Fusor Forums

Can DC-704 have an "almost" failure?

The oil I have installed now sat in a partial container for a few months before use. I did allow air into my pump by accident for a brief few seconds in recent testing.

I've read about oil failure where the oil becomes sludge. I've inspected my pump by shining a light down into the boiler and there is no sludge. It's hard to see well at the bottom of the pump though. The oil that was clinging to the removed jet assembly was perfectly clear.

I can pump down to only .003 Torr currently. The system holds fairly tight with no pumps running. I'm at a loss to figure out why I can't get <10E-4 Torr any more. I had a big problem a few weeks ago and have had every joint apart and put back together since then. I've got all the same quality of gear I had before plus I upgraded to stainless swageloks. I'm pulling my hair out. Maybe some comments from you guys will inspire me.

Thanks,
Jason C. Wells

704 is a silicone and it does not react to air like the the old mineral oils. What my have happened is you blew a bunch of oil out the foreline into the mechanical pump and there is no longer enough in the diff pump. Open it and check the level if it does not have a dip stick.

Jason
When you removed the jet assembly did you notice the outlet hole position near the base of the jet assembly. This has to face the backing outlet.
Also a diff pump that has been up at air for a long time can take a couple of hours to self degas before it pumps.
The last point is the heater in good contact with the bottom of the pump -rust -buckling- correct tension are all important here

Thanks you guys. I will check all of these things.

Regards,
Jason

Jason
When you removed the jet assembly did you notice the outlet hole position near the base of the jet assembly. This has to face the backing outlet.
Also a diff pump that has been up at air for a long time can take a couple of hours to self degas before it pumps.
The last point is the heater in good contact with the bottom of the pump -rust -buckling- correct tension are all important here

I did not know it also and I am very thankful for this good information.

This follow up is a little bit late. It may also be out of sequence with the advice given.

I did take the diff pump apart. It was too full. I sucked some rough pump oil up into the diff pump and also up into the gauge lines to the manometer that I had connected to the rough side. I do not believe that I ever left the isolation valve on my rough pump open with the rough pump stopped. That was one of the very first mistakes I made in this endeavor a couple years ago. Maybe the oil leaked past the rough pump isolation valve (part of the pump itself).

So I still don't know what my original problem was, but I do know what this recent problem was. Now I am on a different path since I have brandy new DC-704 installed in my diff pump.

Regards,
Jason C. Wells