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Subject: Re: regenerating a cryo pump

Date: 04/17/03 at 10:23 PM
Posted by: Pat McMahon
E-mail: patmcmahon@earthlink.net
Message Posted:

In Reply to: regenerating a cryo pump posted by Abhiram Govindaraju on 04/14/03 at 3:45 PM:

Hello Abhiram

There are several ways to regenerate a cryo-pump depending on what the gas load has been and how quickly you want to get the system back on line.

The first and simpliest way is to turn off the pump compressor and cold heads and let the pump warm up. I am assuming that you have a working vent valve on the pump. At some point the pump will suddenly and somewhat violently vent a large amount of gas. If the system is in a small closed room there may be a decrease in the amount of Oxygen available for breathing, so take this into consideration. Warming up to room temperature can take a lot of time. Over a weekend is what I usually allowed. Allowing that much gas to vent through the pump vent valve can also blow a lot of loose material out of the pump and some can adhere to the seals on the vent valve. I always make sure that I remove the vent valve (it simply unscrews) and clean off the "O" rings to avoid future leaks. After it has warmed the normal pumpdown and cooling cycle is begun.

A second method (as Jim has suggested) is to vent the pump with warm N2 gas and purge the accumulated gasses with the N2 as well as to speed up the heating of the pump. Afterward the pump can be restarted normally. There are systems available which can be easily installed to allow this to be done automatically.

A third method, and one that I have used often, is applicable only if the gas load in the pump is Argon or another inert gas from extended sputtering runs. It allows the pump to be almost fully regenerated and returned to service as quickly as possible. The procedure is this. Turn off the compressor and cold heads and allow the pump to warm until the venting takes place. When the venting has slowed, rough the pump to less than 500 microns and turn on the cold heads and compressor. Almost all the Argon will be vented and the stages in the pump will have only warmed enough to thaw those gasses. So you will not have to cool down as far as if you had fully warmed and turn around time will be shortened. I make it my practice to only used this "fast method" for two or three cycles before doing a full regeneration.

I hope this helps with the operation of your system.

Regards .

Pat McMahon

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