Eanx shaken and not stirred

[Splitlip]

Well I saw something new today, and maybe someone can splain it to me.

I went in to LDS this morning for a 34% fill. I decided to wait, have a donut and coffee. I am in no rush, no one else is in there so I tell the guy to take his time.

Well the guy that fills my tanks is pretty good in giving me the mix I ask for. Never more than a a tenth or 2 off. To his credit he takes pride in nailing the mix.

Well he finishes, I pull the tank from the bath, calibrate the analyzer to 20.8 and the tank comes up 32.5%. I tell him he blew this one. He says "wait, I'll fix it".

He takes the tank, lays it over and proceeds to roll it like a logger for several seconds.
Gives it back to me, I put the analyzer back on it comes up 34.1. I put the analyzer back on the calibration tank and it reads 20.9.

I finished my coffee and needless to say analyzed again thinking maybe it was a function of time between the fill and the analyzer. This is a partial blend facility.

Can somebody offer an explanation?

Thanks

 

[Wildcard]

What were you drinking in your coffee?

 

[freediver]

What were you drinking in your coffee?

heh

 

[el ridgeo]

Sunspots, phase of the moon, or possibly magic.

 

[spectrum]

The rolling of mixed gas cylinders was been discussed a lot perhaps a year ago. Try searching "rolling tanks". I forget what merit there was but it gets nasty when you do it to doubles.

Pete

 

[texdiveguy]

It's VOO-DOO!!!

Or just a case of a blender 'rolling' the cylinder to create a more 'homogenous' mix....it's more fun to think it VOO-DOO.....

The rate of the PP fill was probably very slow....in most cases a normal rate of fill will blend the EANx gases, though it does happen like you described on slower rates of fill.

 

[Wildcard]

Much like dice, roll em untill you get what you want....In the end it's just what you expected.

 

[miketsp]

..snip..

Can somebody offer an explanation?

Thanks

Sunspots, phase of the moon, or possibly magic.

This is a well discussed topic.
It's not a question of the gases "settling", it's simply that at 200 bar gases start to get viscous and diffusion velocities are slow so there is a slow spontaneous mixing time. Various posters ran calculations on this.
By rolling them you really do speed up the mixing (diffusion) process.

 

[Splitlip]

It's VOO-DOO!!!

Or just a case of a blender 'rolling' the cylinder to create a more 'homogenous' mix....it's more fun to think it VOO-DOO.....

The rate of the PP fill was probably very slow....in most cases a normal rate of fill will blend the EANx gases, though it does happen like you described on slower rates of fill.

Thanks. Thats what he said. The slower the fill, the greater the swing. He also commented, (now that I know I am not totally wacked I will bring it up), that the swing is greater for taller and slender tanks. I use the stubby 95 lp's.

 

[Splitlip]

What were you drinking in your coffee?

Yeah, I didn't hear that one yet this morning