1. Pixel Cooling System Modifications
C. Newsom
December 17, 2009
University of Iowa

2. Basic Requirements
Safety – Have at least 3 redundant protection means for each section of the chiller (pump side, reservoir side).
Reduce maximum possible pressure in the system.
Efficient filling, draining and evacuation.
Efficient pump replacement when needed.
Removal of inappropriate materials.
Minimal intervention.

3. Detector Safety Has the Highest Priority
For those who say that the existing and proposed systems with higher potential pressures (7 barg with present pump) cannot possibly fail are simply wrong. I was present when such a system did fail. I was spokesman of the experiment that was affected.
Why triplicate (minimum) redundancy? I personally have seen 3 systems fail simultaneously. Often one failure triggers others.

4. Manifold Modifications
Paula Tropea has suggested (Dec 15) that we replace the manifold TA valves and solenoids, remove the plastic tubes and controlled orfices and remove the Schrader valves. I have no problem with these suggestions if a few other steps are taken.
We use the supply and return Schrader valves for filling, draining and air evacuation. We thus recommend that either
there be one Scrader valve on each supply and return line or
that there be one Schrader valve on each supply and return manifold.
Note: To fill and drain individual loops it will be necessary to drain the chiller as well. If this is not desirable this can be obviated by adding a manual valve to each supply and return manifold line (8 valves).

5. Chiller Section Modifications
Reduce the max pressure by replacing the pump.
Install the new pump with flanges for ease of removal in case of failure (3 have failed after ~1 year of operations).
Add one backflow regulator to the system in parallel to the manual bypass valve. (Replaces the old pressure relief valve.)
Straighten the plumbing near the pump.

6. Miscellaneous Details
Upgrade the pressure switch to a max of 3.5 barg.
Set the reservoir pressure relief valves at 0.5barg.
Fix any inappropriate welds/fittings/brazes.
Fix the cross connections above the plant.

7. One more safety suggestion
Put a manual switch on the chiller so that when maintenance is being performed the station can be “locked out”.
This should apply to all proposals…

8. Safety Summary High pressure side Lower pressure side
Max pump pressure (new)
Backflow regulator (new)
Pressure switch (exists)
Control valve sensor (exists)
Lower pressure side
Pressure relief valve (exists)
2nd Pressure relief valve (exists)
Air pressure regulator (exists)
Pressure sensor (exists)

9. Backup Materials
The current system can provide a maximum pressure of 7 barg (no flow).
I take safety seriously. Here is why.
I have been nearly electrocuted 3 times. Each was the result of human (not mine) error.
I have seen a flood submerge every transformer providing main power to a lab.
I have seen rain short circuit a giant accumulator.
I have seen lightning destroy equipment I was using.
I have observed three independent cooling systems fail simultaneously.
I observed a massive pressure overload on a system that ran without problems for at least 5 years.
I have been irradiated because of a radiation protection system failure.
My best friend was irradiated because of an inadequate radiation protection system.
I was nearby when a large magnet picked up an unsecured pressure bottle and sucked it into the center of a spectrometer, destroying part of an experiment.
There are many more…