Chromatography Forum

I had my Varian GC 3400 running for over 2 weeks non-stop with an auto-sampler.

Today the aerator ("fan") inside the oven suddenly started producing a sharp whistling sound. I believe it lacks some lubricant...? Is that possible? Anybody had that before? As far as I could see, nothing was broken, but the sound was loud and kind of unpleasant / dangerous.

Is the set screw holding the blades in place a little loose? Is the fan rotor spinning inside the blades?

Are the blades hitting or striking the inside of the oven?

best wishes,

Rodney George

Rodney, thanks for asking these questions. I checked all that - negative. Screw is fixed, blades don't touch the oven. Inside the oven the turn easily, outside the oven the same (the "PABST" PC-style fan). I also heated the oven to 80 degrees and went down to 50 degrees - everything seemed to be fine. Maybe a I do a full run again and see what happens (self-repair?).

Do you know if there are ANY rotating parts which need lubrication? I mean, I doubt it... just to be sure. Thanks again.

Stephan

The bearings inside the fan motor are then the most likely cause.

Some motors can be lubricated. Others have to be replaced.

Good luck,

Rodney George

Thank you.

I had similar problems with the 3400

The fan motor of the Varian 3400 is some cheap dirt manufactured in an already long gone factory. The bearings fail due to thermal stress.

The original manufacturer doesn't have this motor or a similar replacement in its current inventory. Old stock must not be sold as Varian vetoed the sell to anybody besides them.

Now to fixing the motor: The housing is two-part and fixed at three points with bended metal joints. Open these joints and remove the coil
You'll find that the insanely cheap isolation laquer will brittle away. We'll take care of that later.

Now to the bearings: Quality motors from Europe would have a punch mark on the shaft to detract the bearings. You'll have to make your own punch mark with a fitting tool (and good visual judgement). Then detract the groove ball bearings, type 608 2Z from the shaft and mount new ones.

Now mount the coil again and use silicon tubing to isulate the power wires as the isolation of the wires is a not thermally stable, potentially dangerous PVC derivate which can cause short-circuits etc.

Mount the motor again and you're done
I've fixed at least two motors that way

Wow! This is cool. May I add that these groove ball bearings can be bought at German electronic supplier www.CONRAD.de under the part number 198515, as you told me in a private message. BIG HELP! Thx!