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Pixel Cooling System Modifications. C. Newsom December 17, 2009 University of Iowa. 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.
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Pixel Cooling System Modifications C. Newsom December 17, 2009 University of Iowa
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.
Color Code • Items in blue are differences with the proposal of Hans. • Items in black are not. • Items in green are informational.
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 at an accelerator complex. I was spokesman of the experiment that was affected. • Why triplicate (minimum) redundancy? First, this is the recommendation of Rich Schmitt. Second, I personally have seen 3 cooling systems fail simultaneously. Often one failure triggers others.
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 routinely use the supply and return Schrader valves for filling, draining and air evacuation. We thus recommend that either • there be one Schrader valve on each supply and return line or • that there be one Schrader valve on each supply and returnmanifold. 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).
General Manifold Changes Supply and Return Manifold Drain/Fill/Evacuation Pressurization Point Manual or Remote Isolation Valve In this option we can dispense with all 18 supply loop Schrader valves and all 18 controlled apertures. We end up with 8 taps total on the loops (4 supply, 4 return).
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.
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.
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…
Safety Summary • High 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)
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…