Shop drains tank before fill

[Wibble]

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

 

[VikingDives]

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

I don't know about that, but it certainly damages hearing.

I have a piece of PVC pipe filled with steel wool inside, that has a lpi attachment on it. Both problems solved.

 

[broncobowsher]

That reminded me they mentioned something about the O2 pressure. I think they use a single large O2 bottle or small bank they don't have a pressure booster on their O2 supply. I would guess the cost of using extra O2 from a cylinder is less than the cost of a pressure booster system.

Correct. I see this in shops that do minimal nitrox fills. A cascade of 4-6 bottles of O2. When the lowest bottle in the cascade is only 300 PSI, you need an empty tank to get that little bit of gas moved over. So the next bottle in the cascade doesn't drop as much. You waste a bit of O2, but O2 is fairly cheap. And boosters are expensive. It can make sense to save money on a booster that gets little use and that can more than pay for the lost O2. Less so if leasing cylinders, more so if doing owner exchange and the gas supplier is nearby.

 

[johndiver999]

I have never been able to observe this, not ever!
I‘vê worked for shops that perform over 1500 visuals a year, tanks are put outside (because of the noise) to 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, this observation was performed from immediately after draining to hours after draining, not ever have I seen it cause condensation INSIDE a cylinder, steel or aluminum.

Short of an explosion, burst disk failure will drain tanks as fast as it can be drained, I’ve been around a few of those, generally you’d take the opportunity to perform a visual in those cylinders given they‘ve been drained, again, never seen condensation inside.

Do you roll the cylinders after fills to mix up the oxygen with the air?

 

[rjack321]

I have never been able to observe this, not ever!
I‘vê worked for shops that perform over 1500 visuals a year, tanks are put outside (because of the noise) to 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, this observation was performed from immediately after draining to hours after draining, not ever have I seen it cause condensation INSIDE a cylinder, steel or aluminum.

Short of an explosion, burst disk failure will drain tanks as fast as it can be drained, I’ve been around a few of those, generally you’d take the opportunity to perform a visual in those cylinders given they‘ve been drained, again, never seen condensation inside.

That's because scuba air has a dew point somewhere around -60F/-50C assuming the filters on the filling compressor are in good condition. Cylinders dont get that cold unless you're draining them outside at McMurdo station.

"Condensation" forming inside is a myth, or it was a poor quality fill you're draining.

 

[MrChen]

We had a popular dive shop which did this, and I hated it. I hear they don't do it anymore, but after years of hearing hissing tanks, I've found other places to get my fills.

 

[Pavao]

Do you roll the cylinders after fills to mix up the oxygen with the air?

You’ve lost me man. How did we go from condensation inside from fast draining to rolling cylinders after fill?

 

[Divin'Papaw]

I recently moved and am using a new shop to get fills. The partial pressure blend for Nitrox. Somehow in the discussion about the mix I wanted they revealed that they drain the tank before filling. They start with the O2 then add the air to get the mix. They reasoned that the O2 mixes better that way. Most shops I know that partial pressure blend use a calculator to find the amount of O2 and air to add to achieve the desired mix then add the O2 and top with air. Just wondering if that could be allowing humid air into my tank and cause problems at vis time.

Get your tanks filled at one of the 5 Force-Es in SEFL before you head back home. That’s what I typically do. I’m in & out in 30-45 min. Thankfully I also have a shop in Naples that banks 36% as well for the occasions I need to get fills back here.

 

[NitroxSam]

My LDS has been doing this for years . After the fill they are rolled. They also fill the tanks in a big tank of cold water.

 

[Bob DBF]

My LDS has been doing this for years . After the fill they are rolled. They also fill the tanks in a big tank of cold water.

There is something to be said for tradition, I'll look through Churchill's quotes and get back to you.