HOG SPG (BAR) Labelling Error?

[WhiteSands]

How do you figure that could pose a safety problem?

I believe there is a safety issue when a diver is mislead into thinking they have more air then they actually do.

When you're down one mark from 50, you think you have 40 bars. In reality, you only have 37.5 bars.
When you're down two marks from 50, you think you have 30 bars. Actual fact you only have 25 bars.
Down three marks, you think you have 20 bars. You have in fact only 12.5 bars.

Most recreational diving is done at around 18m depths. Recreational divers mostly start to surface when they hit 50 bars.

Should an issue happen during this time, e.g. SMB line gets tangled, diver drops a camera, diver suddenly sees a whale shark swim by during safety stop and thinks he has enough air to take a look, he may think he has more time to deal with the issue than he actually has.

When the fuel gauge reads empty, the car may still be running.

Unless I am mistaken, I don't think so. When the gauge hits 0 there is no pressure left in the line. Which means the tank will be completely empty.

It bothers me because I have been using this SPG for close to a year without actually even noticing the difference in graduations. I always thought it was wonky or inaccurate down from 50 bars but never realized why.

 

[redacted]

I believe there is a safety issue when a diver is mislead into thinking they have more air then they actually do.

When you're down one mark from 50, you think you have 40 bars. In reality, you only have 37.5 bars.
When you're down two marks from 50, you think you have 30 bars. Actual fact you only have 25 bars.
Down three marks, you think you have 20 bars. You have in fact only 12.5 bars.

Most recreational diving is done at around 18m depths. Recreational divers mostly start to surface when they hit 50 bars.

Should an issue happen during this time, e.g. SMB line gets tangled, diver drops a camera, diver suddenly sees a whale shark swim by during safety stop and thinks he has enough air to take a look, he may think he has more time to deal with the issue than he actually has.



Unless I am mistaken, I don't think so. When the gauge hits 0 there is no pressure left in the line. Which means the tank will be completely empty.

It bothers me because I have been using this SPG for close to a year without actually even noticing the difference in graduations. I always thought it was wonky or inaccurate down from 50 bars but never realized why.

As other posters have suggested, the value of each increment is constant. What is really happening is the gauge is pegged at a value greater then zero. So, when your HOG SPG hits one mark below 50, you have 40 bar remaining (and should be firmly focused on finishing your dive). At 10 bar (hopefully after you are out of the water, the needle will hit the peg and move no more; but you may well still have gas remaining. So, no safety issue unless you are seeing such reading UW. And then, the safety issue is your's and not the gauge's. If one misinterprets the marks, one would think he has less gas than he actually has; ignoring other possible gauge accuracy problems.

I have found it to be a good idea to breath my rigs all the way down to empty (in a controlled environment) so I know how my regs and SPG will perform in such a situation. I had some interesting results.

 

[WhiteSands]

As other posters have suggested, the value of each increment is constant. What is really happening is the gauge is pegged at a value greater then zero. So, when your HOG SPG hits one mark below 50, you have 40 bar remaining (and should be firmly focused on finishing your dive). At 10 bar (hopefully after you are out of the water, the needle will hit the peg and move no more; but you may well still have gas remaining. So, no safety issue unless you are seeing such reading UW. And then, the safety issue is your's and not the gauge's. If one misinterprets the marks, one would think he has less gas than he actually has; ignoring other possible gauge accuracy problems.

I have found it to be a good idea to breath my rigs all the way down to empty (in a controlled environment) so I know how my regs and SPG will perform in such a situation. I had some interesting results.

I see.

If that is the way it works then I guess it is a non-issue. I will test it out on a near-empty tank on my next dive.

 

[dfx]

I recall reading that SPGs (both analogue and digital) shouldn't be trusted that much on the lower end of the scale, i.e. below 50 bar. Meaning that if you're on that "2 lines below 50 and 2 lines above zero" line, it could be 20, 25, 30, or anything else around those numbers and you really shouldn't be in the water any more.

 

[John_B]

I have found it to be a good idea to breath my rigs all the way down to empty (in a controlled environment) so I know how my regs and SPG will perform in such a situation. I had some interesting results.

This. The first thing I do with a new SPG is breathe a tank all the way down, just so I know where "all the way down" will actually be if I were to ever need it. I also like to know if 3000 psi on the gauge is anywhere near 3000 psi.

Interesting video clip that shows what a brass/glass SPG looks like behind the label for those who haven't seen it: [video=youtube;gs-4dta_w-Y]http://www.youtube.com/watch?v=gs-4dta_w-Y[/video]

 

[lowviz]

I see.

If that is the way it works then I guess it is a non-issue. I will test it out on a near-empty tank on my next dive.

Might want to be careful with that. If you breathe a tank all the way down underwater AND THEN DESCEND A BIT you may risk getting water into your cylinder. I don't know for sure, but seems likely.

Reg guys: any input on this???

---------- Post added May 16th, 2014 at 02:58 AM ----------

...//...
When you're down one mark from 50, you think you have 40 bars. In reality, you only have 37.5 bars.
When you're down two marks from 50, you think you have 30 bars. Actual fact you only have 25 bars.
Down three marks, you think you have 20 bars. You have in fact only 12.5 bars. ...//...

Unless I am mistaken, I don't think so. When the gauge hits 0 there is no pressure left in the line. ...//...

Not exactly. Think of 10 Bar as the new "Zero". That mark on the gauge IS mislabeled, it really should read: "Anything between 0 and 10 Bar".

Each gradation is 10 bar. The needle can't drop below 10 Bar due to the pin. So they just relable it to be "0". Any small errors are now in your favor, BUT YOU CAN'T COUNT ON ZERO AS BEING 10 BAR.

Let's assume that they gave you all the graduations and your gage was reading zero. Now, if your gauge is off 5% high you may think that you always had that one last breath left. Pegging the needle at 10 Bar eliminates this problem by making everybody's "stamp out and ship" inexpensive SPG's all roll off the assembly line reading zero without any expensive fussing or zeroing.

It really isn't any big thing...

 

[WhiteSands]

Thanks for the clarification.

 

[alpertu]

Is it because of the first stage of regs IP is set to around 8-10 bars?? You can read on some BCD inflators manuals that power inflate button will not work if the tank pressure below 10 bars.

 

[victorzamora]

Not realy, you can suck air out of a tank down to literally nothing because your second stage will still work. As has been mentioned before, it's because the cost and difficulty with getting a 300bar gauge to show 0bar accurately are both dramatically high. So instead, they just show "empty" at 20bar or so.

Having said that, all gauges are most accurate at closest to the range they're calibrated at. For example, if you calibrate your Nitrox Analyzer with air and measure EAN32, you're good to go. If you calibrate it with air and measure Pure O2....you could be several percentage points off. If you calibrate it with Pure O2, you can measure EAN80 very accurately. Scales meant to weigh trucks aren't accurate weighing people. The list goes on and on. Regardless, at 20-30 bar.....the amount of air you have in your tank shouldn't matter, you need to be going up as fast as practicable.

 

[alpertu]

..the amount of air you have in your tank shouldn't matter, you need to be going up as fast as practicable.


Thats the part that we agree. But still i didn't understand the reason.. What is the exact reason for less marked between 50 to 0 Bars than the other parts of spg? does it wanted to be more accurate?