Turbo shut down with high foreline pressure

[David Kunkle]

I did not mean to poo-poo Turbos, of course. A working turbo is a wonderful thing. The key word is "working", however, and one that is not working can cause a lot of money to be sunk in a lost cause. Their would be a point for me where I would cut my losses.

Richard Hull

Even if this can't be fixed, I'll probably stick with a turbo due to my needs. I also have a point where I would cut my losses, and I believe I'm just about there. I just hate to chuck this one for want of a bearing or before I know for sure it's a lost cause.

[David Kunkle]

Post pics of each side of the old bearing and I can tell you if it is angular contact.

Here you go. Hope they're clear enough- this is the best I could get out of my camera.

[Jerry Biehler]

I meant the old bearing that did not fry.

[David Kunkle]

I meant the old bearing that did not fry.

All the upper bearings including the original are fried- the photos are of the original.

I still have the original lower bearing that the GMN engineer and I also talked about. One thing he asked me about is this: The distance on that between the inner race and the cage is wider on the upper or imprinted side of the bearing than it is on the other side. The engineer said that indicates an angular contact. Is that what you're looking for in a photo of the intact bearing by chance? If the lower bearing is angular contact, I believe that makes the upper one necessarily angular contact also according to what I've learned.

[Jerry Biehler]

Yeah, that sounds like AC. But like I said before, AC bearings must be ran in pairs otherwise there is nothing holding them against their race. And the preload must be set, this could be done in a number of different ways like shims or the races are ground to create the preload when installed. If there is no preload the balls will just skate over the surface and die kind of like you have experienced. Probably the reason the bottom one did not fail is there is pressure on the race from the weight of the rotor.

It is possible the upper was AC, but unless you have the means to properly set the preload you will probably continue to have bearing failure.

[Doug Browning]

I have a Pfeiffer TPU 060 apart for bearing replacement here. Looking at the old bearing, the inner race has a taper on one side, which would make for a larger gap between the inner and outer race when assembled. However, the actual ball track in the center of either the inner or outer races appears symmetrical, so I assume that is not an axial load type bearing. I would suspect the inner race taper is merely for assembly purposes, likely pops together, maybe with some heat on the outer race. In any case, I got an ordinary $40 ceramic bearing to put in, so I'll be finding out how well that works.

The motor itself will exert some axial centering magnetic forces between the rotor and stator, so I guess it would depend on how heavy the rotor is, as to whether additional axial bearing forces would be needed.

One thing that would give me second thoughts about a pre-loaded bearing setup, is that if the rotor gets hot, it may expand enough to bow slightly and cause a balance problem at high speed. Makes me wonder if the bearing assembly/mount in the Pfeiffer should be left with just a little end slack when assembled. Although it would just push against the magnetic bearing up top, which has got axial lee-way. (see below) You may want to find out about the tightening requirements / recommendations for the model or general design type at hand.

I also have a TPH 190 here off Ebay, and while it spins freely and revs up, I can hear a little bearing noise, so it will be the next Guinea pig for a ceramic bearing replacement after the TPU 060 is running happily. It appears to have a grey ceramic bearing in it now.

And then there is the TPU 240 I got off Ebay, which revs up silently, but it has an obvious end play in the rotor when shaken, which is bi-stable, like the magnetic bearing is popping in and out of alignment. Almost seems like someone left an O-ring out when they replaced the lower bearing, but I suspect they put in a narrower bearing than the original and it is not tightening up properly when re-assembled. Another ceramic bearing I think. I haven't pulled the bearing yet, and I don't know what the proper width should be. But none of the other turbo units have this end play issue. (the TPH 190 and TPU 240 look like they have identical construction, so I guess I could pull the bearings to compare. But I hate to tear into the 240 if it isn't really a problem.) So I'm a little leery of running the thing until someone knowledgeable can comment on that issue.

It's pretty clear that most used turbo stuff off Ebay is there for a reason now.

Fortunately the Pfeiffers came off Ebay for relatively cheap ( no wonder) and I already had a working controller for them. So I'm really just experimenting with what it takes to fix and maintain them. I'm too cheap to buy the $70 Pfeiffer oil cartridges too, and I'm not adverse to trying out some mechanical pump oil on the lower bearing, if someone has a recommendation.....

In the meantime, several diffusion pumps are smoothly, silently pumping away, day after day. All one really needs to get them ultra clean for a turbo substitution is a water cooled baffle with maybe Santovac 5 diff oil in them. But I should add that diff pumps off Ebay typically have issues as well. I got a VHS-4 cheap, which was absolutely clogged up with clear plastic like stuff, big chunks, no idea what it was, fortunately it cleaned up well. Didn't hear anything about the fish in the river dying off yet. Never know what these things were used for. Some of the diff pumps on Ebay are missing the jet assembly, and then so many odd-custom inlet flanges, and then there are typically odd heater voltages, the heater may not work, and the model is totally obsolete so no heater replacements are around. I would stick with well known brands that have 2nd source heaters available. Disc heaters are much easier to change typically than cartridge heaters.

[David Kunkle]

Yeah, that sounds like AC. But like I said before, AC bearings must be ran in pairs otherwise there is nothing holding them against their race. And the preload must be set, this could be done in a number of different ways like shims or the races are ground to create the preload when installed. If there is no preload the balls will just skate over the surface and die kind of like you have experienced. Probably the reason the bottom one did not fail is there is pressure on the race from the weight of the rotor.

It is possible the upper was AC, but unless you have the means to properly set the preload you will probably continue to have bearing failure.

I've realized there are 3 tiny leaf springs that just contact the upper side of the outer race. This pic is actually off Andrew's web page 'cause my camera sucks:

They look like 3 little bluish tabs. The bearing sits loosely in that assembly- nothing actually holding it in. After putting that bearing assembly back in, and when the 4 outer screws are tightened, it's easy to see now that the 3 little spring tabs are pushed upwards by the bearing and exert force back down on the outer bearing race. There's my pre-load. These spring tabs were always completely flat each time I took it apart and have not been bent, etc. There's no way to alter/adjust this. I suppose I could bend them up or down to alter the pre-load- I wouldn't even know which way to go or how much. One theory I now have is that the original bearing failed from old age, this literally welded the ball bearings to the inner race. Some balls were quite difficult to break off. That has to be a lot of heat generated and transferred to these spring tabs. I wonder if the heat could've ruined their spring rate and thus the series of new bearing failures? If there was a manual in existence for this pump, maybe it would say the spring tabs must be replaced after a bearing failure. Good luck finding new ones, though.

[Jerry Biehler]

I dont think those set any kind of preload. They are pretty generic bearing retainers. I have never seen anything like that used to set preload on a bearing.

[David Kunkle]

After Jerry's last post, I'm completely out of ideas now. Even just got done painstakingly checking the motor assembly for anything that could have gotten cock-eyed on re-assembly and can find nothing. I don't intend another attempt at this turbo. I couldn't fix it, but I may have fixed it so it can't be fixed.

Anyway, I have been intermittently searching ebay and pchemlabs, duniway, etc. since this pump went belly up. Main search was for something complete with controller and cables, and newer. As many of you know, that's make for a pretty short list. But I found this from lab-equipment-list, 100% + feedback.

http://www.ebay.com/itm/Edwards-Turbomo ... fresh=true Have to scroll down a bit to see it, now that it's sold.

Built in 1999. Seem to be a lot of these for sale - hopefully that means they were popular. Duniway, etc. all rebuild and sell these = parts available. Even found a manual off the web easily.

In an email exchange they replied:
Hello-
The unit was pulled from a working Mass Spectrometer that was just removed from service by our techs.
We have not fully tested the unit, but we will give you a 30 day warranty on the unit.
If for any reason you do not like the unit, just send it back for a full refund including shipping both ways.

They were asking $2200. Sent them an offer of $1800 on Friday half jokingly- thinking they would reject it, and soon after I got an acceptance email.

Only down side is that the old turbo used a 6" CF, and just about everything out there including this Edwards uses a 100 ISO. Probably looking at $200 more for the LDS order and welding to swap out flanges. On the upside, the chamber is already torn down and sitting at the weld shop getting a leak fixed.