Shop drains tank before fill

[inquis]

Some shops in Cave Country will fill tanks without even unloading from the truck. I put them in the water trough because it makes enough difference to me.

 

[Pavao]

That’s from my arrival to departure. That includes unload, fill, test, load. Fill time if half that or less. The cold water bath absolutely makes a difference.

I think there’s some exaggerations and downplays with your numbers, but fine, I’ll go with them for the sake of discussion…

Taking your lower number (20 min) and accepting the long unload, test, load times, leaves 10 minutes for fill, that is still more than twice the needed safe time to fill 2600 psi. But it’s not even 2600psi, according to you, they reach 3600-3800 after they warm up. What do you mean by that, btw?
And btw, a steel with 1000psi filed to 4000 will result in a 3600 fill after cooling, and it’d only take 5 minutes to do it

When I’m in cave country, where most shops, not all, still uses water bath, I never use them, I still get my desired pressures, and they match any of my buddies who use the water bath…

 

[BlueTrin]

Probably end up with a hot tank that cools to a much lower pressure. Then have to moan at them to top it off.

Bit surprising they do this though as they will need to run their compressor for a lot longer. Sure, sometimes it's unavoidable if their oxygen pressure is low. Mostly they won't do this -- or certainly not in my experience.

Some shops find it hard to top up and get an accurate %.

I know Vobster (in the U.K.) prefers to empty to do Nitrox (didn’t go there for the last year though)

 

[BlueTrin]

Can someone explain to me, the reason for tank rolling like this?

Is it because not patient enough? To let it mix?
Unless there is a ball brg like a paint can, I don't see how rolling works.

I have seen it work, like @rjack321 said, I was dubious too and a non-believer

Analysed it, not happy, the guy rolled it a bit and tank was re-analysed and it matched what was required.

 

[Gone for diving]

I have seen it work, like @rjack321 said, I was dubious too and a non-believer

Analysed it, not happy, the guy rolled it a bit and tank was re-analysed and it matched what was required.

The heat layer make some sense to me,,,

I wonder if you keep rolling of you can get whatever reading you want..

 

[BlueTrin]

The heat layer make some sense to me,,,

I wonder if you keep rolling of you can get whatever reading you want..

Nah you just need to slow down the flow when it approaches the value you want (seen some people do that)

 

[Pavao]

The heat layer make some sense to me,,,

I wonder if you keep rolling of you can get whatever reading you want..

Too time consuming, much quicker to just dial the analyzer to the desired mix

 

[DirtFish]

I worked in a very large urban fire department which had 4 fire stations designated as filling stations. Each had large modern OSHA approved filling rooms capable of filling 5 SCBA bottles at a time, with a circulating water bath to keep everything cool. These were pretty much fully automated so even a firemonkey could do it. During large fires those filling stations would be filling 100 tanks a night.

 

[MrChen]

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.

 

[Tracy]

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.

Most shops that bank nitrox do it for a reason.
It speeds up filling and increases accuracy.
If they have air, 32, and 36, they would have to blend air and 32 to get your 34-37% down to 32. That takes time and time costs money. It is much cheaper and easier to dump your tanks and fill them back with 32%.