500 PSI is 500 PSI?

[Splitlip]

500 psi in my worthington hp's is ~ 14.5 CF
500 psi in an al 80 is ~13 CF
500 psi in an lp 95 is~ 18 CF

Dobled up, 2X

[CompuDude]

Originally Posted by h2odragon1

500 psi is not a unit of gas volume.
500 psi is a unit of time.
TIME TO SURFACE!!!

Just hope you're not at 130' with a mandatory deco stop ahead of you when this thought occurs... and your buddy doesn't go OOA... and there's no current on the way back to the exit!

[navyhmc]

Originally Posted by scubadiver888

In other words, how much air you should have at the end of a dive is a lot more complex than most Open Water Scuba Divers know. PADI believes this information is more information than they need to know. A lot of people on the 'other' board greatly disagree with this. I've met a lot more people who would never go diving if they had to learn this stuff.

When you're first starting out, I do believe that taking all the air management issues into account is a bit difficult and overwhelming. As a new diver, knowing that you need to be in the boat with 500pis or as a lot of resort chaters ask 800 psi is not too difficult to manage. There's just too much other stuff to think aobut first. With time, rock bottom gas management can be taught and used. But the KISS of 500/800 psi works within MOST recreational settings, more so if your using your head at all times. You have to start somewhere.

[scubadiver888]

Originally Posted by navyhmc

When you're first starting out, I do believe that taking all the air management issues into account is a bit difficult and overwhelming. As a new diver, knowing that you need to be in the boat with 500pis or as a lot of resort chaters ask 800 psi is not too difficult to manage. There's just too much other stuff to think aobut first. With time, rock bottom gas management can be taught and used. But the KISS of 500/800 psi works within MOST recreational settings, more so if your using your head at all times. You have to start somewhere.

Yes, I'm starting to see PADI's philosophy and realizing that with the right approach it can be a good thing.

When I become an instructor, I'm not going to teach Rock Bottom Gas Management right away BUT before my students graduate Open Water I will make sure they know there is more to gas management than 'back on the boat with 500 PSI'. When they are ready I'll teach them about it.

Basically, get them hooked then let them know there is more to know.

[redsoxphan]

All great info!! As I stated in another thread (tank sizing questions)...this is not something the average diver gives much thought to. They just "do as they're told/taught". I feel like I've learned more in 10 minutes reading this thread than I did during my entire OW class...to whom should I make my check out to??

Thanks for starting this thread rednose.

[IndyDiver]

Originally Posted by CompuDude

Just hope you're not at 130' with a mandatory deco stop ahead of you when this thought occurs... and your buddy doesn't go OOA... and there's no current on the way back to the exit!

I think you are confused about the purpose of a buddy, CD. A buddy is there in case you run out of air. There is no value in diving with someone who runs out of air themselves. Geeezz, that would be pointless.

...

[Tekdivr]

The truth of the matter is that how much air you should have left depends on the size of your cylinder and how much air you use per minute. Bigger cylinder means you can let the PSI go lower than a smaller cylinder. Higher Surface Air Consumption (SAC) rate means you need to reserve a higher PSI.


I don't totally agree with this statement. Granted the larger cylinder is going to carry a higher volume of gas, but 500 psi is 500 psi in regards to tank pressure and your regs ability to use it. Given variances in pressure gauges the 500 psi "on the surface" rule is a good one to follow. You start factoring in SAC rate and tank volume at those lower pressures and you may just come up empty before expecting it due to an inaccurate gauge reading. I usually plan for my safety stop to hit around 500 psi, that way if something were to go wrong, I'm 15' from the surface. Just a thought....

[rednose83]

Originally Posted by redsoxphan

Thanks for starting this thread rednose.

No problem. I think a lot of people don't learn (or think about) the why of what they're doing.

[Jack Hammer]

I know the question at hand is about volume differences, but it relates, so....

The 500psi "rule" isn't about keeping a specific volume of gas in a tank, it has do with with keeping a reasonable safety factor. Gauges are most accurate in the center of their range, the closer you get to empty, the less accurate the gauge becomes. From what I understand this was especially true in the past when gauges where less accurate than today. Dive operators don't want people running out of gas while diving or running a tank low enough for it to become difficult to breath off of or donate air from. There are enough people out there who would run a tank to the verge of empty thinking it's ok to do if there was no "requirement" to surface with a minimum reserve. 500 is a nice round number on the gauge, hence, the 500psi "rule."

[captain]

Originally Posted by Jack Hammer

Gauges are most accurate in the center of their range, the closer you get to empty, the less accurate the gauge becomes. From what I understand this was especially true in the past when gauges where less accurate than today.

Actually gauges in the past were problably more accurate. The smaller the range of a gauge the more accurately it can be read. Most all gauges today have a 0 to 5000 psi range but in the past most had a range of 0 to 3500 psi or 0 to 3000 psi.
For a 3000 psi tank the most accurate gauge would be a 0 to 3500 psi one and a 0 to 3000 psi one for a 2600 psi tank.