Bad scuba advice you've received

[b1gcountry]

Mechanical gauge accuracy is not as precise as you think. Check out the info at the bottom of DGX page:

Pressure Gauges (SPG)

Submersible Pressure Gauges (SPGs) and Instrument Consoles

www.divegearexpress.com

TL;DR mechanical gauges are not as accurate close to empty and full - the most accurate reading will be in the middle. This is not a defect but a side effect of the mechanism used.

That's an article. I asked if anyone had seen this happen in real life.

I haven't. All my gauges are pretty close to each other. I got bored and checked once.

It's like a gas tank. It only really matters that you can predict when it's empty.

 

[Saboteur]

go diving in Koh Tao.

What’s bad about Koh Tao? I’ve never been there.

 

[jeffmg]

That's an article. I asked if anyone had seen this happen in real life.

I haven't. All my gauges are pretty close to each other. I got bored and checked once.

It's like a gas tank. It only really matters that you can predict when it's empty.

Anecdotally, I partial pressure fill my own tanks for nitrox.
For a 3500psi tank I’m usually adding around 400-450psi of o2 to a cylinder with around 500psi left in it
The needle on my whip gauge changes at a different rate than my spg if it’s hooked up and usually ends at a different pressure
That’s especially true if I dump a tank and fill with o2 from 0

I will say it’s more on the conservative side
The needle on the spg tends to stay at 0 until a couple hundred psi are in the tank, sp you may have a little more than 500psi when it ready 500 psi

 

[BoundForElsewhere]

What’s bad about Koh Tao? I’ve never been there.

Total tourist trap. Too many snorkelers and new students. Like in the 100's everywhere. Reef is in shock.

 

[passeparici]

Total tourist trap. Too many snorkelers and new students. Like in the 100's everywhere. Reef is in shock.

Koh Tao is not that bad... It might be crowded sometime (true with many sites nowadays) but you still have nice dive sites. Snorkelers are not really present in most of the sites. It is a convenient island to scuba dive, every thing is made for that and if you happen to be in vacation around Koh Tao it is nice to have a few dives. For me the real problem comes from the fact that the operators are reluctant to bring the divers to the best sites because those are farther (that could be the reason we think it is overcrowded...) : choose your operator accordingly !

 

[BoundForElsewhere]

Koh Tao is not that bad... It might be crowded sometime (true with many sites nowadays) but you still have nice dive sites. Snorkelers are not really present in most of the sites. It is a convenient island to scuba dive, every thing is made for that and if you happen to be in vacation around Koh Tao it is nice to have a few dives. For me the real problem comes from the fact that the operators are reluctant to bring the divers to the best sites because those are farther (that could be the reason we think it is overcrowded...) : choose your operator accordingly !

I dove with Master Divers and they were awesome. We only went out to Chumphon and Southwest once.

Maybe I've been spoiled with elsewhere.

 

[SlugLife]

re: Tank pressure discussion.
If your tank pressure gets too low, there can be some risk of water intrusion or condensation. As some people pointed out analog-gauges, tend to lose accuracy at low PSI too. The biggest problem is mostly the idea of a beginner-diver, with cheap inaccurate equipment, pushing limits.

One local shop will refuse to fill tanks that are low, without getting a fresh VIP. I don't know their exact cut-off PSI, but reading between the lines I suspect it's around 300psi. Regardless, I do have a transfill-whip and could bring up the pressure if needed, and a VIP cert, so I could always just empty it and put on a fresh visual sticker. But that doesn't apply to everyone.

Personally, I don't have any big concerns with breathing down a tank lower than 500, because I have redundant air (pony bottle, or 2nd tank).

 

[boulderjohn]

One local shop will refuse to fill tanks that are low, without getting a fresh VIP.

I think this is BS. They get to charge you for a VIP you don't need. Ask them to explain the physics of it.

 

[crofrog]

I think this is BS. They get to charge you for a VIP you don't need. Ask them to explain the physics of it.

These tactics are so common in dive shops that aren't that busy.

 

[SlugLife]

I think this is BS. They get to charge you for a VIP you don't need. Ask them to explain the physics of it.

Actually, that fits into the theme of this thread:

About 2 years ago, the shop was very reluctant to fill my buddy's dive-tank that was low, around 200psi. We were able to "convince" them after a little arguing, but it did leave a bad taste in my mouth.

More recently I got my VIP certification. Just to be on good terms with the shop, I explained I had just received my VIP cert, just VIPed the tank, and that's why the tank was empty. The owner was okay with that (as he should be) but then said "you know why we won't fill empty tanks, they should have covered that in your class.." I didn't want to argue and figured, maybe I had missed something, so I didn't really say anything.

I asked my instructor, and he quickly responded that no such requirement exists.

The best I can think of, is that an empty tank may suggest a diver screwing around with their own equipment, and you might want to double-check that the valve is secure or that no debris is in the tank before filling for safety reasons. However, that wasn't anything my instructor mentioned.

Personally, I have a couple more reasons to be annoyed at this dive-shop, but unfortunately I don't really have other practical options for fills at the moment. And I get the vibe that if I did try to argue with him, he might refuse my VIP stickers, and there are probably better hills to die on.