra knob sticking off your first stage that can either be damaged from impacts or unscrewed by physical contact is an additional failure that a simple nut will not encounter.

Something to consider.

~ Jason

 

[DIR-Atlanta]

I agree with you on the number of o-rings in the system neither increasing or decreasing with the transmitter, but having an extra knob sticking off your first stage that can either be damaged from impacts or unscrewed by physical contact is an additional failure that a simple nut will not encounter.

That's actually a separate issue from the number of O-rings. I agree that adding equipment in this way increases the chances of physical damage, entanglement, etc.