Cleaning Foreline backstream and servicing diff pump

[MSCHemist]

So I spoke with Edwards vacuum support. They seem to indicate backstreaming from the foreline pump is an inherrent issue.

Back streaming occurs at pressures below about 2 x 10-2 mbar. It is oil vapor that travels back up into the system due to lack of significant gas flow into the pump to suppress it. A foreline trap will prevent this. This is what the customer is experiencing is my guess. Use the FL20K and adapters to fix this problem.

Suck back, is liquid oil being drawn into the vacuum line when the pump is turned off. It does not occur when the pump is running.

So is it possible the diff pump is not allowing enough gas flow into the foreline pump and setting up the conditions for the backstreaming?

I recently replaced the lubricating wick on my turbo pump and about a ml or so of oil came out the bottom but I otherwise never notice any back-streaming.

[James_Ball]

If the line has more than a film of oil on it then you are probably getting the suck back condition because the valve is bad. I never saw that on the small Edwards pumps, but the 5975 we have that came with a Pfieffer pump would always fill the tube up about 4 inches every time we shut it down. It was also the first one that died completely.

The amount of flow shouldn't be limited by the diffusion pump, if it was then you would have terrible vacuum in the analyzer. You only have 1-2ml/minute flow through the column so that is all you will have going into the rough pump. If you are getting backstreaming of vapor because of too little flow through the pump you may need to open the ballast valve a little to introduce more flow through the pump.

[TheFlIrishman]

Yea I've found the 5972 manual. If the diff pumps are similar or identical there is simply a S shaped spring rod that holds the stack parts down and the hole in the stack needs to face the diff pump outlet.

Though if Santovac is a glycol why use MeCl2? At least ethylene and propylene glycol are totally insoluble in MeCl2. MeOH is a better bet but MeCl2 has a lower boiling point.

Any chance of us getting a pdf copy of hte 5972 manual - were just starting to put a 5890/5972 system together. G Kenney, Eastern Florida State College

[MSCHemist]

http://www.analyticalinstrumentservicec ... 6890hw.pdf