SPG or AI, Who’s Right?

[Bob DBF]

Yes the glass/plastic face on modern spgs are not meant to burst hence the relief plug I would just hold the spg face towards you and the rear pointed towards the ground

The face on old SPG's were not meant to burst either. I hold it away with the edge, strongest part towards me. The initial problem of the SPG face going ballistic is due to the diver opening the tank valve too fast, slower and the SPG would just break and leak.



Bob

 

[dead dog]

A man with one watch knows what time it is. A man with two watches is never sure.

And...a broken watch tells the correct time twice a day.

 

[Littlerayray]

The face on old SPG's were not meant to burst either. I hold it away with the edge, strongest part towards me. The initial problem of the SPG face going ballistic is due to the diver opening the tank valve too fast, slower and the SPG would just break and leak.



Bob

All in trying to say is it's an out of date practice just like turning your valve a 1/4 turn back is an old out of date practice
The reason for the 1/4 turn was cuz the valves would freeze jam open if opened all the way hence the 1/4 turn back

 

[Bob DBF]

All in trying to say is it's an out of date practice just like turning your valve a 1/4 turn back is an old out of date practice
The reason for the 1/4 turn was cuz the valves would freeze jam open if opened all the way hence the 1/4 turn back

These "out of date" practices were only instituted to cut out the time it takes to teach people how their gear works and how to take care of it. I like to call it training by catchphrase.

Case in point, 1/4 turn back derives from the fact that most valves are not made to seat when open so should not left in that condition. A very slight movement of the valve is all that is nessary, not a 1/4 turn. The issue is not so much that it would freeze open, as there are other valves in other uses that might, as someone might think it is stuck and cause damage by trying to force it open. Personally I don't care what others do, unless it is my gear.

On the SPG, I'm more interested in being safe when handling HP gas so I don't really want any of it near or pointing at my face until I know it handles pressure. When there were SPG face problems divers didn't get hurt because they used basic safety practices, not because of the "face the SPG away from you" catchphrase, which happened a decade later or more, when that issue was already solved.


Bob

 

[Paul M]

On topic - I trust the accuracy of my Perdix AI a little over my brass and glass spg but they are very close.

On the tangent topic - I watched most of these videos from Alec a couple years ago before taking certification courses. Imagine me, tongue almost bleeding, while our instructor tells us to turn the knob back a 1/4 turn and also point the spg plastic/glass away from our faces when opening the valve.

 

[wKkaY]

The service center I use is really professional and gives me a report after servicing. At 200 bars, my SPG reads 205 while the Perdix transmitter reads 196.

 

[Neilwood]

The service center I use is really professional and gives me a report after servicing. At 200 bars, my SPG reads 205 while the Perdix transmitter reads 196.

View attachment 458365

That is assuming the pressure gauge they are using is perfectly calibrated and accurate of course.

 

[Sam Miller III]

The exploding SPG face dates back to the introduction of the American made Mar-Mac SPG in 1954.

The problem was solved with the introduction of the Sportsways SPG a few years later with its modern technology and manufacturing techniques.

Exploding SPG faces should be extremely rare in modern diving- but the practice of turning the face down or away from the diver should remain as a common practice.

Who don't some of you late model tube suckers ask your fuzzy faced instructors " Why the SPG face should be turned away when the air is turned on?" I suspect the answers will astound you.

SDM

 

[stuartv]

My new Perdix AI indicates 200 Bar. The SPG tells 210 Bar. How to know who’s right?

Whichever one reads lower.

All in trying to say is it's an out of date practice just like turning your valve a 1/4 turn back is an old out of date practice
The reason for the 1/4 turn was cuz the valves would freeze jam open if opened all the way hence the 1/4 turn back

That's not why I do it.

I turn back just a little bit so that if I or anyone else checks it, it will move a little bit before it stops. The alternative of being open to the stop means that if someone grabs it and tries to turn it to open it and, because it won't turn, they think it's stuck and turn it even harder (which just doesn't seem good for the long-term health of the valve).

 

[Scared Silly]

Why don't some of you late model tube suckers ask your fuzzy faced instructors " Why the SPG face should be turned away when the air is turned on?" I suspect the answers will astound you.

SDM

Sam, given that yer a classic model damn near 99% of those on da board are late model tube suckers.