Consensus on Overfilling Tanks?

[rob.mwpropane]

I know FL cave country is pretty notorious for overfilling....lets face it, I think they're the cowboys and the outlaws of the US. I mean, it is FL after all.

In all seriousness though, what is acceptable to overfill a tank to? I'm not really looking to overfill my tanks, but I'd like to have them be at what they're supposed to be when they're cooled off which requires at least a little overfill at first. Some places around here are not willing to do so (or at least I haven't asked). So I end up with ~3200 or so in my 3442's.

Is the reason shops won't over fill due to the liability? I know one shop that fills mine to ~ 3700 or 3800?, so they're really nice when cooled. Should I be asking for this? Is there a law or something that prevents this?

I know hydro is 5/3 working pressure, so I'm assuming it's 5737 in my 3442's. In my tiny scuba brain 3800 psi for a few min won't hurt anything compared to that.

What do you get your tanks filled to? What's the acceptable overfill in cave country? I know what's on paper, but I know there are slight differences in the real world.

Thanks! Hope everyone is staying safe!

 

[decompression]

A good slow fill will hit the full mark without much loss after cooling. A good filler can hit the full mark with just a few PSI over after cooling. If you have time it makes sense for a slow fill.
Further, 200-300 PSI don’t really matter due to SPG inaccuracies and temp drop when it hits the water.
In short, don’t over fill, calc rock bottom gas and enjoy your dive.

 

[kelemvor]

Acceptable overfill depends on the tank. Most shops fill my LP (2400) steels between 3400 and 3600 cold.

Most shops fill my al80's to 3200 cold.

I suspect most of the shops are setup to fill to whatever cools off to 3200, and they aren't really setup to fill a higher pressure tank like your 3442.

I don't own any steels that aren't rated for LP

 

[kammel78]

Is the reason shops won't over fill due to the liability?

Liability and in quite a few instances ignorance.

 

[rob.mwpropane]

Liability and in quite a few instances ignorance.

You mean ignorance on being dumb enough to overfill, or ignorance in not knowing that it's really not a big deal?

 

[kammel78]

You mean ignorance on being dumb enough to overfill, or ignorance in not knowing that it's really not a big deal?

Ignorance and being dumb are two different things. Ignorance is not an insult, you don't know what you don't know.

I'd say the majority of people involved in diving, including divers, are ignorant of the science behind most of the "rules", including dive shop owners filling tanks. Overfilling tanks is not dumb, it's just an increase in risk. If you're okay with that level of increased risk, then by all means, overfill. Everything we do involves some level of risk. IMO, "dumb" is somewhere the risk is high, say shooting yourself in the head, not something with relatively low risk, like overfilling a scuba tank.

 

[rob.mwpropane]

A good slow fill will hit the full mark without much loss after cooling. A good filler can hit the full mark with just a few PSI over after cooling. If you have time it makes sense for a slow fill.
Further, 200-300 PSI don’t really matter due to SPG inaccuracies and temp drop when it hits the water.
In short, don’t over fill, calc rock bottom gas and enjoy your dive.

"If you have time"...what kind of time? I was at the shop filling 2 tanks for 25 min yesterday. They didn't do it in water, but they were pretty warm when done. I can't imagine being stuck there on a summer day for longer, especially if there was a few people doing the same.

 

[rob.mwpropane]

Ignorance and being dumb are two different things. Ignorance is not an insult, you don't know what you don't know.

I'd say the majority of people involved in diving, including divers, are ignorant of the science behind most of the "rules", including dive shop owners filling tanks. Overfilling tanks is not dumb, it's just an increase in risk. If you're okay with that level of increased risk, then by all means, overfill. Everything we do involves some level of risk. IMO, "dumb" is somewhere the risk is high, say shooting yourself in the head, not something with relatively low risk, like overfilling a scuba tank.

Ok, I understand. Some people use the word ignorance as a synonym for dumb or lacking intelligence. I know it's not supposed to be, but it is. Thanks for the clarification.

I'm sure tanks are engineered with a huge margin for error, over engineered. I can't imagine that filling a tank a few 100 psi is anymore risky then filling to the recommended psi. I'm not an engineer, I don't own a compressor, and I don't know where the line in the sand is. Just talking and gaining some knowledge.

 

[kelemvor]

Some of the better shops will just ask you what you want in the tank.

 

[kammel78]

I'm sure tanks are engineered with a huge margin for error, over engineered. I can't imagine that filling a tank a few 100 psi is anymore risky then filling to the recommended psi. I'm not an engineer, I don't own a compressor, and I don't know where the line in the sand is. Just talking and gaining some knowledge.

Like Jay pointed out, gauge inaccuracies means 200-300 psi differences are quite common and as you pointed out scuba hydros are 5/3 overpressurized every 5 years and the hydro measures the expansion of the metal to make sure it's within an acceptable range. Also, there's a big difference in steel and aluminum tanks, what I consider okay to overpressurize a steel tank to, I'd never do for an aluminum tank.