Fighting with the Opti-Temp Diffusion Pump Water Chiller

"If you have seen one of those scary late night pimple medication ointment advertisement which shows horrible pictures of before/after then I have another for you right here. The Opti-Temp water pump from our Ultrafast Nanoscale Electron Diffraction Imaging and Spectroscopy (UED) Laboratory has obviously not been cleaned regularly or at least not even a single time during the past five years."

The pump has been exhibiting some serious overheating of the inside electric motor as well as unusually hot overall heat dissipation through vent holes. I first could not pinpoint the source of problem. In fact, few weeks ago, for about a week I called the company almost everyday for troubleshooting the overheat problem which almost always led to abrupt shut-down of electric motor.

The calls usually lasted almost for an hour everyday. Paul, who was very kind enough to help me on the phone even after his regular shift, didn't seem to pinpoint the source of the problem either.

The problem was, if I let the motor run for about ten minutes, the electric motor got heated up gradually until it became so hot to the point that keeping my fingers on the motor chassis became a painful thing. Then after a while the motor started to exhibit a periodic turn-off-turn-on cycle with a period of about 4 seconds and after ten to fifteen seconds, the whole electric pump shut down abruptly.

I first suspected the cooling elements inside the chamber since I thought they were the ones responsible. When I opened the ventilation, the heat exchangers highly clogged with all sorts of dusts (below pictures) seemed to support my opinion. I called my lab partner Terry for any vacuum cleaner for this purpose and once I found one it took me about a sole ten minute to give it a new fancy look.



I fired the pump up again, this time with an absolute certainty that the pump will continuously run without overheating. Guess what, the problem still persisted. So I began to suspect other mechanical components such as compressor oil levels being too low, etc.... but all in vein. I called Paul again with absolutely no idea how to fix this but this seemed to apply to Paul himself as well. He suggested me to take out the electric compartments of the motor and measure the power (electric) feeds to the motor. As far as my voltage and amperage measurements go, they were normal except when the motor turned off, I read zero voltage. 

I moved onto the mechanical relay (solenoid) which controls voltage potentials across the motor. In case the motor fails, if this solenoid is triggered, then I know for sure that the solenoid has got some problem. But the relay was normal! What the...

After about an hour, Paul almost sounded like he was giving up. Then as a last resort, he asked me to check the flow adjuster inside. A flow adjuster is an element that controls pressure differential level inside the piping. Depending the amount of the developed pressure differential, flow speed can be adjusted. Therefore I sometimes call it just "speed adjuster." According to him, the default setting of this thing is around 50 psi (80psi either one of these numbers. I'm not quite sure right now). But if I go well over this limit, the motor has to do extra work to pump out waters which can overheat it and after a certain period of time this can trigger the thermal actuator inside the pump shutting the motor down, thus protecting it from thermal damage.

This must be it since I was basically driving the motor as high as possible to overcome the ridiculous long length of the water pipings going around the diffusion pump. I immediately turned the flow adjuster setting back to a position where I read a flow rate of 2.0 gpm (the flow rate at the maximum was 2.8 gpm) and all of a sudden the motor started to behave nice and beautiful.

I felt so stupid for wasting my time (and probably his time) for something that is as simple as like this. If you put too much work load on a small motor, it will get overheat, as simple as that. Man, thank god that the motor is thermally protected, unless I would have ended up frying the motor and, who knows, it may have gone a little further to knock down a 3-phase high voltage power line. Good stuff.

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