At approximately 13:50 today the T2 cooling system secondary side solenoid valve (T2CS:SVSEC) failed to a closed position.  This was the same location where the valve failed on July 10th (E-Log #224), and also in Nov 2016 (E-Log #211).  This repeated failure does not seem like a coincidence, so instead of replacing the valve with a new unit, it was bypassed temporarily until we can determine the cause of the failures.  A 3/4" FNPT coupling was installed in the place of the valve, and a CPC-4 stub was plugged into the control cable with pins 1 and 2 shorted in order to prevent the control system from timing out.  The cooling system has now been restarted and water is flowing properly through both sides of the system.  These failures must be investigated further during the fall shutdown, and ideally a solenoid valve should be reinstalled at this location (currently to shut off water supply to the secondary side the 1A tunnel must be entered to access the CuALCW supply valve).

Prior to shutting off the system for repairs some tests were performed by Tony Tateyama who provided the following summary:  "I wanted to see if there was any possibility of anomalous signals for T2CS:SVSEC drive & loop-back voltages at the PLC BOP.  Approximately 23.8 VDC was seen for the drive signal & slightly less for the loop-back signal.  In addition, about 70 mVAC ripple was also observed.  The same measurements were done for the T1CS:SVSEC voltages for comparison.  Approximately 23.9 VDC measured for the drive signal, and again, slightly less (~23.8 VDC) for the loop-back signal.  About 100 mVAC @ ~8 kHz was also seen. "