[Dsg-mvt] APPARENTLY no isobutane anymore upstream of MFCs

[burkert]

Maxime,

  See if you can get the people together for a show and tell. I would be 
interested in attending.

Volker

On 1/10/18 10:18 AM, mdefurne wrote:
>
> Dear all,
>
> _*Before all explanations, I want to emphasize that Maxence and I are 
> not gas experts. So we are just explaining you what we did,why we 
> think it seems to be safe to make another test of the mixing system 
> with isobutane. We decline any responsability if something goes wrong 
> and final approval to start using mixing system with isobutane must 
> come from the JLab staff in charge of it. *_
>
> Last night with Maxence, we did the following procedure:
>
> - Closed all the valves.
>
> - Closed the manometer for the argon supply.
>
> From this state where everything is closed, we opened the valve in the 
> rack on the isobutane line supply and then filled the line from the 
> isobutane bottle to the upstream valve of MFCs with isobutane. The 
> pressure was about 25psi (cannot be more precise since the heat tape 
> was ON at 15% at that moment... when heat tape is warming, pressure is 
> increasing in the line).
> Then we closed the bottle and left the system in this state overnight, 
> i.e. all the line insulated with heat tape around at 15% filled with 
> isobutane.
>
> This morning we went to purge the line. To do so, we first open the 
> relief valve and then we open the one of the valves allowing to purge 
> with argon the isobutane MFC line. It is important to first open the 
> relief valve, otherwise isobutane will first flow in a line which is 
> not insulated and condense within a few seconds. (you tried it 
> yesterday evening and relief valve was then spitting liquid and gaz. 
> So 30F with no insulation will make isobutane condensing quite fast.)
>
> So this morning, only gaseous isobutane was exiting the relief valve. 
> Apparently it seems that isobutane is not condensing anymore. And once 
> the relief valve is closed, pressure in the line stayed at 0 (With 
> liquid in it, I would expect to have some pressure built in the line). 
> I nevertheless insist on the "apparently" since the relief valve is 
> not exactly on the isobutane line.
>
>   So, considering all this, I would _*only recommend*_ to start 
> testing the mixing system with isobutane again. But _*final approval 
> must be given either by a staff of JLab since this system is JLab 
> responsability.*_
>
> If you want a demonstration of the test later today (because the mail 
> might not be very clear without the rack in front of you), we can 
> organize it. However, I have not a faintest idea about what the next 
> test is to ensure that isobutane is gaseous, except going through one 
> MFC (no need to start using both immediately and risk to lose both of 
> them).
>
> Finally, 15% for the heat tape seems fine for ~30F. But temperature 
> will get colder over the week end and next week. We might consider to 
> run safe, i.e. testing again isobutane state as soon as we hit a new 
> minimum of temperature.
>
> Kind regards,
>
> Maxime
>

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