Shop drains tank before fill

[SubseaSports]

I went to Force-E a few days ago with 5 tanks, HP 120s, partially filled with nitrox anywhere between 34-37%. I asked if I could have them all filled to 32%. I was told that I would have to drain all the tanks if I wanted 32. I opted to just have them filled with 36%. All of them came out between 36.4-36.7%. So there are also edge cases when a shop might want to drain a tank.

It's been a while since I have had a tank filled at one of their locations....assuming they bank 36%.
32% as well? I recall my tanks taking a bath there.

Banking 36% makes more sense because you can obviously dilute with air to get 32 or whatever is lower. Eptying partially filled tanks that have richer mix to get a lower mix would get us chewed out lol. Dumping tanks means moving them, waiting, using more banked gas etc.
Equalize your hp 'like' filled tanks, pump to 2600~ with 36%, top off with air, collect money.

 

[SlugLife]

Shirley a tank filled in a water butt must cool down far more quickly than one in air?

I always figured that not overheating the tank its self and exploding reasons was the main reason, to use water.

Consider the possibility that the person filling your tank is a low-wage, disinterested, dive-shop employee who somehow managed to make it past the interview-stage but doesn't really or care about the safety concerns of diving. It's not that hard to splash a little bit of water onto the valve or the transfer-whip and not notice. That little bit of water gets into tanks here-or-there, and starts causing corrosion to a few dozen customer tanks, and those customers rightly get pissed off at the shop. It's probably easier to just make sure there's one less thing a dive-shop employee could screw up. There's also dealing with water on the floor, which could be a slipping hazard, or just creating muddy messes.

Having dealt with incompetent dive-shops, including incompetent VIP technicians, I'd probably prefer there was one less thing for them to screw up. That said, I'd probably have a water-bath at a personal fill station if I had one.

 

[MrChen]

It's been a while since I have had a tank filled at one of their locations....assuming they bank 36%.
32% as well? I recall my tanks taking a bath there.

Banking 36% makes more sense because you can obviously dilute with air to get 32 or whatever is lower. Eptying partially filled tanks that have richer mix to get a lower mix would get us chewed out lol. Dumping tanks means moving them, waiting, using more banked gas etc.
Equalize your hp 'like' filled tanks, pump to 2600~ with 36%, top off with air, collect money.

They said they bank 36%.

 

[Divin'Papaw]

Consider the possibility that the person filling your tank is a low-wage, disinterested, dive-shop employee who somehow managed to make it past the interview-stage but doesn't really or care about the safety concerns of diving. It's not that hard to splash a little bit of water onto the valve or the transfer-whip and not notice. That little bit of water gets into tanks here-or-there, and starts causing corrosion to a few dozen customer tanks, and those customers rightly get pissed off at the shop. It's probably easier to just make sure there's one less thing a dive-shop employee could screw up. There's also dealing with water on the floor, which could be a slipping hazard, or just creating muddy messes.

Having dealt with incompetent dive-shops, including incompetent VIP technicians, I'd probably prefer there was one less thing for them to screw up. That said, I'd probably have a water-bath at a personal fill station if I had one.

In experience (as opposed to a theoretical list of potential problems), I've never had an issue with water (and thus corrosion) getting into any of my tanks from being filled in water baths. The shops I know that use this practice have a pretty consistent, thorough process they follow to prevent this. Keep in mind that they are also filling their own steel tanks ... a lot. You can certainly come up with a number of potential issues. I've not had an issue firsthand over the past 7 years of using shops that do this regularly. My tanks have always passed VIP with flying colors, no tumbling or whipping required.

 

[MrChen]

Scuba Works also bathes the tanks, they come out cold to the touch.

 

[mdwalter]

I have never been able to observe this, not ever!
... drain basically as fast as possible, tons of condensation on the OUTSIDE, tanks are fully wet, dripping in “sweat” from condensation, but INSIDE is always bone dry, ...

... never seen condensation inside.

Yes, of course, because there is basically no moisture inside the tank to condense.

 

[mdwalter]

Doesn't fast draining freeze the valve and damage O-rings?

No

 

[mdwalter]

I see this effect is more pronounced in smaller tanks, which seems counterintuitive. When partial pressure filling 2/3L rebreather bottles with trimix, analyzing it right after fill, you get a reading with the bottle standing up, flip it upside down and you’ll get a wildly different reading. Not so much with larger cylinders like doubles.

That's different, since the He has a drastically different density than the O2 and air or 32 you top off with. Mix takes a while to homogenize; nitrox, not so much.

 

[mdwalter]

are these damaged

View attachment 790559

Hard to tell from the photo, but probably not.

 

[mdwalter]

Consider the possibility that the person filling your tank is a low-wage, disinterested, dive-shop employee who somehow managed to make it past the interview-stage but doesn't really or care about the safety concerns of diving. It's not that hard to splash a little bit of water onto the valve or the transfer-whip and not notice. That little bit of water gets into tanks here-or-there, and starts causing corrosion to a few dozen customer tanks, and those customers rightly get pissed off at the shop. It's probably easier to just make sure there's one less thing a dive-shop employee could screw up. There's also dealing with water on the floor, which could be a slipping hazard, or just creating muddy messes.

Having dealt with incompetent dive-shops, including incompetent VIP technicians, I'd probably prefer there was one less thing for them to screw up. That said, I'd probably have a water-bath at a personal fill station if I had one.

Oh, and you were making so much sense... right up until that last sentence.