[Dsg-mvt] Liquid isobutane between bottle and MFCs

[mdefurne]

Hello everyone,

We are currently flushing the lines and testing all MFCs with Argon, 
except the brand new Isobutane MFC on Mix2.
We opened all valves upstream of the MFCs to have Argon. We changed the 
fraction of Mixture 1 from 90-10-10 to 40-30-30 in order to use equally 
all MFCs. For Mix 2, we set isobutane to 0 and close the upstream valve 
off because we want to protect it.

So far , Mix1 isobutane MFC provided a good stable flow of Argon. Now we 
will decrease it to try to find the leak flow.

Also, before opening doing this flushing/testing of all MFCs and lines 
with Argon, we tried to purge the isobutane pipe between the bottle and 
the MFCs... A lot of fluid got out of it!!!! Once we thought that the 
purge was done, we closed the relief valve and then the pressure in the 
pipe kept increasing even if the isobutane bottle was closed... most 
likely due to remaining liquid isobutane turning into vapor in the pipe 
again.

We should first try to ensure to have no condensation in this part. Test 
is easy and MFC-safe. Just close all valves off upstream of MFCs, close 
the argon pipe and open isobutane one. Then purge the isobutane line and 
see if you have drops out of the relief valve. You have first to clean 
the isobutane pipe. We did this cycle several time whereas the bottle 
was closed and there were still pressure building up in the line.

I haven t checked the heat tape settings on this one. Maybe it is still 
a few percents. It might need to be increased. But let s wait for 
tomorrow, once all lines and tanks are flushed with Argon down to the 
detectors.

Maxime

PS: Who did just switch mode from default to purge? (Around 4pm). It was 
done like this on purpose. In purge mode, isobutane MFC is turned off.  
(And apparently not leaking since flow reads -5.4 sccm... which is good 
news!). But apparently, in purge mode, CF4 MFCs keep running.