I would like to thank everyone who replied with information regarding the X-Stream icing problem, and a summary is given below. The problem is now almost cured, and I found the most important factors to be:
- the accurate positioning of the cryostream nozzle so that the crystal is the first thing the cold stream hits, rather than the pin - moisture / humidity - turbulence around the crystal - air-conditioning system blowing cold air close to the cryostream Thanks again Mark ******************************************************** From: Mark Agacan Monday - January 12, 2009 4:31 PM To: Mark Agacan Subject: X-Stream summary Apologies for this slightly off topic question: I am having a great deal of trouble with my X-Stream 2000 cryostream system and I wondered if other users have similar problems. I've replaced almost all components (new GAST compressors, helium recharges, filters, etc., etc.) in the last couple of months but there is almost always icing of any cryo within 10 - 20 minutes of mounting a loop, and it is adversely affecting data collections. It appears like there is too much moisture in the cold or wam streams but the tubes have been fully dried out as per Rigaku advice. This X-Stream is attached to a generator with inverted phi axis and and i'm wondering if this could be the source of the problem, as the X-Stream for another generator in the same laboratory with normal phi axis does not ice up. Can some sort of turbulence around the loop caused by backdraft from the cryo hitting the inverted phi axis / camera mount cause excess humidity and lead to icing on the pin, loop and crystal? Has anyone else got this problem? Any suggestions would be very gratefully appreciated. Best Wishes, Mark ********************************************************** Hi Mark We had a LOT of pain with icing, and it really comes down to one thing: water in the gN2. And don't expect to measure some other way whether you have it, because your X-stream (or Cobra) is the most sensitive water meter there is. In our case, the symptom was the X-stream (and later Cobra) blocking up after between several days and several hours. And we solved it by ditching the gN2 generators we were using, and organising boil-off gN2 (much purer). The secondary effect of sample icing: we'd see this as well if we had something (e.g. collimator) poking into the cold stream*: that causes turbulence which draws in moisture. Worst case you see ice flakes flick onto the crystal in real time; best case you get an ice ball after a few minutes to hours. (* technically, the stationary phase between the cold and warm streams.) Hope that helps. phx *************************************** Hi, If you have ice on the crystal (loop) but no blockages of the cryostream itself (and this seems to be what you're saying), it is unlikely to be a problem with the LN2 (although I only have experience with Oxford Crystreams, but I imagine this also applies to X-streams). Our main problems are turbulence (collimator poking into the gas stream(s) or gas 'bouncing' back from something just beyond the crystal - moving things even a little may help here) and drafts due to 'powerful' air-conditioning. As you state that one of your setups is affected and not the other, it may well be the case that an air conditioning vent is blowing onto your setup, and disturbing the gas streams. We resorted to hanging plastic sheeting around two sides of our set-up and this made a vast difference. HTH, Johan *********************************************** mark we also have an inverted phi, and so probably our layout is similar to yours (we're also rigaku). we had icing problems that were cured by directing the airflow from the a/c unit directly down, rather than across the room (and towards the x-stream). turn off your a/c, and see if a fresh cryo still ices up in 20-30 mins. if so, then re-direct the airflow or build a plastic tent! rick **************************************************** Hi Mark, In a similar setup (X-stream 2000, inverted phi, we have had no problem with our X-stream.) Cheers, Zsolt Dr. Zsolt Bocskei sanofi-aventis Chemical and Analytical Sciences 16 rue d'Ankara 67000 Strasbourg France ************************************************** We've been able to run months with an old Xstream 2000 system, so that shouldn't be the problem. Unlike Frank, we haven't had problems with water in the nitrogen from a nitrogen generator. If Frank is correct, that it's water, then either the molecular sieves need to be replaced, or there is ice buildup and blockage in the coldhead. Usually blockage in the coldhead means that you can't get down in temp, or can't maintain it within 1 degree or less. We do bring the temp up, run it at RT over the weekend to dry things out, and then bring it down for routine cooling. If it's turbulence, then you don't have the warm and cold flow rates set correctly. One thing you can see immediately, upon getting down to 100K, is how far is the frosting plume from the tip of the nozzle. If you adjust the flow rates, you can move that plume, caused by turbulence, closer or further from the nozzle. It's also possible that there is something in the nozzle that is causing turbulence no matter what the flow rates are, and your vendor needs to look at that. Bernie Santarsiero ***************************************************** Hi Mark, can you send me a photo of your setup? I would like to see crystal, nozzle, tube and cold head please. I'm sure others will respond as well. Thanks, jim ****************************************************** We have had the same problem and I must admit that the cause is still unknown. The icing issues seem to correlate with the weather, with icing occurring when the humidity is high. One thing that sometimes works is to turn up the flow rate. We run at rates of 60-90 at temperature of -150. John Tanner <tanne...@missouri.edu> Monday - January 12, 2009 2:52 PM ******************************************************** When we initially set up our X-stream with an inverted phi goniometer, there was a huge icing problem, just as you describe. The installer had oriented the cold stream so it was approximately horizontal. When we re-aligned the cold stream so it was blowing upward at angle of roughly 45 deg the problem went away. I speculate that the stream was encountering the lower part of the pin before it encountered the crystal, and that this was leading to some deleterious turbulence (but that's pure speculation). Other comments: We also have a dehumidifier in the lab that's running 24/7. On a few occasions I have (by mistake) left the helium flowing through the focusing optics set at too high a flow rate; this completely ruins the cold stream and leads to massive icing problems. Good luck, Pat Loll ******************************************************** Further to this, one should remove kinds and "low" bends in the tubing, not because moisture accumulates there, but because it's possible that liquid nitrogen accumulates in those spots. If LN2 accumulates it will eventually be enough to block the gas flow in a kind of sputtering action that you will not see, but if the gas flow is blocked even for a fraction of a second, then moist air will collapse towards your crystal. Maybe you should have the engineer lower the cold head on its stand if you need to smooth out the position of the tube. J *********************************************************** Mark, What bothers me about your message is that you already have talked to Rigaku. Until now we have never been able to create a problem that they could not diagnose and help me solve from remote. In danger of offending ccp4 readers: specialized Rigaku experts are a remarkable source for information and solutions, probably better than we are. Your most likely problem is that your nitrogen is not dry? Specifically, check your air dryer (sorry, nitrogen dryer) that it works appropriately. Very specifically, there reside two compressors inside the air dryer and if one no longer works, the quality of your nitrogen stream degrades. It may not be apparent if both compressors work, one can supply all the pressure and volume you need and is sufficiently noisy that you would not notice the second being silent. Of course this problem becomes obvious when you open up the cabinet. (Yes, of course this happened to us once before and in our case the compressor wiring was fickle, as in, working when the cabinet was open and not (always) working when the cabinet was closed; took FOREVER to find the problem.) Your second most likely reason is that the warm stream (outer stream) is not sufficiently protecting your cold stream from humidity, but this is not affected by your phi-axis position. We have two inverted phi-axes and we do not see icing, so there is no fundamental reason why the phi-axis should not be inverted. Mark ************************************************************** Please make sure there is no air vent on the ceiling that is directly blowing air down onto the crystal. Sridhar ************************************************************** Did you try switching the generators over between the two systems, keeping the stream ends the same? It might help to divide and conquer your problem. Whenever we have icing with Oxford systems it seems to come for turbulent flow or poor alignment of the nozzle. Turning off the air conditioning in the room to avoid strong air flows around the instrument can help. Icing never seems to depend on anything supplying the head, as the damn thing blocks with ice in the heat exchanger long before any moisture can get through it. Good luck Jon ************************************************************* Hi I don't think I have much to add, but thought I'd throw this in anyway: 1) As everyone said, get stuff out of the stream. 2) How close to the pin are you? I like it as close as possible without seeing a shadow on the image. 3) Flows. I use a flow lower than reccommended. I like the warm flow to be somewhat larger than the cold flow (35 42). During the summer, the humidity goes up here, so, when that's a problem, I increase the warm flow. What are your flows? 4) Geometry. The flow should hit the crystal first, then the rest of the pin. In other words, you want the nozzle to be on the side of the crystal away from the base of the pin. On an inverted phi, this would mean coming from underneath the crystal. Ensure that the stream passes the base and doesn't get turbulence from that. The only thing either stream should hit is the pin (after it's hit the crystal). Do you use the thin, stainless kind? 5) Our Xstream has a filter bank, which I've been told is on the inside of the cabinet on the generators. Ensure that the first filter (the water separator) is not wet. If there is a lot of water, this will actually vent loudly, so I doubt this is the problem. Even when we had very wet input gas, this cleaned it up nicely and there wasn't a problem at the crystal. 6) Each N2 separator has a vent on the side. You should be able to feel cool gas coming from here. 7) Input pressure to the filter bank should never be < 100 at any point. Perhaps this number is different for you system? Since you have the other system working, 1-4 should have been dealt with. Not sure any of this will be useful. Good Luck. Let us know what happens... Ed _____________________________________ Dr Mark Agacan Scientific Officer, Division of Biological Chemistry and Drug Discovery, Wellcome Trust Biocentre, College of Life Sciences, Dow St., University of Dundee, Dundee, DD1 5EH Tel: +44 1382 388751 Fax: +44 1382 345764 _____________________________________ The University of Dundee is a registered Scottish charity, No: SC015096
