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User name Jack (Techs)
Log entry time 11:20:39 on May 21, 2008
Entry number 239066
keyword=Gas System
Looking in the EPICS archiver the gas system UPS seems to have gone down
at 2:50AM this morning. The system was restarted at 9:50AM. The UPS
supplies power to the pneumatic valve controllers, the system interlock
box and the monitoring VME crate. The VME crate only reads the status of
various things in the system. It is not used for any of the controls. So,
if the VME crate itself goes down that does not necessarily affect the
gas flow. If the Detectors Gas System Interlock Status unit loses power
it cannot send an indication of trouble to the display unit in the
Counting Room. The Counting Room will have no alarm from the display
unit, nor will any LEDs be lit. If the Detectors Gas System Interlock
loses power, the solenoids on the argon and ethane low pressure side of
the manifolds will close. The gas will stop flowing to the VDC gas mixing
subsystem. The VDC gas flow will not cease immediately. It looks like gas
stopped flowing through the VDCs at 3:45AM. When the pneumatic valve
controllers lose power the pneumatic valves close. These valves are on
the high pressure side of the manifolds, one for each cylinder. This will
close off each cylinder and no gas will flow out of them. If the
pneumatic valves are closed for a long enough time the pressure in the
nitrogen lines will bleed down low enough that even after power is
restored there is not enough residual pressure in the nitrogen line to
activate the pneumatic valves. In this case one needs to make sure the
Right side nitrogen cylinder is "online" and then open the bypass valve
by the Nitrogen manifold to charge the lines. Once the line is charged
and the pneumatic valves are functioning the bypass valve must be closed.