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So, how did this occur? Let us look at how the control system
currently works.<br>
<br>
The N2 flow is set at 500 cc/min at the MFC. The pressure protection
solenoids are controlled by a process controller. The process
controller receives a 4-20ma signal from the magnahelic pressure
transducer. Pressure setpoints are chosen for the process controller
when the solenoid valves should open and close. The return solenoid
valve position currently has no effect because the outlet valve is
closed. The gas supply solenoid valve opens and closes normally
according to the setpoints. <br>
<br>
This setup works fine as long as the detector is in place or the
supply and return lines are connected together. Once you remove the
detector and isolate the lines, you now have a problem. The control
system now has an input pressure signal that opens the supply
solenoid valve and flows gas at 500 cc/min, which will continue
until the input pressure signal increases to the setpoint that turns
off the supply solenoid. The transducer measures the pressure at the
exhaust bubbler. The bubbler is at atmospheric pressure and below
the setpoint required to close the solenoid, so, gas will flow until
the differential pressure across the MFC falls to zero. The line
could be at full N2 system pressure.<br>
<br>
Isolating the N2 from the MFC would prevent this. Shutting the 3 way
valve did not work on S4. I noticed the C4F10 manifold side of the 3
way valve was pressurized to full N2 supply pressure. That is a
problem likely associated with a defective 3 way valve. These are
old valves, but worked fine up to now. They will need replaced.<br>
<br>
What are our short term options?<br>
From now on, do not cap the lines once they are removed from the
detectors. That will prevent any buildup of pressure. Use aluminum
foil at the end to prevent debris from entering the line.<br>
Unplug the gas supply solenoid power connector for the sector to be
worked on to prevent to flow of gas.<br>
<br>
What are the longer term options?<br>
The C4F10 manifold and 3 way valves could be replaced with 2 way 90
degree valves to provide positive shut off off the N2 supply. This
could be completed is a day.<br>
<br>
George<br>
<br>
<br>
<div class="moz-cite-prefix">On 8/30/2017 1:19 PM, Morgan Cook
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:1348685215.5822695.1504113553802.JavaMail.zimbra@jlab.org">
<pre wrap="">
Marc,
Please take a look at the LTCC gas system. David disconnected sector 5 and capped both ends after you changed the setpoint and he closed the 3-way valve on Tuesday. Just now he went to tie the supply and return together and the supply side was under a lot of pressure. As I mentioned earlier, the same thing happened with sector 4.
Thanks,
Morgan
----- Original Message -----
From: "Maurizio Ungaro" <a class="moz-txt-link-rfc2396E" href="mailto:ungaro@jlab.org"><ungaro@jlab.org></a>
To: "Brian Eng" <a class="moz-txt-link-rfc2396E" href="mailto:beng@jlab.org"><beng@jlab.org></a>
Cc: <a class="moz-txt-link-abbreviated" href="mailto:dsg-hallbgas@jlab.org">dsg-hallbgas@jlab.org</a>, "David Anderson" <a class="moz-txt-link-rfc2396E" href="mailto:dla@jlab.org"><dla@jlab.org></a>
Sent: Tuesday, August 29, 2017 10:31:13 AM
Subject: Re: [Dsg-hallbgas] LTCC sectors 3 and 5
Hi Brian,
Ah that help. It looks to me that there is still drop in pressure, uncorrelated with weather.
Looking forward to your new extrapolation of leak rates.
Thanks,
Mauri
</pre>
<blockquote type="cite">
<pre wrap="">On Aug 29, 2017, at 10:24 AM, Brian Eng <a class="moz-txt-link-rfc2396E" href="mailto:beng@jlab.org"><beng@jlab.org></a> wrote:
Mauri,
That "significant drop" you were referring to yesterday is just due to the deadband of the archiver (0.1 slm) so all of the spots where it doesn't have a spike should be considered equivalent to zero.
If you zoom out a bit further and add the sector pressure as well you can see there is a significant difference from when the detector was attached versus when it was removed.
Namely the amount of time the flow is on (~30 min vs ~3 sec) and how high the pressure gets when the flow is applied.
George has mentioned that the 3-way valves used to turn off the gas are quite old and difficult to put in the completely closed position.
----- Original Message -----
</pre>
<blockquote type="cite">
<pre wrap="">From: "Maurizio Ungaro" <a class="moz-txt-link-rfc2396E" href="mailto:ungaro@jlab.org"><ungaro@jlab.org></a>
To: <a class="moz-txt-link-abbreviated" href="mailto:dsg-hallbgas@jlab.org">dsg-hallbgas@jlab.org</a>, "David Anderson" <a class="moz-txt-link-rfc2396E" href="mailto:dla@jlab.org"><dla@jlab.org></a>, "Stepan Stepanyan" <a class="moz-txt-link-rfc2396E" href="mailto:stepanya@jlab.org"><stepanya@jlab.org></a>
Sent: Tuesday, August 29, 2017 9:28:26 AM
Subject: Re: [Dsg-hallbgas] LTCC sectors 3 and 5
</pre>
</blockquote>
<pre wrap="">
</pre>
<blockquote type="cite">
<pre wrap="">Hi Brian, Marc, David,
If I understood correctly (please correct me if I'm wrong) Dave bypassed S4 box
(i.e. jumped the 2 ends together) on Friday the 25.
On the flow chart for S4 I see a signigicant drop yesterday right after 8am, but
not much on Friday, see attached plot, not sure how to interpret it.
Could you update on the leaks calculations for S4, and give updates in general,
both on leak checks and leaks measured, when available?
Thanks so much for this important work,
Mauri
On Aug 29, 2017, at 8:51 AM, Marc McMullen < <a class="moz-txt-link-abbreviated" href="mailto:mcmullen@jlab.org">mcmullen@jlab.org</a> > wrote:
-------- Forwarded Message --------
Subject: Re: LTCC sectors 3 and 5
Date: Tue, 29 Aug 2017 08:43:32 -0400
From: Marc McMullen <a class="moz-txt-link-rfc2396E" href="mailto:mcmullen@jlab.org"><mcmullen@jlab.org></a>
To: Morgan Cook <a class="moz-txt-link-rfc2396E" href="mailto:mcookiv@jlab.org"><mcookiv@jlab.org></a>
CC: Dsg-hallbgas <a class="moz-txt-link-rfc2396E" href="mailto:dsg-hallbgas-bounces@jlab.org"><dsg-hallbgas-bounces@jlab.org></a> , David Anderson
<a class="moz-txt-link-rfc2396E" href="mailto:dla@jlab.org"><dla@jlab.org></a>
Hi Morgan,
I have changed the setpoint on the MFCs to 0 for S3 and S5. Before David
starts his work, he should change the valve position on the 3 way valve
for those two sectors to the close position which is straight down
(90deg from current).
Thanks,
Marc
On 8/29/2017 7:14 AM, Morgan Cook wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Mark,
Please shut off the gas to LTCC sectors 3 and 5. David is going to leak check
them. In addition, please let us know when the gas is off.
Thanks,
Morgan
</pre>
</blockquote>
<pre wrap="">
--
Marc McMullen
Detector Support Group
757-269-7738
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<pre wrap=""><Screen Shot 2017-08-29 at 10.16.23 AM.png>
</pre>
</blockquote>
<pre wrap="">
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</pre>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
George Jacobs
Jefferson Lab (TJNAF)
STE 12
12000 Jefferson Ave.
Newport News, VA 23606
(office) 757-269-7115
(cell) 757-876-0480
(email) <a class="moz-txt-link-abbreviated" href="mailto:jacobsg@jlab.org">jacobsg@jlab.org</a>
(website) <a class="moz-txt-link-freetext" href="https://userweb.jlab.org/~jacobsg">https://userweb.jlab.org/~jacobsg</a></pre>
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