[Dsg-rich] Follow up to RICH N2 flow loss last night

[Marco Mirazita]

Hi Tyler,
thank you for this update and for your intervention.
I have a couple of comments though.
1) Bob says that the N2 valve was off. What does it mean? That someone 
manually closed it?
2) From your analysis, we know that the valve was closed on June 3rd, 
then the backup system came into operation  and worked for 3 days, but 
we got an alarm only when also the backup system died. It means the N2 
system worked for three days in an unsafe mode without any warning. We 
got an alarm only when it was "too late" and the flow dropped to zero.
Fortunately, you, Bob and the jlab crew fixed the problem quickly and 
most likely the aerogel didn't suffer any damage, but for the future I 
think the alarm should be sent out when the primary system fails, while 
the backup must ensure enough time time to fix the problem.
Best regards,
Marco


Il 2019-06-07 14:17 Tyler Lemon ha scritto:
> Hello,
> 
>  In follow-up to last night's findings of RICH N2 supply having been
> shut off, attached are plots showing N2 panel pressures and N2 flow
> and N2 Volume humidity.
> 
>  From the plots of the N2 panel pressure and flow, it seems that
> something happened with the N2 supply maybe on Monday June 3. From
> June 3 to last night (June 6), there were three drops in pressure at
> the N2 panel:
> 
>  	* June 3 at 13:50 - Initial drop in pressure. It seems like the main
> N2 supply was shut off for some reason and the backup supply kicked in
> to keep N2 flow to RICH.
> 	* June 4 at 24:29 - Second drop in N2 panel pressure. This is
> probably the first 12-cylinder N2 backup bank running out and then the
> switch to the second 12-cylinder N2 backup bank. This swap is done
> "automatically" by having the first bank's regulator set higher than
> the second bank's.
> 	* June 6 at 15:33 - Third drop in N2 panel pressure and loss of N2
> flow. Second N2 backup bank ran out.
> 
> If the drops on June 4 and 6 are the N2 banks running out, it means
> the backup N2 banks will provide ~40 slm to RICH for ~ 3 days.
> 
> When Bob found the N2 was valved off and reopened it, the N2 flow,
> main N2 supply pressure, and overall N2 panel pressure returned to
> normal while the N2 backup supply pressure remained at 0 psi. This is
> because both N2 backup banks are now empty. We will have to get
> replacement banks for the future.
> 
> The second attached plot is N2 volume humidity values. Humidity in
> RICH only went up when N2 flow dropped to zero. Humidity in RICH
> increased ~ 1 % Relative Humidity during this period. At the time of
> this plot, the humidity values have almost returned to normal.
> 
> In summary, N2 flow last night was lost because the main Hall B N2
> supply to RICH was shut off for some reason and the backup system
> provided N2 to RICH for ~3 days before running out, dropping N2 flow
> to 0 slm. N2 Volume Humidity went up ~1 % RH during this time and has
> since returned to normal. The "positive" result of this event is that
> the N2 backup banks work correctly and can supply N2 to RICH for ~3
> days when the main Hall B N2 supply is lost.
> 
> Best regards,
> Tyler
> 
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