In my day job, I do a lot of work with mass spectrometers(not as much as I use to, but still as much as I can), and with mass spectrometers come high vacuum systems.
I'm in the midst of doing some major upgrades to one now, and am getting ready to convert its diffusion pump to a turbopump(turbomolecular pump). If anyone cares, it's a Hewlett-Packard 5973 mass spectrometer, and I'm installing a vacuum manifold and "High Performance" turbopump. The pump is Edwards branded but carries an Agilent part number. As far as I'm aware, though, it's an Edwards EXT250 series pump.
On older turbopumps(such as on the HP 5970 I once used), changing the turbopump oil was a routine task. Newer pumps, including the one used on the 5973, are supposed to be maintenance free and you basically run them until they die(and since they mostly ride on magnetic bearings once up to speed, the vast majority of wear occurs in starting and stopping, ones run for years at a time will often encounter little to no wear unless they ingest a lot of air).
In reading through the Edwards EXT250 manual, though, I realized that in fact the lower bearing is oiled. The manual implies that it's sealed for life, and of course should have little contact with the highest vacuum stages of the pump, although the manual does caution not to put too much of a vacuum on the foreline as it can cause oil evaporation. I'm not overly worried about this-I haven't yet powered the pump up, but HP/Agilent would have shipped the unit originally with a pitiful little Edwards E2M1.5 pump, which is a traditional oil-filled rotary vane pump(way too small for the application in mine and plenty of others opinion, plus it runs very hot which gives a high hydrocarbon background, and good for at best 1x10^-3 torr under ideal conditions but more like 1x10^-2 torr in the real world). Granted I'm ranting about this, and most of the independent service engineers I talk to don't like the small pumps either, but the 5973 came on the market in 1996 and the current 5977 ships with a comparable pump as standard, so I guess they don't have an issue with it. I'll be backing it with a Varian DS102, a much larger(and cooler running) pump capable of 1x10^-3 torr also, but in real world conditions can usually actually manage high 10^-3 torr vacuums. Edwards gives 1x10^-5 torr as "too high".
I'm wondering, though, has anyone ever changed the oil in one of these "sealed" pumps? Ideally I'd like this one to last me a LONG time, and if there was a way to get some more life out of it, I'd do it. At the same time, I don't want to mess with things that don't need to be messed with, even though I'm also not generally afraid of the "caution-no user serviceable parts inside" warnings.
If you have changed the oil, what do you use? I do actually have an ancient HP-branded bottle of oil meant for the Pfeiffer? pump on the 5970, but of course that would be 30+ years old and I'm sure there are better oils out there.
I'm in the midst of doing some major upgrades to one now, and am getting ready to convert its diffusion pump to a turbopump(turbomolecular pump). If anyone cares, it's a Hewlett-Packard 5973 mass spectrometer, and I'm installing a vacuum manifold and "High Performance" turbopump. The pump is Edwards branded but carries an Agilent part number. As far as I'm aware, though, it's an Edwards EXT250 series pump.
On older turbopumps(such as on the HP 5970 I once used), changing the turbopump oil was a routine task. Newer pumps, including the one used on the 5973, are supposed to be maintenance free and you basically run them until they die(and since they mostly ride on magnetic bearings once up to speed, the vast majority of wear occurs in starting and stopping, ones run for years at a time will often encounter little to no wear unless they ingest a lot of air).
In reading through the Edwards EXT250 manual, though, I realized that in fact the lower bearing is oiled. The manual implies that it's sealed for life, and of course should have little contact with the highest vacuum stages of the pump, although the manual does caution not to put too much of a vacuum on the foreline as it can cause oil evaporation. I'm not overly worried about this-I haven't yet powered the pump up, but HP/Agilent would have shipped the unit originally with a pitiful little Edwards E2M1.5 pump, which is a traditional oil-filled rotary vane pump(way too small for the application in mine and plenty of others opinion, plus it runs very hot which gives a high hydrocarbon background, and good for at best 1x10^-3 torr under ideal conditions but more like 1x10^-2 torr in the real world). Granted I'm ranting about this, and most of the independent service engineers I talk to don't like the small pumps either, but the 5973 came on the market in 1996 and the current 5977 ships with a comparable pump as standard, so I guess they don't have an issue with it. I'll be backing it with a Varian DS102, a much larger(and cooler running) pump capable of 1x10^-3 torr also, but in real world conditions can usually actually manage high 10^-3 torr vacuums. Edwards gives 1x10^-5 torr as "too high".
I'm wondering, though, has anyone ever changed the oil in one of these "sealed" pumps? Ideally I'd like this one to last me a LONG time, and if there was a way to get some more life out of it, I'd do it. At the same time, I don't want to mess with things that don't need to be messed with, even though I'm also not generally afraid of the "caution-no user serviceable parts inside" warnings.
If you have changed the oil, what do you use? I do actually have an ancient HP-branded bottle of oil meant for the Pfeiffer? pump on the 5970, but of course that would be 30+ years old and I'm sure there are better oils out there.
