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was purged. Incidentally, several days later, we had a planned power cutoff because of works on the main line and I decided to switch off the microscope completely. I was confident that with the power off there was no risk for the microscope until the problem of condensed water was solved by the engineers. However, several days later, with the system still switched off, we noticed again that the container in the flow meter rack was completely full, this time we could also see water in the transparent tubing going to the microscope. Some tubes are blue so we can’t see through. Now we blocked the compressed air entry to the flow meter rack with a valve but I need advice for the cleaning steps. Te main question is: may I clean the tubes myself or is there a risk that I make a major mistake? And then, if I can do it myself, how should I proceed? What should I be aware of? I have nitrogen and SF6 tanks at my disposal to dry the tubes if it is necessary. Stephane Nizets nizets2@yahoo.com Fri Apr 22 Firstly I feel there is a misunderstanding in relation to the


compressed air and moisture. Moisture, anywhere in the system, is a big problem. Te compressed air when generated or contained in a moist zone will carry the moisture to the control valves which usually have aluminum bases. When an aluminum control valve becomes moist it will oxidize, which ultimately damages the valve and causes an air leak; hissing! How to minimize the damage that your problem may cause? Firstly drain all of the compressed air containers; there should be a tap at the base of each. Now it is down to ideas on cleaning the lines. If it was me I would disconnect the input line to the microscope and blow through the pipes with compressed air from another “dry” source or from as gas bottle (nitrogen would be fine). Cleaning the actuation valves without taking them all apart and blowing though is I think an impossible task. Steve Chapman protrain@emcourses.com Fri Apr 22 Tanks to all who offered their advice. I have unplugged all the


lines and they all contained water, but I am quite sure that the water was lying in the bottom because the system was off so there was no air movement. We’ll probably replace the lines because we are almost sure that the water contained some oil. It is still a mystery why this happened but I don’t want to care about it anymore. In the future we’ll connect an N2 bottle in place of compressed air for the valves. No way that I worry again to waste 600,000 euros worth of material for some stupid moisture (you may replace “stupid” by other not-politically- correct words here, to better reflect my thoughts). Stephane Nizets nizets2@yahoo.com Tue Apr 26 I didn’t chime in on the original question, but I would like to


add my “2 cents” as they say on the general issue of compressed gases. When we designed our new microscopy facility we found a large number of instruments using a large number of compressed air cylinders for valve control and N2 cylinders for vent gas. We then did a cost analysis and found that we could replace all this cylinder usage by a cheaper and easier means. For the compressed air cylinders we designed an air drying system which utilized already clean and compressed dry air from the chemistry building to which we added two large capacity moisture dryers in parallel (so one could be changed while using the other) which happens about every three years or so and also a final activated carbon filter to remove hydrocarbons and a particle filter which gives us extremely dry, HC free compressed air at 110 psi. Tis compressed air is supplied to each instrument’s gallery section to control instrument valves and the air moisture is monitored and connected to an alarm system. For N2 use, this dry clean air is supplied by an analytical grade N2 generation system (from Perkin Elmer) designed for ICP-MS systems so the purity is 99.996% or better with an N2 generation rate of 12 liters per minute. Te unit cost around $15K and uses a membrane filter that


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costs about $100 every 3 years to replace. Tis N2 gas is also supplied to each instrument’s gallery section for use in venting. With these two systems we can supply around 16 different analytical instruments and never buy/rent/haul or connect an air or N2 compressed gas cylinder again. I highly recommend this type of system for both low cost and ease of use. I have to admit, I never liked hauling those cylinders around very much. Te only compressed gases we still buy are a few P-10 and Ar cylinders which are used at very low rates and changed every 6 months to one year or so. Te only caveat I would add is that if you hire contractors to plumb such a system in your lab you should specify “medical grade” plumbing which means they don’t use any fluxes which could contaminate the system. One can also use Silphos solder while flowing N2 gas through the copper (used in refrigeration systems) which is also a fluxless method to prevent flux or scale formation inside the tubing. John Donovan donovan@uoregon.edu Tue Apr 26 I had an IDE air system on a 2010F fill up with water once when


we went too long without purging the compressor. Te replacement system had an automatic purge and an air dryer in series. Be advised that using nitrogen cylinders for valves is ill advised: valve actuators tend to develop leaks over time, and a catastrophic leak could not only deplete your cylinder rapidly, it could fill the room with asphyxiant, which is an unexpected but lethal consequence. Tere were multiple fatalities from nitrogen use when I was at Intel. John Mardinly John. Mardinly@asu.edu Tue Apr 26 My old advisor at Michigan, Wil Bigelow, had a unique and


cost effective method of capturing ultra high purity nitrogen gas for venting microscopes. Tere was an added bonus in that no regulator was required, and it could never overpressurize the chamber and damage ultrathin detector windows. Te cost? Under $20! How? He would put a rubber stopper in the EDX Dewar with a tube in it for attaching a surgical rubber hose that ran to an extra large beach ball. Tat hose was teed to another hose that ran to the microscope vent inlet. A small slit in the surgical rubber hose provided over-pressure protection. Boil-off from the EDX Dewar would fill the beach ball, and that nitrogen would be used to vent the microscope. Te only disadvantage is that some EDX systems have an alarm for sensing low LN2 levels that goes through the fill opening, and that would be difficult to accommodate. I might add that it made the lab look a LOT more cheery and colorful, which was a nice thing to have during the dreary Michigan winters. John Mardinly john.mardinly@asu.edu Tue Apr 26 I have always been cautious with my liquid N2 for the reasons


John raises but have never thought about compressed N2 tanks. In my microtome room, I run 3 N2 tanks to blow off debris from my ultramicrotome knives. It is a lot cheaper and environmentally nicer than using those old compressed Freon cans of gas. Am I really running a serious risk here? It is a relatively big room with an open door into the main lab. Comments? Tom Phillips PhillipsT@missouri. edu Tue Apr 26 John’s post got me thinking too. I am running some valves with


N2 because our CDA (compressed dry Air) supply died three times which crashed the vacuum logic of our 300 mm FIB (bad!). Almost killed a Seiko turbo! Now I am rethinking and maybe will go back to CDA—or install a nitrogen alarm—the problem is the unending supply of nitrogen. Bryan Tracy bryan.tracy@spansion.com Tue Apr 26 In any case, a single bottle is not nearly the hazard that plumbed


in nitrogen is. A. John Mardinly john.mardinly@asu.edu Tue Apr 26 Just a word of caution about using gases in cylinders. We used to use 99.999% nitrogen on our microscopes but discovered water


www.microscopy-today.com • 2011 July


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