Pixel Cooling System Modifications

C. Newsom

December 17, 2009

University of Iowa

Basic Requirements

1. Safety – Have at least 3 redundant protection means for each section of the chiller (pump side, reservoir side).

2. Reduce maximum possible pressure in the system.

3. Efficient filling, draining and evacuation.

4. Efficient pump replacement when needed.

5. Removal of inappropriate materials.

6. 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

1. 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.

2. We routinely use the supply and return Schrader valves for filling, draining and air evacuation. We thus recommend that either

1. there be one Schrader valve on each supply and return line or2. 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).

General Manifold Changes

Manual or RemoteIsolation Valve

Drain/Fill/EvacuationPressurization Point

Supply and Return Manifold

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

1. Reduce the max pressure by replacing the pump.

2. Install the new pump with flanges for ease of removal in case of failure (3 have failed after ~1 year of operations).

3. Add one backflow regulator to the system in parallel to the manual bypass valve. (Replaces the old pressure relief valve.)

4. Straighten the plumbing near the pump.

Miscellaneous Details

1. Upgrade the pressure switch to a max of 3.5 barg.

2. Set the reservoir pressure relief valves at 0.5barg.

3. Fix any inappropriate welds/fittings/brazes.

4. 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 side1. Max pump pressure (new)2. Backflow regulator (new) 3. Pressure switch (exists)4. Control valve sensor (exists)

• Lower pressure side1. Pressure relief valve (exists)2. 2nd Pressure relief valve (exists)3. Air pressure regulator (exists)4. 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…