Discussion Category:  Vacuum Pumps

Tip seal replacement question

I've just replaced the tip seals and exhaust valve on an fairly new/used edwards xds-10 pump and it is running hot (180°F)¬†after approximately 1 hour. It is pumping down to 1.2E-2 torr with no load.

Question is, why is it so hot? Is there a break-in period for the tip seals?

We have others in our pump chase (5) that run around 118°F.

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Asked by

stighe
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howard2012

The heat may be due to the tips seals contacting each other. Were the grooves cleaned as suggested prior to installing the new tips seals? Were the new tip seals pressed down into the grooves fully? Were the ends cut where recommended? The idea of the tip seals is to make the clearances as small as possible between the scrolls. This reduces the losses as the scrolls moves the trapped gas towards the center of the scroll, compressing it as it goes. I think it is common knowledge among users that there is often dust generated from the tip seals, especially if they are not installed correctly. This is a simple procedure, but should be carried out by someone with some previous experience. I'm not suggesting that you don't have this experience, just making a comment. Even a technician that has done this before can have problems. I suggest that the installation of the new tip seals be checked to make sure they are in correctly. Look for contact areas or wear spots, and see if you can feel any high spots. Did you watch the Edwards tip seal replacement video before the service was carried out?

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stighe

Howard,

Thanks for the reply and yes, watched the video and performed the replacement as directed. This particular pump had been sent out to "professional" rebuilders and after receiving it back and installing it, it began squealing after only a month (still pumped down well, just loud). That is why we are experimenting with replacing the seals ourselves. The scroll cavity was found with a lot of blackened soot like material (I have pics) so both scrolls were cleaned well with methanol & isopropyl alcohol (including grooves). Seals installed and cut where directed (indicator line on the head and 20mm from the end on the motor side. I have since disassembled and inspected it and have found some very minor "shedding" of seal material which I assumed was probably normal break-in but outside of that, nothing alarming.

Howard, I'm unclear as to your suggestion that they may be contacting "each other". They seal to opposite faces and are wholly contained within their respective grooves.

I will admit this is my first seal replacement but feel I understand the mechanics and attempted to be meticulous in the re-assembly but none-the-less it's running hot and that's not right. I'm beginning to wonder whether it was running hot with the previous rebuild and that's why the soot like material was there in the first place. I have some pics and a .mov file for reference if you're interested. I tried sending them to your hotmail address but it got bounced. UPDATE: Howard, I've been thinking over this issue since posting the above comment and I think I know what you meant. Tip seal face to metal face of opposite scroll should be a minimum spacing but not in hard contact. Is that correct? If so, then that is the issue. On start-up this pump lagged in rpm's initially and then seemed to reach full speed. Also, if what I think you meant by contacting each other is correct there should be "no" shedding. Is that correct? Also, are these scroll heads and pump bodies serialized and mated? Are the scroll heads interchangable from pump to pump? Is there an adjustment for mating pressure or distance between these scroll assemblies (vanes?)? Thanks

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