Around 10pm on Sunday Oct 22 beam was tripped multiple times due to low flow for the T1 collimator cooling circuit (B1A:T1:FGCOL).  Temperature of the collimator (TC7COL, TC8COL) was monitored with reduced beam current and no increase was observed leading to the conclusion that flow was OK and the flow gauge was faulty.  Normal operation continued until around 1:30am on Oct 26 when the collimator thermocouples both rose quickly, causing the beam to trip when they reached 60C.  At this point we concluded that there was no longer flow in the cooling circuit.  1A was defined off and shielding was removed down to the T1 cooling package.  The problem was found to be the solenoid valve which would open when actuated, but close in less than a second.  The flow meter was checked, appeared fine, and the paddle wheel was changed anyways.  The solenoid part of the valve was replaced (valve body not changed), which solved the problem.  Flow returned to 0.7gpm and the collimator thermocouples returned to normal value.  It is suspected that the valve was fluttering open and closed causing the decreased flow observed before, and then the valve finally failed closed at 1:30 on the 26th.