40 replies to this topic

[Tolly]

Heh, I don't have enough experience yet to give up anything...except the snorkel...I did give that up...

[6Gill]

Well the whole be on the boat with 500psi is pretty weak seeing as 500psi equates do different amounts of gas left depending on tank size,rated pressure and configeration

[JimG]

Well the whole be on the boat with 500psi is pretty weak seeing as 500psi equates do different amounts of gas left depending on tank size,rated pressure and configeration

I agree with you based on math / physics, but the reason for that recommendation has nothing to do with the tank and everything to do with the gauge. Bourdon tube gauges (like the type used in SPGs) tend to be most accurate in the range represented by 25%-75% of full scale (that's between 1000-3000 PSI for a 4000 PSI gauge, and 1250-3750 PSI for a 5000 PSI gauge). The last few hundred PSI in either direction are the least accurate, so a gauge reading that's below 500 PSI could be off by a wide margin (which could spell dire consequences for you if it is reading "high").

Of course, if you are in the habit of periodically checking your gauge's calibration and have a pretty good idea of how "off" it is, then that would allow you to have a better estimate of how much gas you have left at the end of a dive. Most divers don't do that though, so the "500 PSI" rule is used instead. It's a nice round number that seems to provide an adequate enough margin for error..

[jextract]

Those interested in a good discussion of an alternative to that 500 psi rule should read this:
http://www.direxplor...ock-bottom.html

[captsteve]

The snorkel....

[6Gill]

Of course, if you are in the habit of periodically checking your gauge's calibration and have a pretty good idea of how "off" it is, then that would allow you to have a better estimate of how much gas you have left at the end of a dive. Most divers don't do that though, so the "500 PSI" rule is used instead. It's a nice round number that seems to provide an adequate enough margin for error..

Hi JIm,
People don't calibrate their SPGs Actually I'm not picky about all my SPGs(deco gases,but I check them just cause) but my back gas SPG is regularly checked.I also regularly service my SPGs,but then again I'll check a new tape measure againts a known standard,you be suprised how inacurate some tape measures are.

[ScubaDadMiami]

What do you do to service your SPGs (other than clean the threads, change the spool o-ring, etc.)? Do you do something to inside the unit?

[Walter]

I'll check a new tape measure againts a known standard,you be suprised how inacurate some tape measures are.

Do you toss your lead weights on a scale? Talk about inaccurate. Geeze!

[JimG]

People don't calibrate their SPGs.

That's because most modern SPGs can't be calibrated. They are effectively "throwaways". I have a few older brass gauges that can still be taken apart and serviced. I just recently threw out an old Sherwood Selpac gauge that had been cleaned and serviced several times over the years. I tossed it because the needle mechanism got permanently stuck after it flooded in salt water.

And to answer ScubaDad's question - the only service that I know of on modern SPGs is just what you described (clean the threads and spool, and lubricate or replace O-rings as necessary). They can also be checked against a high quality oil-filled gauge for accuracy.

I'll check a new tape measure againts a known standard,you be suprised how inacurate some tape measures are.

That explains what happened on the last home improvement project that I attempted.

[secretsea18]

Those interested in a good discussion of an alternative to that 500 psi rule should read this:
http://www.direxplor...ock-bottom.html

Oh yes, the 500psi rule.... I use two gauges, one normal spg and then one in my Vytec. They are quite close to each other.

I figure I will bring back air to the boat when they start reimbursing me for unused air!

Of course, It is important to not completely empty the tank or air, as a little water may seep in.

Robin

(strobe lights all around)

PS Also the snorkel has no place on your mask during a dive, unless you used it in your mouth. It belongs in your pocket. I take mine apart and it lives in my pocket.

Edited by secretsea18, 26 October 2006 - 06:02 AM.

[Walter]

That having been said, as far as I know every training organization requires both instructors and students to wear a snorkel during training. Now, I'm only a small Training Assistant moving slowly but surely through Master to DM status, but I wonder why the agencies make it such a fetish. Perhaps the more experienced folks can help me out here.

Most training organizations require snorkels, not all. The exceptions, of which I'm aware, are those that teach cave and cavern.

Liability. If agency A allows you to dive without a snorkel and you drown, your heirs might win a suit claiming you would have lived had their standards required you to have a snorkel.

[PerroneFord]

Hmmm,

Interesting question. Let's see some things I've let go since my initial training.


1. Snorkel
2. The idea of being back on the boat with 500psi
3. The idea that I would be hurt if I exceeded the table limits
4. The idea that a diving buddy was somehow a safe bet against diving accidents
5. The concept of a safety stop
6. The idea that overhead diving is dangerous
7. The idea of ascending vertically, hand above head, turning 360
8. The idea of descending vertically, feet down
9. The concept of venting my BC by pulling on the corrugated hose
10. The concept that I needed a tank banger or another noisemaker to get my buddy's attention.
11. The idea of donating the "octopus"
12. MOF = Distressed diver
13. The idea that "ocean diving is real diving and other diving is not"
14. The idea that there is "nothing to see" below 130ft
15. The idea that the Dive Master was necessarily a highly experienced and highly skilled diver.
16. The idea that number of dives somehow equated to skill or quality of diver
17. CESA

There's probably more, but these came to me off the top of my head.

[ScubaDadMiami]

Oh, how about this one: always exhale when the regulator is out of your mouth.

[PerroneFord]

I had to demo reg removal and recovery in a recent OW class and forgot this little gem. Instructor dinged me for it. I just laughed.

Rules for the sake of having rules drives me nuts.