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

[mdefurne]

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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