the posted query: respondents #1,2

The posted query: What's your experience with compressed air/nitrogen systems? We have been having such trouble lately with our house compressed air that we're going to be getting our own air compressor and dryer. (Piping in dry N2 is not an option for various reasons.) I want to approach this purchase as an informed shopper so we don't replace one bad system with another. If you have your own air dryer or stand-alone compressor/dryer/N2 generator system, I'd like to know what it is and how you like it. (If you don't have such a system, but have relevant thoughts on the subject of dry compressed air, please share them.) Specifically, I'd like to know about: A) Compressor reliability. What happens if your compressor fails? Is it a "dual" unit? Do you have a separate backup compressor? B) Dryer reliability. Do you have a backup dryer, and if so, how does it get switched on? C) Air quality monitoring. Do you have a dew point meter? How dry is your air? Do you monitor pressure? D) Siting & vibration. How far away is your compressor from the spectrometers? Do you have any special mounts to isolate the compressor's vibration from the floor? What measures have been taken to keep the compressor's acoustic noise down? E) Brand recommendations. Please tell me what brands of equipment you're using in your discussion, and whether you'd recommend them to me or dissuade me from them. We're looking at equipment from Quincy, Atlas/Copco and Ingersoll-Rand.

Respondents #1,2

(1st of three entries) Bottom line, be sure to choose a compressor that can handle the total flow of your instruments, PLUS any air dryers and (should you choose to buy one) an N2 generator. We had to install our own compressed air system in our 800MHz facility, and it turned out to be a huge headache. The engineers sized everything based upon the typical and maximum flow requirements for the spectrometer itself, which is negligible (unless you need to do MAS-solids, which we don't on that instrument). The entire NMR spectrometer system averages 1.05 CFM of air flow, including the console and the magnet legs (which are mostly static pressure). The problem is that we also have a twin-tower -65 Deg.F. (dewpoint) dessicant dryer (Parker/Balston), and a Parker model HFX-3 N2 Generator sized to give ~90%-95% pure N2 (installed after the filters and the dryer). Our engineers thought they had taken the flow requirements of the dryer and N2 generator into account; however, they were WAY off. We initially installed a 5HP Dual reciprocating compressor, with a 120gallon ballast. It was supposed to run at a ~25% duty cycle, and it was running at near 100%! After a lot of measurements, we discovered that the combination of the desiccant dryer and the N2 generator were increasing our flow requirements to ~11-12 CFM, which equaled the maximum output of our reciprocating

compressor. These things will burn themselves up if they are running at greater than 50% duty cycle for extended periods of time (and they are LOUD). After more testing, we determined that the Air Dryer was adding 4-5 CFM to the total flow, and the N2 generator was adding an additional 6-7 CFM. We replaced the reciprocating compressor with a Kaiser Screw-type compressor that could easily handle the 10-12CFM load, and we kept our 120 Gallon ballast to act as a buffer. This air has an auto-drain, and goes through a refrigerated dryer before going to our Balston filters (Both BX and DX grade), the dessicant dryer, then through the N2 generator. Screw compressors are designed to run (almost) continuously, and are very quiet. We haven't had any problems since installing this configuration. One additional issue that we have found to be very important is to have a good-sized ballast down stream of the dryer. As these cycle between the towers, there is a fluctuation in pressure. We have the final output of our purified N2 dumping into a 60-gallon ballast tank (with a pressure gauge, and a pressure sensor connected to a sensaphone alarm system), then it goes to the spectrometer. We have very smooth, continuous pressure using this setup. This may be more information than you wanted, but this issue occupied nearly 6-8 months of our lives, and I wouldn't want to repeat the mistakes that were made.

(2nd of three entries) I realized that I didn't answer your specific question in my previous message. You might get these answers from my colleague, XXXX, so simply ignore this if it is duplicate information from ZZZZZ. A) We use a Kaiser Screw compressor (I can get the model number, but it's rated at 12 CFM continuous. We do have a backup system, which is the building air. The building air has proved unreliable as a primary source, but is adequate as a backup. The building air pressure is slightly low for us (too low for the requirements of the Varian Cold-Probe pneumatics and the 800 Magnet legs); however, we have a separate backup specifically for the static pressure requirements of the magnet legs and cold-probe CCC valves. A very small, silent compressor provides 24/7 backup (using a series of check-valves) for our high-pressure air for these specific devices. I have pictures of this cold-probe/magnet-leg backup system if your are interested. B) The Parker/Balston dryers are extremely reliable (we have 3 of them throughout our facility), and we've never had a failure. We replaced one after 15 years of service because some of the air connections were leaking, cracked, and worn out. However, it performed well (based on the lack of

icing in the FTS chillers) to the very end. C) We do not have any monitoring of our final purified N2. We looked into dewpoint/humidity meters, but they were very expensive. Based on the specs of our dessicant dryer and N2 generator, we should have about 98% pure N2 with a dewpoint well below -80 Deg.C. We periodically check the FTS chiller for icing, and have never seen any sign of condensation in the FTS chiller. We DO monitor pressure, using a passive, mechanical pressure "switch" (the kind used to cycle compressor motors on/off), and a sensaphone monitor, if the pressure drops below ~80PSI, the sensaphone unit starts dialing phone numbers until someone acknowledges the problem. We use sensaphones to monitor water/flood, lab temperature, the 800 magnet pumping system, air pressure, ... pretty much everything. D) So far our Kaiser compressor has been extremely reliable, but that doesn't help with your comparative analysis vs. other brands. The hassle with the Kaiser is the frequency of oil changes and filter changes, which is a rather messy business (but not too difficult).

(3rd of three entries) Having gone through this with our 800, I can give you some thoughts which may be helpful. If you decide to post a summary, you'll have to prune this, but a full description is probably most useful. Also, you didn't mention what sort of systems you need air for - my setup is for liquids NMR on a single instrument (although I think we could run 2-3 no problem), but if you do MAS solids you'll need quite a bit more flow. We have an air compressor -> ballast tank -> refrigerated dryer (-40 dewpoint) -> Ballston "tower" type dryer (-100 dewpoint) -> N2 generator (passive/membrane type) -> ballast tank -> air manifold -> magnet. We get >97% N2 with virtually no water. Initially, our main source of compressed air was a pair of Sullair screw compressors, but they have had their output pressure reduced (now barely what we need) and they are severely underloaded and could die or be shut off at any point, so they are now our primary backup system (a check valve keeps us off this system unless our main fails). In "replacing" the Sullairs, we first tried to use a twin reciprocating air compressor. It never worked adequately, and here's the main thing I think you need to look out for. The combination tower dryer + N2 generator we use cause a loss of >10 CFM worth of flow. Although the instrument really only needs 1-2 CFM most of the time, the recip system maxed out right around 12 CFM running >80% duty cycle with both motors in tandem. It kept blowing fuses and/or overheating. In the end, we replaced the recip unit with a dedicated screw compressor (Kaeser SX-6). This unit is designed to run at near 100% duty cycle and puts out ~15 CFM at 110-120 psi, which gives us >90 psi dry N2. It's also smaller and MUCH quieter than the recip unit was. It also doesn't vibrate all that much, although it's located in a different room >100' away from the magnet. It does require service every 3-4 months (oil and filter changes every 3000 hours) with a quick weekly check of an air filter

sort of similar to a furnace filter. The service is messy and takes about 1/2 day, but otherwise I've got no complaints whatsoever about this unit. You might need to go one size up for multiple instruments. It's a little noisy to keep in the same room with the magnet (I think the rating is 60-70 dB, you don't have to shout over it or anything), but it's quiet enough for any sort of utility/mechanical area or possibly loading dock. You also asked about backups. First, we have no formal backup for the air dryer, but with the refrigerated dryer + tower dryer even if one goes we should always have air at a -40 dewpoint or better. For the air compressor, our backup is comprised of a pair of compressors. The main supply is an older Powerex scroll compressor (which we already had lying around) that pipes into the same first ballast tank as the Kaeser screw compressor - it's set to run between about 70 and 90 psi, so it's internal pressure switch keeps it off unless needed. It is rated for 115 psi but unhappy with any significant duty cycle over 90 psi. This keeps us at 60-70 psi out of the N2 generator and backs up our lower pressure but higher flow systems (VT, eject, spin, etc.). For the high pressure requirements (currently the legs, but eventually also the pneumatics for a cold probe) which have very low flow requirements, we purchased a 6 gallon pancake type "Panther" compressor from Werther Intl. It does up to 120 psi max pressure (set at ~90 psi) and is VERY quiet (~40 dB). This sits right below our air manifold and a pair of check valves keep it isolated to only the legs and only if we don't have enough main pressure. I highly recommend this unit, although it does cost ~$1k.

Respondent #3 Running a compressor is a pain in the ass. We have some compressed air from a cylinder piped in through a check valve to back us up during short outages or pressure drops, without supplying the whole building. This is particularly important with cold probes, which effectively require uninterruptible compressed air. We have a Hankinson 10 scfm regenerating desiccant dryer, and these have proved to be very reliable provided you keep water and oil away from the desiccant. In addition to the filters supplied with the dryer, we have a large industrial steam trap in front of the dryer to catch really big slugs of water. The desiccant columns can be changed if they get contaminated--it takes about half an hour to replace the alumina pellets. Bruker supplies a passive nitrogen separator device that is sufficient to purify the normal VT gas supply flow to ca. 98% nitrogen. They susceptibility match their probes >= 500 MHz to nitrogen so this is important. As far as I know, Varian probes are all susceptibility matched to air, and may show diminished susceptibility cancellation if run with pure nitrogen.

Respondent #4 We have three nmrs in operating. All of them are hooked with mechanical air compressors since they were installed. The oldest Bruker DPX400 has been operated since 1995. The compressor is without Brand name. The others, Varian AS500 and AS400 were installed on 1999. The compressor is JUNAIR and the dryer is WILKERSON. Simple maintenance are needed in regularly, such as replace air filters. A

cylinder heads were replaced last year. We don't have Nitrogen generator. We will order a Nitrogen cylinder when it is needed for VT experiments. Nitrogen usage is low demand for us.

Respondent #5 Last year we put in a dry N2 system based on a compressor/air dryer/N2 PSA unit for our instruments. It handles a LCMS system and a liquids, a liquids-solids and a full solids NMR spectrometer facility. The compressor/air dryer is a Kaeser and is fairly quite. It requires a bit of periodic maintenance but that can be completed in about an hour. In addition we have a PSA Nitrogen generator that is fairly small for the volume of air it handles. At the end of all this is a 300 gallon ballast tank to reduce pressure and flow drops during periods of high load. Air quality is measured at the membrane system. We get 99.4 % N2 out at -90 C dew point. We can do VT down to -90 C with this air. The unit is located in our basement, one floor down. There are significant vibrations, noise and heat. I wouldn't have them near the instruments. The compressor, N2 system and other components have been very reliable. We have a local rep for compressor repairs. The other components will not need much in the way of maintenance if the front end is in good condition. We have a I-R compressor built into our Liquid N2 plant. It has had it's problems over the years. I feel the Kaeser is a much better built piece of machinery. Specifics on what we have are: Here is the information on our N2 system. Kaeser SM-11 simplex package (10 HP rotary screw compressor with refrigerated air dryer). Beko model DM20N48C-A Membrane air dryer with high efficiency coalescing pre-filter and auto drain On Site Gas System N-50 Nitrogen Generator (PSA system rated at 657 SCFH at 99% N2 with input air pressure at 100 psi) The air compressor is set to a pressure of 175 psi. It is meant to produce 36 SCFM at 150 psi. The system has been set to produce enough N2 for the three magnets and the LCMS at ~99.5% N2 purity. The Beko system is used as a filter to reduce the moisture in the air after the refrigerated air dryer.

The N2 generator runs off of a 115V line. The air compressor must be run off of a 230 or 480V 3-phase line. Although the air compressor comes with a 80 gallon tank we've installed a 120 gallon receiving tank after the N2 generator. All of the components were purchased through On Site Gas Systems.

Respondent #6 When we bought our first 300 in 1990, we also bought a Balston Air Filter/Dryer; we used our house air for input to this device. During the first fifteen years with this the dryer needed servicing only once for some gaskets that needed replacing. This has been so effective that when we moved to a new Science Center and bought a new 500, the filter/dryer was simply moved to the new building, with continuing terrific service. Balston used to be in Rochester, but they've been bought out by Parker in Haverhill, MA. The Parker people were very helpful when we had to replace those parts a couple years ago. The filter/dryer has required no attention other than that in the last sixteen years. We''re running at about 80 psi to keep all the vibration dampers up to snuff, and we use the "nitrogen separator" provided by Bruker for the spinner (although we seldom spin any samples any more). I think we paid about $2500 for the thing. It just fastens to the wall. I checked their web site (you can get to it by Googling Balston) and found the same model (#75-20) as we've got, so they are still selling this. It does make some noise as it cycles from drying tower to drying tower, and that can be a little unnerving to the real beginners, but one quickly gets used to it. So, for us, this has been a terrific way to go.

Respondent #7 I have Air dryer/filter from Parker Balston change filters every year or so. Has indicator for water. Self-regenerating dessicant. No issues. I suggest for a compressor look into scroll pumps. Quieter than other tech pumps and no real issue with oil. Need to change seal once a year is only maint.

Respondent #8 Josh--look around for an old Balston compressor/drier or a new one. Surely your place has compressed air available so the Balston can be used as an "air conditioner" if you only use it for drying and CO2 removal. That's what we do for our Avance 400 and prior to that with our AC 300 with no problems whatsoever.

Respondent #9 We have only one AV 300 machine with a old model oilfree air compressor (piston mode with 2 hp engine) which is recently started under producing. Although I am interested to go for a new one and possibly a scroll type this time but, I am not sure about the longevity and trustworthyness of this new system technique. Hence, I request you to forward me the replies that you get as a response to your new posting in the AMMRL. Also, I request your views, if any, about Scroll type Air Compressors.

Respondent #10 Just a few thoughts - I can't give too many technical specs off the top of my head (and they probably wouldn't be appropriate to the US anyway), but we've had a few issues with our systems that might help your thought processes. A) Reliability - We run a 'dual' system. This has been great in terms of reliability of air supply, but we've had all sorts of problems with the control system - so often the pair of compressors have not switched. Fortunately this has not coincided with a compressor failure. Currently both are running together and the control system has not switched one off - we have no idea why, but again it's not affecting supply, so we are waiting for an engineer to have a look at the control box (AGAIN!). B) Dryers - we don't believe you can ever have enough. We have a main dryer on the tank, but have added in-line drying after the tank to ensure dryness. We are about to upgrade these in-line dryers to diaphragm dryers, but essentially we have double redundancy in our drying to make sure we never need to worry about this. On instruments running low temperature experiments we add in-line dessicant beads (freshly activated) to the line whenever these experiments are run (about 1-2/week). C) Quality - We don't monitor the air moisture except on one instrument (600MHz) as it's not utterly crucial. Our biggest concern is oil/particulates, so we have doubly redundant oil filters as well. D) Our compressors are in an adjacent plant room - about 30 feet from the nearest spectrometer. They are on plniths, but otherwise no effort to damp vibrations is made. We are in the basement and have no problems with vibrations on our undamped lower field spectrometers (270-500).

Respondent #11 We run two High-Res Bruker spectrometers running 24-7 in automation using autosamplers from one dedicated Jun-Air compressor 4000-150BD3. We also run a solid-state MAS spectrometer from a separate dedicated Jun-Air 4000-150DB3. These are oil-free compressors.

A) Compressor reliability. > What happens if your compressor fails? Serviced anually - no problems yet.... The auto sampler stops and the MAS switches off in a controlled way. Students complain that their spectra are not available.

Do you have a separate backup compressor? No

B) Dryer reliability. Do you have a backup dryer, and if so, how does it get switched on? Air is dried automatically by a unit on the side of the compressor prior to storage in the pressure vessel.

C) Air quality monitoring. Do you have a dew point meter? How dry is your air? Do you monitor pressure?

Expansion of bearing and rotation gas flows within the MAS unit have not caused a problem....yet, that said, we have not tried MAS at "low" temperature. The temperature range -90'C to +120'C is OK for the HighRes spectrometers

D) Siting & vibration. How far away is your compressor from the spectrometers? Do you have any special mounts to isolate the compressor's vibration from the floor? What measures have been taken to keep the compressor's acoustic noise down?

Spectrometers are on the 1st and 2nd floors, compressors are in the basement. MAS required 2.5 inch pipe work from the compressor to the spectrometer to maintain required pressure and flow rate. Compressors sit on rubber feet and are on a concrete floor and are so far away that vibration is not a problem.

E) Brand recommendations. Please tell me what brands of equipment you're using in your discussion, and whether you'd recommend them to me or dissuade me from them. We're looking at equipment from Quincy, Atlas/Copco and Ingersoll-Rand.

Our Atlas Copco compressor died a horrible death some years ago and repair was very expensive and a new compressor with service contract was unecconomical.

Respondent #12 for SS-NMR we use two scroll compressor ( possibility of one master and a slave or tandem with delayed start) these generate a lot of (compression) heat and require well ventilated technical room but newer screw with catalytic oxydation of oil would probably be more reliable and pollution free. They wear out after; 2/3 years Their nominal flux is limited by the Iwata patented design and you may just choose between two choices depending on Pmax Air dryer by recycling zeolithe colums can provide dew point down to -80°C if you accept frequent recycling i.e. 30-40% loss of flux for the application itself Filters remain clean for ages with oil free compressor systems balast down stream buffers P fluctuations. Avoid oil and filter duties as much as possible Check that all is clean during instal and before starting ( here downstream of the oil free compressor they had installed an oiled/waxed non SS steel Balast reservoir !!!) Teflon or SS piping is betteragainst moisture uptake A colleague at Material science dept uses N2 to eliminate O2 paramagnetic ? having plenty of dry air can be convenient ( here for glove box in dry conditions i.e. ionic liquids)

Respondent #13 I have one Avance 400 and the compressed air comes from far away in our building. We have two cascaded driers/traps and I have never seen any water in 15 years. Now we have a new Avance 600 much closer to the compressor with a single trap. It fills with water in about 3 weeks. I am quite disgusted and I plan to move at least one drier

from the 400 to the 600. The 600 uses a "nitrogen separator" fed with high (5 bar) pressure air. Both instruments have pneumatic antivibration mounts. Thus far we have not needed anything more than this.

Respondent #14 I run an old AC300 in what could be considered 3rd world conditions so I thought I'd chime in to give you some data on harsher environments. I use a small compressor bought from Home Depot with a simple dryer attachment. My console and magnet are in ambient conditions - the room is a well ventilated lab but with no air conditioning. On Sep 26, 2006, at 6:13 PM, Josh Kurutz wrote:

A) Compressor reliability. What happens if your compressor fails? Is it a "dual" unit? Do you have a separate backup compressor?

I have not had a problem so far with the small unit I purchased. I'm in very humid conditions, so I drain the air tank every few weeks as some water collects there. If the air intake is in a dry/air conditioned area it'll probably need some draining but perhaps not for long periods. I guess the back up is running back to Home Depot. They have several sizes and I'm sure the larger ones could handle several consoles.

B) Dryer reliability. Do you have a backup dryer, and if so, how does it get switched on? The dryer is not chemical based on my unit - its a simple droplet trap. I have had zero trouble with the spinner - but thats on an Oxford family style magnet.


The air is probably fairly wet. I imagine its not as wet as ambient., but I don't check it. The pressure is set at the compressor and fed into the control unit.


M y compressor is about 7 feet from the magnet. It only cycles when I eject or spin. If I spin the compressor cycles on and off every minute or so. Its fairly quiet, however a large unit would be pretty loud so I'ld put it in a closet or adjacent room.


I'm using Home Depot's "Husky" brand - its the smallest one that looks like a carry-on suitcase. Just thought I'd give you an example of the "low end" situation.

Respondent #15 I have similar problems at UXXX. Rather than dropping off the building air, I'm taking a note from S's book and putting in a check valve with my compressor. That way the compressor only picks up load, when it is needed (when building air goes down). I bought a cheap compressor from Grainger, but it doesn't have and auto-drain. The vendors, you mentioned, are good options. I have an old Balston regenerative air dryer, that I'm going to use for one of my labs and I'm in the process of buying a Hankison DHW-10 for drying and a nitrogen separator for N2 to the bore of my Brukers. Both are regenerative dryers with drains on coalescing filters before the drying beds. Back in Kansas, one lab had a Hankison that worked well. I made sure to drain any coalesced liquid weekly during the summers. That dryer is about 15 years old, with no problems when I left. Our dew points were about -40 C. To change to a -100 C dew point implies a shorter cycle time on this type of dryer. There is a drop of pressure 3-5 psi across the dryer and 1-2 across the N2 separator. Currently the air for my lab is using the membrane filter on the building air (dew point 10 C), so I use house N2 for bore air on all the magnets (Varian and Bruker).

Respondent #16 This is something with which I *do* have some experience. We have been fortunate to have our own dedicated air compressor, and when we relocated, this was one of our primary requirements for the new space we moved into. You should not be using house air. In addition to your own dedicated compressor (with backup) ideally, you should have a -100C pressure-swing absorption air dryer. The compressor system we have in our new space is made by Beacon Medaes (www.beaconmedaes.com) -- it is a duplex unit oil-less scroll compressor (www.beaconmedaes.com/medicalAir/scroll.html) I very highly recommend it! It has many advantages -- the scroll compressor does not create a lot of vibration, although their advertising of "low noise" is a relative term (I would not want to be in the same room with the compressor). The fact that it is oil-free means that one of the worst kinds (for NMR) of compressor failure is not possible, i.e. there is no chance that it will fail in such a way as to send gobs of oil up the air line, ruining your air-dryer, or worse, your spectrometer. And finally, it comes standard in a "cycling" dual backup configuration -- it has two (or more) compressor modules, and automatically switches between the two to keep the operating hours equalized over time. These units are primarily meant for hospitals, where I suppose if the compressed air goes out someone could die, and as such are very reliable for NMR use. The units we bought came with a built-in -40C air-dryer (with electronic monitoring) which we had swapped out to use a -100C air-dryer made by Zeks. If you never went to low temperatures (i.e. stayed above 0C, or took other precautions such as using nitrogen in these cases) you might even be able to get away with the standard air dryer on these units. We have been running with this setup for a couple of years with

absolutely no problems!

Respondent #17 Our system consists of a [Atlas]-Copco SF4 (full feature with internal air drier), a Balston air drier which provides air with a dewpoint around -50 and a receiving tank. A cylinder of compressed nitrogen is included in the system, with the regulator set just below the low pressure setpoint of the compressor, as short term backup in case of compressor failure. In the case of compressor failure, we can switch to the rather wet house compressed air. This feeds four spectrometers, all Bruker Avance (400, 500, 600 and 700 MHz). The 400 and 700 are solids capable, and we also use our compressed air for MAS. The 500 and 700 are equiped with Cryoprobes, and the compressed air is also used for the Cryoplatforms associated with them. All instruments have BCU05 cooling units. All except the 400 have N2 seperation cartridges (Sumitomo) to provide ca 98% N2 to the probes.

B) Dryer reliability. Do you have a backup dryer, and if so, how does it get switched on? The internal drier and external drier can be used alone or together. The internal drier provides a dewpoint of around 5C, which is good enough for most of our work (being a biochemistry facility, we do very little work at low temperatures). If we need air of a lower dewpoint, both driers are used in series. The amount of air required to operate the Balston unit is quite high - when it is in use, the SF4 runs at least 90% of the time, with only in internal drier in use, the SF5 runs about 55% of the time.


We have a dew point meter in the compressor itself (after the internal air drier) and a cartridge after the Balston unit that changes colour when the dewpoint is near -50. We have pressure gauges at the compressor itself, at the receiving tank, and in each room where the spectrometers are located (the four instruments are in three different rooms, all on the same floor). We maintain the pressure between 80 and 100 psi (the cryoplatforms require about 70 psi which is the limiting factor).


The compressor is located in a room across the hall from the room containing the 400 and 500 MHz spectrometers on rubber supports to damp vibrations. The noise when the compressor is operation is not excessive and cannot be heard outside the room where it is located.


We chose Atlas Copco based on the recommendation of Bruker. The first unit we got was a lemon, giving us many problems and after a couple of years the scroll element was destroyed beyond repair. They replaced the unit for us at no charge a couple of years ago and since then we have had no problems at all aside from

routine replacement of the belts and seal tip on the scroll element (done once so far, after 10,000 hours of operation). Nots that as delievered, the internal air drier is not connected on these units.

Respondent #18 Having gone through this with our 800, I can give you some thoughts which may be helpful. If you decide to post a summary, you'll have to prune this, but a full description is probably most useful. Also, you didn't mention what sort of systems you need air for - my setup is for liquids NMR on a single instrument (although I think we could run 2-3 no problem), but if you do MAS solids you'll need quite a bit more flow. We have an air compressor -> ballast tank -> refrigerated dryer (-40 dewpoint) -> Ballston "tower" type dryer (-100 dewpoint) -> N2 generator (passive/membrane type) -> ballast tank -> air manifold -> magnet. We get >97% N2 with virtually no water. Initially, our main source of compressed air was a pair of Sullair screw compressors, but they have had their output pressure reduced (now barely what we need) and they are severely underloaded and could die or be shut off at any point, so they are now our primary backup system (a check valve keeps us off this system unless our main fails). In "replacing" the Sullairs, we first tried to use a twin reciprocating air compressor. It never worked adequately, and here's the main thing I think you need to look out for. The combination tower dryer + N2 generator we use cause a loss of >10 CFM worth of flow. Although the instrument really only needs 1-2 CFM most of the time, the recip system maxed out right around 12 CFM running >80% duty cycle with both motors in tandem. It kept blowing fuses and/or overheating. In the end, we replaced the recip unit with a dedicated screw compressor (Kaeser SX-6). This unit is designed to run at near 100% duty cycle and puts out ~15 CFM at 110-120 psi, which gives us >90 psi dry N2. It's also smaller and MUCH quieter than the recip unit was. It also doesn't vibrate all that much, although it's located in a different room >100' away from the magnet. It does require service every 3-4 months (oil and filter changes every 3000 hours) with a quick weekly check of an air filter sort of similar to a furnace filter. The service is messy and takes about 1/2 day, but otherwise I've got no complaints whatsoever about this unit. You might need to go one size up for multiple instruments. It's a little noisy to keep in the same room with the magnet (I think the rating is 60-70 dB, you don't have to shout over it or anything), but it's quiet enough for any sort of utility/mechanical area or possibly loading dock. You also asked about backups. First, we have no formal backup for the air dryer, but with the refrigerated dryer + tower dryer even if one goes we should always have air at a -40 dewpoint or better. For the air compressor, our backup is comprised of a pair of compressors. The main supply is an older Powerex scroll compressor (which we already had lying around) that pipes into the same first ballast tank as the Kaeser screw compressor - it's set to run between about 70 and 90 psi, so it's internal pressure switch keeps it off unless needed. It is rated for 115 psi but unhappy with any significant duty cycle over 90 psi. This keeps us at 60-70 psi out of the N2 generator and backs up our lower pressure but higher flow systems (VT, eject, spin, etc.). For the high pressure requirements (currently the legs, but eventually also the pneumatics for a cold probe) which have very low flow requirements, we

purchased a 6 gallon pancake type "Panther" compressor from Werther Intl. It does up to 120 psi max pressure (set at ~90 psi) and is VERY quiet (~40 dB). This sits right below our air manifold and a pair of check valves keep it isolated to only the legs and only if we don't have enough main pressure. I highly recommend this unit, although it does cost ~$1k.

Respondent #19 If the building compressed air supply has insufficient pressure, capacity (in scfm), or reliability, there are air compressors available which are much quieter and which produce much less vibration than the standard reciprocating style used in industrial settings. When we discovered that our building's compressed air supply would not be sufficient for MAS experiments and that there was no space available for installing a dedicated air compressor except within the NMR lab itself, I did some research and found that rotary scroll air compressors were a viable solution. Our compressors come from a company called Powerex: http://www.powerexinc.com/index.asp?fuseaction=productDetails&product_subcategory_id=24 We originally had the 3 HP three-phase model but then later upgraded to a 5 HP three-phase unit. These compressors are very quiet and use no oil, which simplifies the filtering equipment which must be installed between the compressor and the spectrometer console. They are very reliable and require little maintenance. I wrote two articles for the now-defunct Texas A&M University (TAMU) NMR Newsletter describing the complete system we built, including the Powerex rotary scroll compressors, which I have attached to this E-mail as Word files. If they aren't readable, let me know and I can FAX them. We bought our air compressors along with a 30 gallon buffer tank from Craig Mazzatenta of LBS Corporation: http://www.lbscorporation.com/contact.htm Regardless of whether compressed air comes from a building-wide supply or from a dedicated compressor, condensate separation and filtration are always required to prevent water, oil vapor and metal dust from entering the spectrometer console. This is particularly true for building compressed air supplies, since these often are laden with oil droplets and rust particles. We feed compressed air from either the building supply or from our Powerex compressor into a 30 gallon buffer tank, where some water condenses and is drained from the bottom of the tank. Next, air enters a refrigerated drier in which the air is cooled to about 32 F, separating more water from the supply. Replaceable porous filter elements remove any debris larger than 5 microns. Finer filtration (1 micron or smaller) is needed for MAS experiments. For low temperature applications, a dew point lower than 32 F is needed to prevent ice formation. This can be achieved by passing the air through a self-regenerating desiccant drier, which reduces the dew point to about -100 F. The condensate separation and drying apparatus is described in detail in the attached files. An alternative to the above is to use liquid nitrogen boil-off to operate the console. This involves the use of refillable liquid nitrogen "gas packs", dewars with built-in heat exchangers to build up the required vapor pressure above a bath of liquid nitrogen. These gas packs produce gas with an extremely low dew point free from oil vapor. Filters are needed to remove ice particles, but no water separation equipment is needed. A typical gas pack (Taylor-Wharton XL-70) holds 265 liters of liquid nitrogen and delivers 125 psig for up to 16.8 hours at a flow rate of 350 scfh (5.8 sfcm); obviously, lower flow rates will allow longer operation times. For instance, during normal operation (not ejecting), one might use gas at a flow rate of 57 scfh. This flow rate could be maintained with a 265

liter tank for 103 hours. This is an attractive solution if you have ready access to liquid nitrogen and someone to refill the tank periodically. Note that full tanks are very heavy (up to 900 lbs) but can be handled by one person using an appropriate cylinder cart. Having two or more tanks connected to a gas manifold is highly advisable if funding and space are available.

Respondent #20 Here is my $.02: My blood pressure has dropped considerably since we went off house air and onto our own supply. We had similar problems to yours with house air (water, gunk, unreliability ...). We now have an overkill system of two Atlas/Copco gx2-ff compressors with integrated refrigerating dryers. We could probably get by with half this capacity. They automatically switch roles every 100 hours. I haven't checked to see where the dryers were set, but the spec was for -60F. We've had two minor glitches with the compressors in one year. This was no problem because of the redundancy. If we'd only had one compressor head things would have been ugly. I don't really think that you need two separate compressors and two tanks. A single tank w/ two heads could be just as reliable. Right now we're monitoring pressure via webcam, but we'll install sensors sometime this fall. One of the sensors is a moisture meter, and we will also have a moisture sensor on a nitrogen separator when that comes in mid-November (BTW, we chose sieves over a membrane for the separator.) The compressors are in a room about 35' from the center of our 800 magnet, but not on the same floor structure as the magnet area. The compressors are on steel stands to give us about 3' of storage underneath. The compressors are in an enclosed room with heavy doors. One suggestion I would make is to use acoustic-damping sheet rock and fiberglass insulation in the walls around the compressor. We didn't and it was a mistake. Easily overlooked is that a drain must be available for the water that runs out of the dryers.

Respondent #21 A) Compressor reliability. What happens if your compressor fails? Is it a "dual" unit? Do you have a separate backup compressor? No backup for compressor. Spinning stops when power goes off. Dryer is dual column. B) Dryer reliability. Do you have a backup dryer, and if so, how does it get switched on? No backup for dryer. C) Air quality monitoring. Do you have a dew point meter? How dry is your air? Do you monitor pressure? Have never tested the dew point. Wall gauges near magnet show pressure. D) Siting & vibration. How far away is your compressor from the spectrometers? Do you have any special mounts to isolate the compressor's vibration from the floor? What measures have been taken to keep the compressor's acoustic noise down? Quiet compressor, NMR on 3rd floor, compressor on concrete on earth on 1st floor, vibration therefore not an issue. E) Brand recommendations. Please tell me what brands of equipment you're using in your discussion, and whether you'd recommend them to me or dissuade me from them. We're looking at equipment

from Quincy, Atlas/Copco and Ingersoll-Rand. Atlas Copco SF 2, lifetime = 5 years, needs special grease, absolute requirement for belt & filter change which I leave to our Physical Plant, think is once a year. Our Physical Plant people say they check it once a week. Two years old now, trouble free. Must be on continuously so Hankison dryer can dry itself. Hankison DHW-10 Wall Mount Air Dryer, Al2O3, 2 columns, self-drying. 60 Gallon ballast after Hankison Air Dryer. I highly recommend this system. I had a terrible time choosing it, even with AMMRL, because our very competent Physical Plant couldn't help me since they really didn't know what an NMR is. Half baked web sites. There are no compressors designated for NMR. Alot of dentist office stuff. Mixed up sales people. I really went out on a limb two years ago. Good luck.

Respondent #22 We have our own air system in one building with several NMRs, but use the house air where there are only one or two liquids spectrometers. That's not to say we use the house air as delivered. We run it through separators, filters and a dryer before using it. You didn't say whether your problem with house air is quality or quantity (or both). If there is a reliable quantity, and there are only one or two spectrometers, I recommend treating the house air, because you avoid the continual maintenance of your own compressor. If you have a solids machine, then you might need your own compressor even if it's the only NMR in the building. We have backup compressors and dryers in only one bulding where there are many spectrometers. We simply use the several old worn-out Ingersoll-Rand compressors and refrigerated dryers that were used in the past as primary sources. They are quasi-automated by setting the turn-on pressures barely lower than that of the primary unit. I see the issue of backups as a choice between getting uninterrupted operation, or getting fairly reliable operation while avoiding damage during outages. I can provide a minimal backup supply for little cost, providing enough air for probe/shim cooling until the NMR can be shut down. Otherwise, to provide uninterruptable operation, one must spend a considerable amount to install complete full-load redundancy. The way I look at it, the cost of replacing a probe and highly labelled sample might be $5,000 to $20,000, but if I have reliable equipment and keep it maintained, the odds are very rare that will even happen. If I buy total redundancy, the cost is no longer a rare maybe - it is now certain. Plus there is much greater up-front cost than I could lose in the worst case, and there is added maintenance of the redundant systems. Maintenance is one thing to look at carefully. The more specialized the compressor, the more specialized the maintenance. Stick to a normal oiled unit and then remove the oil and water. The dry lubricated designs are way too much maintenance, plus added initial cost for exotic technology. If you

or other staff are not mechanically inclined, then you should budget for a service contract. In fact, you might avoid the new compressor issue altogether by buying a service contract for the house compressor. That brings up the issue of support. Don't buy a compressor from a distributor that is not located near you. Buy whatever brand a local, warranty-servicing dealer specializes in, if you can. Our equipment is mostly Kaeser. We use their screw compressors and recirculating dual tower dessicant dryers. The quality is very good, but there is some more maintenance than a conventional compressor. The Kaeser compressors are a belt-driven screw (just like a supercharger on a car) with an integral oil separator. This design has many fewer moving parts than a reciprocating piston, so it is more reliable. On the other hand, it is German, so maintenance parts are more expensive. After our compressors, we have an oil/water coalescing filter, a carbon filter, and a particulate filter before the receiver tank. The dryer comes after the receiver, then a particulate filter and another carbon filter. On house air, I use virtually the same setup. The receiver tank and coalescing filters have timed blow-off valves to drain accumulation. The systems are monitored/maintained weekly. I would avoid refrigeration dryers, because they have reliability and lifetime issues inherent in their mechanical design. Dual-tower, recirculating, dessicant dryers are the way to go. The technology is simple, maintenance costs are low, and lifetime is indefinite. Balston and Kaeser are the brands we have, and both are good. If a refrigerated dryer has a problem, the sealed, non-repairable compressor inside necessitates complete replacement. If a dessicant dryer fails, the offending solenoid or the dessicant can easily be replaced with generic brand parts. Commonly, the dryer has a salt-color indicator to tell if it is working, but they change color at positive dewpoints, after the moisture is already too high for NMR. Mostly they just verify what we already know from the water accumulating in the filter bowl at the spectrometer, or the unexpected water peaks in spectra. I looked into dewpoint measurement and found 3 basic approaches, each with drawbacks. Ultimately, I decided to ignore the dewpoint issue because we always use N2 gas for VT work, and the spectrometers always give us an indication of a dryer problem before anything is damaged. One type of sensor measures dewpoint from a weather perspective; these have no resolution for negative dewpoints, and so are not suitable for NMR. Another type precisely measures negative dewpoints at atmospheric pressure; these require a bleed from the air system which adds load, and the mathematical conversion needed to compare the spectrometer specs requires additional temperature measurements. If you simply want to monitor the condition of the air relative to your own arbitrary standard, then these

sensors will work fine. They are relatively inexpensive (<< $1,000). I recommend Omega brand. If you want to measure the dewpoint at pressure, like the spectrometers are spec'd, then a more expensive, state-of-the-art sensor is needed (>$1,000). These are typically temperature and pressure compensated, and mounted in a pressure-rated fitting. I recommend Valhalla brand. The latter 2 types don't necessarily come with a power supply or readout, so additional equipment is needed to operate and monitor them. N2 gas for VT work is plumbed through one building, originating at the large outdoor LN2 supply. In this building we have an automatic air/N2 switch on each spectrometer. If air pressure drops off, the N2 takes over. N2 is manually selectable for VT. In buildings without N2 plumbed in, we use LN2 supply dewars configured as gas-packs for VT. If needed, we can connect several to a header. When no VT is planned, they sit empty, but could be kept filled if the building air is unreliable. These buildings have a pressure monitor alarm to let us know of a problem. If we have a building air supply that is particularly troublesome, I rig an automatic phone-dialer triggered by the pressure alarm. You are correct to be concerned with audible noise. Rotary compressors whine and reciprocating units rumble. The bigger the unit is, the more noise it makes. The dryers release pressure with a startling blast of air every several minutes. All of our compressors and dryers are installed remote from the spectrometers, either in an attic or pipe chase. The Cryoprobe helium compressor is in a closet. Most researchers are bothered by constant noise, so we also have acoustic panels behind the spectrometer cabinets to help reduce fan noise. If a compressor needs to be sited close to the spectrometer, I recommend building an acoustically insulated closet or box around it. Vibrations should be isolated at the magnet, if possible. With isolation under the magnet, all sources of vibration are isolated. If you only have isolation under the compressor, then you don't eliminate any other sources. If the compressor vibrations exceed the magnet isolation, then of course you need to isolate the compressor also.

Respondent #23 We currently have two NMR rooms with a dedicated compressor servicing the magnets and they are located in a mechanical room next to the NMR labs. In both rooms house air serves as backup, with one being a manual switch over and the other is automatic if the pressure drops below certain level. Each mechanical room has its own heatless desiccant air dryer with corresponding bypasses to allow for maintenance. In one room we have two air dryers, one of which we use as a backup (manual switch). The compressors sit on a concrete bed to minimize vibrations and one of them has additional

1in rubber pads. The humidity of the air is checked constantly by a Dew point monitor (Kahn Cermet II hygrometer) attached to the air line supplying the magnets. The air is generally at -70C or lower (Dew point). One dryer is by Ingersoll-Rand and the other two are by Hankinson. One of the compressors is an oil-based Ingersoll-Rand unit. This has been the biggest headache!!!!. The main problem is the oil slowly saturating the air lines even with filters in line. The second problem is maintenance. IR has state of the art air compressors with computer control. What this means is that your physical plant department has no idea how to fix them when they break or how to do the quarterly oil service. Then you're stock with a $800-$1000 bill unless there is some sort of service contract. This brand is also very sensitive to unregulated current spikes. In the last one we experienced, the computer of the compressor broke and its repair cost about the same as a less fancy air compressor (~$4.5K). Warranty is no good if you don't install an electrical conditioning device before the compressor. The other compressor is a dual scroll pump SOS Powerex system. In the four months of operation I have only had a temperature sensor go bad that didn't affect the performance of the compressor. This unit is oiless and works like a charm. I'm very happy with it. The only minus is that it generates a lot of heat. I had an oil-less Speedair air compressor in the old lab that gave lots of trouble, so stay away from that brand. Even the physical plant people recommended against them.

Respondent #24 In our facility we use compressed air piped in from a UW Physical Plant central supply on campus. The inlet pressure is at about 100 psi and the air is certainly not presumed to be clean. We use an AIRTEK model TW10/TL10, 2-stage (twin tower) heatless desiccant air dryer, which has performed admirably since 2001; it is configured (via dessicant, etc.) to provide -73 degrees C (-100 degrees F) dewpoint outlet air for use with our FTS VT precoolers which operate at -40 degrees C. I had one problem with air icing up early on; I called the company from which we purchased the dryer, and the CEO came out in person the next day and calibrated the cycle and pressure settings. Not a single problem since! (Which reminds me that I should perform a long-overdue annual inspection.) The AIRTEK proved to be significantly less expensive than an equivalent unit from Balston at that time. These types of dryers have no vibrations, only a periodic (e.g., 10-minute cycles) blow-off of air pressure as they switch between towers. Since the dryer is in the NMR lab, I had a nice wooden box built, with insulating material inside, to reduce this blow-off noise; it works pretty well. Air from the dryer is piped through the "standard" Varian-supplied filters and manifold on its way to the spectrometers. In case you're interested, the company information is: Compressed Air Technology, Inc. Dennis Flint, CEO ([email protected]) P.O. Box 697 Marshall, WI 53559 (608) 258-7538 I believe you should do whatever it takes to keep your compressor(s) "sufficiently far" from your NMR

lab to remove the chance for vibration issues. Exactly how far that is depends on several variables.

Respondent #25 Since we've had a some trouble with our compressed air system - here are some elements to consider when deciding what to buy ... We have a Inova with Oxford 500 MHz with 'magnet leg pneumatic suspensions' and a dedicated compressor and dryer for our spectrometer. Our compressor is an Atlas Copco LF 22 ( oil free, gives 9 atm. ), with a 250l. receiver tank ; the dryer is a Silicair Cub (dew point ~ - 60 C.) the back up system is the 'main site' air compressor of our site - In my view, using the main compressor was not really an option for the regular air supply because depending on the number of users , the pressure may drop to very low value causing the magnet to 'land' on the floor ... and the VT to change - So the 'site air supply' line really is only a back up option. Plus we're not sure of the cleanliness and dew point of the site main air supply We decided to buy an NMR dedicated system : Atlas Copco oil free LF22 Unfortunately, we found out that it is not a very good design in that it's just an adaptation of an oil lubricated design (sharing many parts - except piston segments..) In our compressor some bolts were not even made from stainless steel - they started to rust after a couple of months and as a result bits of rust prevented the non return valve to operate normally causing all sort of problems All these ( bolts and a new different non return valve) have been replaced now but we've lost many hours .... The Silicair dryer is OK - we've never had any problems related to condensation ( note that this type of dryer causes a drop of ~ 4 atm on the line hence the need for a relatively high capacity compressor ) We don't have air quality monitoring ( what sort of device would that be ? )

The compressor is in a plant room under the roof on 2nd floor; we're on ground floor never felt any vibration from it - However vibrations from other nearby equipment prevents to run anything but simple one dimensional spectra without the 'leg suspension' acivated

Respondent #26 We experienced problems with our house air many years ago and decided to set up our own air system just for the NMR facility. What we installed was an Ingersoll-Rand, Type-30, 242-5D, two-stage, 175psi, ~19CFM, reciprocating compressor with an 80 gallon tank fitted with an auto-drain. The size of the compressor needed (ie. its CFM value) depends on the type and number of air dryers you are going to put on line. They will generally consume more air than your spectrometers. We run two spectrometers off of each dryer. The basic design of our air system is: 1. The air comes out of the tank and passes through a Parker 2104N-101-DX water/oil coalescent filter. 2. It then passes trough Hankison PR25-230 refrigeration unit. 3. It is then split and passes through two Balston 64-20 (or its equivalent) air dryer. 4. The air is then sent to the various NMR rooms (at 100psi) and then passes through Wilkerson filters, H21-03-F00 and M51-03-F00B in series, and is then regulated down to the desired pressure. The air is dried to a dew point of -50 OC. The Balston air dryer has a color indicator to alert if the air is dry. The system may require a ballast tank on line as some air dryers when purging will slightly vary in air pressure or flow rate causing the spin rate to fluctuate. We have pressure gauges after every device and also have line bypasses for each device so that we do not have shut down the entire system for service a unit. This is important if you want to keep the NMRs running if a dryer goes out. This type compressor is fairly noisy, if you use the Ingersoll-Rand (IR) synthetic oil it is very reliable. It keeps the finger valves from carbonizing. Three years ago we purchased an enclosed IR compressor (UP6RE-10-175, 34CMF) enclosed cabinet (a quiet running compressor), reciprocating type. We had nothing but problems with it. Over the course of those three years we had more service calls on this unit than we had in twenty years on our old Type-30. To IR’s credit they are giving us the full purchase price toward a new rotary screw compressor. We are expecting delivery on it any day. A) The IR Type-30 is our back-up. The way we are set up, if air pressure drops below 145psi the Type-30 will automatically come on. The newer compressor has a 120 gallon tank and both compressor tanks are tied together. B) No! We do not use a back-up, the air coming out of the refrigerator unit is dry enough to safely run an NMR as long as turn off any chillers for “vt”. C) No! The only dryness indicator we use is the one on the Balston Units. We monitor all over. D) The Type-30 compressor is about 25ft from the closes NMR the other one is about 50ft away. They sit on rubber pads. For the Type-30 we styrofoamed the closet to deaden the sound. The other compressornothing. E) I have only had IR compressors.

Respondent #27 I had this done at the XXXX facility: First they agreed to have a N2 line made to most of the spectrometers (for low temperature work only otherwise it is much too expensive). Later my engineer constructed this switch. The current engineer … improved the three-way valve for the 400 solids instrument. If all this will not be possible for you as the Chemistry Department already has a storage tank but is part of a different division of UofC and the biochemists are not interested in getting a tank then you will depend entirely on the air compressor system One point I do want to mention about the dimensions of the system: The air dryer needs a constant flow of air to keep the dessiccant dry. Based on your need for three spectrometers you can calculate from the specs of the air dryer how large a dryer system you need. Then you add the "air consumption" of your dryer to the total flow needed for the spectrometers. That determines the minimum capacity of your air compressor. It does not hurt to overrate it somewhat to give it some rest between times of activity. The systems at XXXX were Kaeser compressors of the screw-type with oil. The oil separation was excellent. Since they do not use pistons, they do not produce a lot of vibrations. You will have to INSIST on good anti-vibration mounts when the installation takes place. Mechanical engineers have no idea of how sensitive NMR spectrometers are for vibrations. The air dryers were Hanki(n)son. Also working well. Here in YYYY we have a dew point meter: it usually reads better than -60 ºC. Yes, we do have a back-up compressor system but I am not sure that it will automatically start up when the main system fails.

Respondent #28 I can tell you a little about my system and offer a few things to think about. Feel free to iterate as much as you would like. (I know exactly how daunting these decisions seem up front!!!) Sorry about the length of this email, but you asked.... We have a science laboratory building here at XXX that is about ten years old. It houses most of the chemistry and biology departments. When the building was built, the designers neglected to provide compressed air to the labs, so the chemistry department had to put in their own compressed air system (before I arrived). We need this compressed air system to provide air to two NMR labs and a N2 generator just upstream of an LC-MS. The NMRs each need under 50 psi, although the air legs that one magnet floats on requires 70 psi. However the N2 generator runs most efficiently at 100 psi, so that determined our base pressure needs. Initially the department installed two scroll compressors working in tandem, but they couldn't keep up with the volume of air required at 100 psi. Also the scrolls were expensive to service. The next system was even worse, in my opinion. The department decided to replace both scroll compressors with a single oil-free compressor (expensive!!!). This teflon lined compressor was under sized and always ran hot. It was expensive to purchase and incredibly expensive to maintain (rebuild/replace every 2000 hours). I don't think that two of these compressors working in tandem would have changed

things much, but at least we wouldn't have been completely down when one compressor was being serviced. Last year, during one of these painful down times, I was finally able to convince the department to replace this system entirely. We purchased a tandem set of two-stage, oil-lubricated piston compressors that were a little oversized for our current needs and set them to run a lower speed. The pumps alternate compressing air to 150 psi, and this duplex system prevents us from losing any air when one compressor needs servicing (belts, seals, etc.). This air gets filtered and sent into a refrigerated dryer, which takes the dewpoint down to -40 degrees. Then this dry air gets sent through a desiccant dryer and filter before giong into a dry receiver. The outlet of this dry receiver goes through a filter/regulator that reduces our pressure to 110 psi on its way to the individual labs. In each lab, we have another set of filters and regulators to dial down the pressure from 110 psi to 50, 70 or 100 psi as needed. (In our NMR labs we actually have small receivers that were left over from our previous system, but they are clearly superfluous.) This compressors and dryers are located in the basement of our building, and the labs are located on the second floor. So we don't have to worry about noise, vibrations, or heat load in the labs from the compressors. Since the air passes through one wet receiver, the dry receiver, two dryers, and several filters, we have enough of a buffer to prevent the vibrations from appearing in our spectra through the air lines themselves. If you need to keep the air compressors near the NMRs, you would probably want to invest in air legs (not cheap or easy to do now with your energized magnets) to decouple vibrations through the floor. The savings up front for this lubricated system made this an easy decision compared to another oil-free system. (I would not ever purchase an oil-free piston compressor, and you can so easily filter out any oil vapors downstream!) The maintenance is easy and inexpensive, too. This system is expected to last 25-30 years before we have to think about rebuilding the compressors. And again, the duplex system provides for it's own backup in the event of a single compressor failure/service. I recommend installing bypass valves and lines around each filter and dryer element for servicing convenience (no downtime!). If there are other, specific questions, please do not hesitate to ask. Good luck!

Respondent #29 We upgraded from a 300 MHz instrument to a 400 MHz that does solids and is better for low temperature work (a Bruker AVANCE 400). Our old piston-type compressor was located in a mechanical room on our roof and was worn out. We got some water and oil mist into air lines in the NMR room. These were trapped in filters before a primary air dryer, an Ingersoll-Rand Model GC, and another dryer, a Balston 64-20, which was added for low temperature work. When the desiccant in the Ingersoll- Rand dryer was changed, there was some oil film on the surfaces. The filters had to be drained weekly of water and a little oil. When we got our new NMR, we wanted to improve the air quality. The system that Cochran Compressor Co. installed here consists of two 10 horsepower base - mount compressors, a panel to alternate the two compressors, two 200 gallon tanks, a refrigerated dryer with a reheater and attendant filters (see drawing). This system was installed in our mechanical room in the basement. The NMR lab is on the third floor. The recommended air requirement for our new NMR is

8.0 cu.ft./min. The oil content of the air must be <0.005 ppm. We have operated at –125C with no problems. The Cochrane equipment feeds into our two pre-existing, in-line dryers with prefilters, one for water and one for oil, in the NMR lab. We have added a ballast tank after the lab room dryers to help alleviate pressure changes due to column switching in the main dryer. There are also particulate filters after the two dryers in the room and one vapor-absorbing filter before the NMR to account for any oil mist that might get to that point. We may be over-filtered now and probable need only the Balston dryer in the lab although I never looked into that. One might configure the whole thing differently if starting from scratch. The downside of piston compressors is that we must be vigilant in inspecting the various filters that are in the compressor room and in the NMR lab. I have seen no evidence of water or oil mist in the filters in front of the air dryers in the lab since we started using the Cochrane equipment (less than one year ago). This may be partially because the compressors are pushing air up and not down as previously but I think our filtration/drying scheme is a good one and would work in other situations. One of the reasons for choosing the piston-type compressors was financially based. I wanted something that would last as long as the NMR. Grant money paid for the compressor system but replacement would come from department operating dollars. That pretty much eliminated the oil-free compressors, which have a relatively short lifetime. Our two-compressor system allows shorter operating time per compressor, increasing their lifetime (we hope). It also means we can work on one compressor and still keep air supplied to the lab. If you have money allocated for periodic maintenance/replacement of compressors, you will have more latitude than we. I assume the vibration concern you mentioned has to do with mechanical vibration from the compressor. Since our compressors are in the basement, we have no experience with that or with noise. If you have any question, please feel free to get in touch with me again. Although I am happy to tell you about our experiences, you should not consider me an authority on the subject of compressors or NMR. Brice Schultz of Cochrane Compressor was very helpful in choosing the size of our compressor and the filtration we needed. That company was also available for installation advice and for a small problem we had after installation concerning the placement of a pressure sensor.

Respondent #30 A) We have a dual compressor system, redundant compressors which alternately run and one can take the load for a few days if the other goes down. Each compressor has its own tank and the tanks have an automatic exhaust to allow any condensate to escape, but our line plugged at the tank and the tank filled with water. B) The dryer runs automatically and no we did not have a backup when ours failed after the water problem above. C) We monitor the pressure at each spectrometer. I have requested the installation of a dew point monitor even if it does cost $1,000 installed. It makes it much easier to demonstrate to repair people that we have a problem. Of course a plugged FTS air chiller is another demonstration. D) The compressors are noisy and you don't want to be anywhere near it. Ours are on lower floors in equipment rooms. They are on mounts. You don't want your office near one.

E) Screw type compressors are the way to go. You want to get what you can get repaired and maintained. These beasts take up space and are noisy. We must have a dryer in New England even if there were no FTS air chiller to worry about. Best of luck. I am currently trying to sort out our machine usage in the last few weeks when people had to work around compressor maintenance time and compressor and air dryer failures. I believe our maintenance people are purchasing a spare compressor. FOLLOWUP, Respondent 30 NONONONONO to piston compressors. We have them on our 800 and the systems are not designed, we were told after the fact by the service engineer, to run 24/7. We have a pair which run alternately. There is a valve after each compressor which opens for each cycle of the piston. I can send you a picture of a busted valve. It lasted only a few months. And if screw compressors are noisy these are worse in my opinion. The cheap device we use to demonstrate dryness is a filter full of water absorbing beads which change color in the event of a failure. This is located where I can see it without going into the mechanical room. It is not perfect but it beats nothing. Now I am going for an indicator where the service engineers can see it. We do have a wonderful building services supervisor in the sciences and we do have our own systems. But when we do have problems they always take longer than anyone might have imagined to resolve.

the posted query: respondents #1,2

Documents