Summary from the Cold Probe Discussion at AMMRL’s meeting (48th ENC).
These notes depict each major component of the cold probe/cryoprobe systems.
1. Vacuum pumps: The Varian turbo pumps, that are on Generation 1 and 2 probes, should have the TIP seals changed every six months. Otherwise they will start pulling the load and will gradually wear out. Ion pumps are very reliable and have lifetimes of around 5 years if used properly.
2. Cold Head (CCC): Use grade 6 helium (highest purity available) and watch how you change tanks. The molecular sieve bed can be contaminated causing blockages that will reduce cooling performance. Cold head service can be pushed until the cold head dies at the risk of several months of down time, because engineers aren’t readily available. Plan ahead! MD10’s can go 2 years or more.
3. Cryobay Helium Compressor: It is recommended to change the charcoal filters for oil scrubbing about every 6 months on Leibert compressors. They have an approximate lifetime of about 5 years under optimal working conditions. Both Varian and Bruker have moved to Sumitomo helium compressors/cold heads on their latest cryogenic systems.
4. Electrical Outages: Several people have bypasses until backup generators start. Put the cold probe on emergency circuits and use UPSs for sites that have lots of electrical storms.
5. Heat exchangers and water chillers– Copper tubing on Haskris chillers will corrode over time specially if DI water is used. Opt for stainless steel if possible. Many people are using water-water heat exchangers. Filters in this case need to be monitored carefully. Water–air heat exchangers can work well depending on your site.
6. Boiloff from liquid N2 of the magnet can be used as your emergency eject air. See Jerry Hirshinger’s diagram.
7. $$$$$: Most of us didn’t project the long-term costs of running these probes. Cold head service and probe repair are expensive and you have to plan your budget accordingly. The general consensus was to push vendor maintenance back, but keep logs on your system.
Martha Morton, Ph. D.
Chemistry NMR Lab Director and
BBC NMR Facility Scientist
University of Connecticut
55 N. Eagleville Road, Unit 3060
Storrs, CT 06269-3060
(860)486-4069 (860)486-2981 (FAX)
Received on Thu Jun 25 2009 - 09:09:56 MST