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Cryopump Troubleshooting

The following troubleshooting tips cover very basic cryopump maintenance and troubleshooting. If you require detailed technical assistance please contact the pump manufacturer. You are of course welcome to contact SFC with questions.

Most cryopumps provide years of trouble-free operation with little maintenance and down time. These pumps are not maintenance-free however and knowing when and what to service can save time and money on expensive overhauls or replacements. Always follow the cryopump manufacturers instructions located in the system manual.

The following tips cover a few of the more common problems encountered when operating cryopumps.

Symptom: Increase in ultimate pressure or normal operating temperature.

Unlike a turbo or diffusion vacuum pump the cryopump retains all of the gases it has pumped and will eventually need to be emptied. (Regeneration) Generally, If the compressor is operating, the cold head is quietly turning and the temperature is in the normal range, the only possible cause of pressure increase is a full pump or increased gas load such as a leak. Perform a helium leak test on the vacuum system and regenerate the cryopump per the manufacturers instructions.

Symptom: Cryopump failing rate-of-rise-test after regeneration. Regeneration completed but pressure and temperature problems still exist.

If the cryopump has been exposed to atmosphere while cold, an additional or extended regeneration may be necessary.  Roughing the cryopump for extended periods or opening the rough valve while the pump is cold can allow contamination from mechanical pump oil back-streaming. The interval between array replacement varies greatly depending on the type and conditions of normal use. If the extra regeneration does not correct the problem the 15K Charcoal array may need to be replaced.

Symptom: The cold head is making strange noises.

If the cold head runs smoothly until it has begun to cool and suddenly starts to make ratcheting sounds or otherwise stops turning smoothly, the helium circuit has become contaminated. Severe contamination may cause the pump mechanism to seize. Perform the decontamination procedure per manufacturers instructions. This procedure is not difficult but does require a maintenance manifold and care should be taken to follow the instructions closely.

Compressors:

If the cryopump compressor starts and continues to run for half an hour it's probably okay. It may require service but at least it's not dead. The adsorber should be changed at the proper intervals as specified by the manufacturer. If not changed the adsorber can allow compressor oil into the helium circuit which can lead to costly repairs. Adsorber replacement for most compressors is a simple task but again, the installation instructions should be followed closely.

Correct helium pressure within the compressor is very important. Low pressure can result in high pump temperature and may indicate a leak in the helium circuit. Higher than normal pressure can cause the compressor overload to trip. Check both static and dynamic pressures against the specifications for your specific unit. If you find you are having to add helium more than once or twice a year, there is probably a leak somewhere in the helium circuit. Use a helium leak detector to isolate the leak.

Improper line voltage, frequency and phase can cause numerous cryopump system malfunctions. Insure that the compressor and pump are connected exactly as indicated in the installation manual and verify the proper voltage and phase of input power. Symptoms of improper power connections and/or connections can include complete failure to operate, sluggish or stopped cold head operation, tripping of compressor breakers, and others. Check the installation manual for power requirements and connections.

Specialty Fluids Company is not affiliated with Brooks Automation or Austin Scientific in any way.

1Cryo-Torr, OnBoard, CTI-Cryogenics, CT-8 and CT-10 are registered trademarks of Helix Technology Corp., Brooks Automation

2Cryo-Plex is a registered trademark of Austin Scientific Co., Oxford Instruments

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