Consensus on Overfilling Tanks?

[RyanT]

@rob.mwpropane, I haven't really timed it, but my preferred shop probably takes at least 45 minutes to dry fill my tanks. Even with that they are a little warm when full (nothing like a quick fill though). And yes, my non-cave country shop overfills my tanks.

 

[tbone1004]

Hydro on your 3442's is 5250psi, the ratio is 3/2 for the high pressure exemption permits.

Getting underfills is a function of ignorant fill stations. The service pressure is called out specifically as at room temperature *can't remember what the actual temperature is*, so if the tank is warmer than that, it is allowed to be at a higher pressure so it cools to the right pressure. Most dive shops don't understand this, so they just set the regulator to working pressure and call it a day.

In most shops in cave country, the regulators are set at 4000psi which is the hydro pressure of 2400psi 3aa low pressure bottles. They end up cooling to about 3600psi regardless of what you're filling. 2250psi steels will get stopped around 3000psi to cool to 2800 ish, and Al tanks will usually go to 3300 or so and cool to 3000. There are specifics to each fill station except for Amigos where you get to fill anywhere up to 4000psi, but that's roughly correct.

 

[W W Meixner]

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!

Rob...

Hoping you and your family are well too...

You do not have to overfill initially to have the cylinder cool to identified working pressure...fill to identified working pressure...let cylinder cool...top off to identified working pressure...

Standard industry practice/liability/safety of fill staff...

You shouldn't have to be in a hurry when you fill your cylinders...a little prior planning will work wonders...

Forget about re-hydro pressures...forget about what Florida cave divers do...as neither are relevant when it comes to the practice of intentionally overfilling cylinders...

W...

 

[tbone1004]

@W W Meixner try telling that to fill stations who are trying to make money. That is not a practical way to fill as it doubles the labor cost associated with filling. I have not seen that as SoP for any filling station, regardless of commercial gas cylinders, SCBA cylinders, or scuba tanks. The only exception to that I have ever seen is when PP filling custom trimix blends.

 

[Johnoly]

Ok, ... Just talking and gaining some knowledge.

If you need more gas......
Why can't you just buy bigger tanks ??

 

[rob.mwpropane]

The service pressure is called out specifically as at room temperature *can't remember what the actual temperature is*, so if the tank is warmer than that, it is allowed to be at a higher pressure so it cools to the right pressure. Most dive shops don't understand this, so they just set the regulator to working pressure and call it a day.

That's a pretty interesting point that I hadn't (and probably would not have) thought of.

I'm so glad this place (SB) exists.

Rob...

Hoping you and your family are well too...

You do not have to overfill initially to have the cylinder cool to identified working pressure...fill to identified working pressure...let cylinder cool...top off to identified working pressure...

Standard industry practice/liability/safety of fill staff...

You shouldn't have to be in a hurry when you fill your cylinders...a little prior planning will work wonders...

Forget about re-hydro pressures...forget about what Florida cave divers do...

W...

If we lived in a perfect world, sure. If the dive shop was closer, if there wasn't a line to wait, if..... but in the real world there will be times when this doesn't work. I have 2 places that fill within 30 minutes of my house (both are special trips). Then there's 3 others within an hour drive (also special trips). I don't especially like people as a whole, so I'd like to get in and get out and be on my way to do other stuff than just hang around. Truth be told, only one shop is worth talking to. Sadly he's 1.25 hrs away, and one toll.

 

[tbone1004]

@rob.mwpropane sounds like you need a compressor...

 

[wetb4igetinthewater]

I make the effort to go back and get my tanks topped off after being filled. This is the only way I've been able to get around rated pressure.

 

[rob.mwpropane]

@rob.mwpropane sounds like you need a compressor...

I also need a winning lottery ticket, a better 401k, a rebreather, and while your at it I think a vacation house down in FL somewhere.

Oh....don't forget, more certs so I can do more types of diving!

Edit: Or I need FRIENDS with compressors!

 

[rob.mwpropane]

I make the effort to go back and get my tanks topped off after being filled. This is the only way I've been able to get around rated pressure.

The only place I seem to be able to have the time to do that is Dutch Springs. Drop the tank off, go eat or something, and come back.