A milk cartonful of outer space: my ultra high vacuum setup! - Page 1
Forum section: electronics / projects

author: ChristofferB
author_rank: Frequent Contributor
timestamp: November 19, 2020, 11:33:02 pm
content: Thought I'd share my vacuum progress with you!I've finally collected enough parts to spin up my turbo pump! It's running at around 60.000 RPM and is creating a vacuum in the order of 10^-6 to 10^-9 mbar!So far I only have a quartz viewport to cover the pump on the ultra high vacuum side, I will soon get an actual chamber, so I can mount a penning gauge and actually determine the pressure.All the gauges, and the turbo controller are Edwards vacuum products, and the documentation is great, building controllers for them is a breeze.Here is seen the turbo controller:And the entire setup! There is a 2-stage rotary vane pump under the table providing about 0.1 mbar of foreline vacuum; the turbo would disintegrate if run at atmospheric pressures.Hopefully I will find something to actuallydowith the vacuum at some pointThe turbo is an Edwards EXT255H, with an EXDC160 controller (with homemade PSU and interface), and an APG-L-NW16 pirani gauge on the rough vacuum side.My high vacuum sensor is an AIM-X-NW25 "active inverted magnetron gauge", which will measure down to 10^-10 mbar I believe. Not yet installed.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: November 20, 2020, 12:14:22 am
content: I'm fascinated by vacuum. Sounds fun!

author: profdc9
author_rank: Frequent Contributor
timestamp: November 20, 2020, 12:53:50 am
content: How about a scanning electron microscope?

author: mag_therm
author_rank: Frequent Contributor
timestamp: November 20, 2020, 05:19:06 pm
content: Excellent job.You will be able to offer a vac impregnation service for all theferrite cored components.

author: Wolfram
author_rank: Frequent Contributor
timestamp: November 20, 2020, 10:00:02 pm
content: Awesome, nice to see that this obscure hobby has some more representation in the Scandinavias!I'll use this occasion to shamelessly share some pictures of my own exploits within the field. Through years of hoarding, I have more turbo pumps than fingers at the moment, but I mostly use diffusion pumps when evacuating glass vessels.

author: ChristofferB
author_rank: Frequent Contributor
timestamp: November 21, 2020, 01:05:08 am
content: Cool looking setups! I love those little KF40/KF50 diffusion pumps!Diffusion makes sense if you're doing vacuum tubes and other stuff that may implode, absolutely.

author: robzy
author_rank: Regular Contributor
timestamp: November 21, 2020, 01:37:56 am
content: Y'all have some cool toys!

author: ChristofferB
author_rank: Frequent Contributor
timestamp: November 23, 2020, 08:08:07 pm
content: Chamber arrived, looks like it got bent in the mailSo I can now report a vacuum slightly better than 10^-6 torr (~ mbar) after 15 min's of pumping time!I'm so pleased with this! Please enjoy!

author: richnormand
author_rank: Unknown
timestamp: November 23, 2020, 11:51:53 pm
content: Quote from: Wolfram on November 20, 2020, 10:00:02 pmHigh vacuum technology has a nice intersection with electronics indeed. Particularly when I did my initial turbo pump drivers and many of the repairs on the gauge controllers and particularly dealing with the RGA unit (R65Cxx microprocessor and support chips family and failed old aged UVPROMs all needed loving care and refresh as some were damaged by the RF HV it looks like. Took me about 6 months to get the electronics in order).Also included my shameless plug photo.@ChristofferB Thanks for posting.For those interested, another good place for vacuum stuff is fusor.net.

author: ChristofferB
author_rank: Frequent Contributor
timestamp: November 24, 2020, 12:47:20 am
content: What a nice setup! Is that the magnet of an ion pump I spot?An RGA is definitely on my wishlist as well! Finding one that doesn't require non-included proprietary software turns out to be tricky though.

author: coppercone2
author_rank: Super Contributor
timestamp: November 24, 2020, 12:51:39 am
content: do those flanges and things fall under some kind of common international dimension specification for high purity vacuum work? or is it all custom? (like waveguide is standard)

author: ChristofferB
author_rank: Frequent Contributor
timestamp: November 24, 2020, 01:10:31 am
content: They're standard. The ones on mine, the big pump flanges are called ISO-DN100, (for 100 mm), the small side flanges are KF-25 (mm) and the bolt circle ones seen in the last pic are "conflat". Those are the 3 main families, and they all come in a handful common sizes.

author: richnormand
author_rank: Unknown
timestamp: November 24, 2020, 02:21:23 am
content: Quote from: ChristofferB on November 24, 2020, 12:47:20 amIt is an ion pump. At the end of using the system I let the turbo bring the chamber down , valve it off, turn the turbo off (the two high pressures on the readout, top one is the chamber at 10^-9 torr) and engage the ion pump.At low pressure it only takes a few uA from the Ortec PSU and I leave it on all the time. Keeps the system clean and prevents contamination of the RGA column seen on top of the chamber.As far as finding an RGA at a reasonable price it is a matter of patience. Many are just parts like the quadrupole, or the RF box or the controller. More modern instruments are integrated, but still an issue to end up with a full system at a reasonable cost. A few like SRS will allow you to download the program to run it. Some others will charge a lot of money or like mine the company has been absorbed in a merger years ago. I was fortunate as the seller asked me if if I wanted to pay extra for the computer system. That is the way I got the software. First thing I did was to clone the HD! The real issues were the hardware and electronics. It took a while to troubleshoot and debug without schematics. Also I was lucky to find the user manual on a US university site via Google.Speaking of turbo pumps keep in mind these things pack a lot of kinetic energy at full speed. Make sure it is fastened securely on dampers, so it will not be bumped, no parts from your system can be inhaled and if it crash it does not rip everything an fly in your face. A story I heard was a company making a small turbo that a salesman had running on the demo table, moving it in the palm of his hand, due to the motion it crashed and broke his wrist...

author: coppercone2
author_rank: Super Contributor
timestamp: November 24, 2020, 07:15:36 am
content: what can you do with this setup? I built something nice (high quality degas chamber with stainless plumbing etc), but it has little uses out side of glue.. plus the mix nozzle largely took it out of the equation for meI only ever saw systems like this hooked up to like particle accelerators, is there anything you can do on a small scale? I think its too much for making tubes.. the pumps are too expensive and draw more then you need, plus I think the contamination would kill them from typical tube making processesAlso, does it have some kind of shut down if it detects air ingress to prevent dangerous operation? i kind of lose interest if it requires a multi million dollar accelerator to go along with it

author: Jan Audio
author_rank: Frequent Contributor
timestamp: November 24, 2020, 05:02:17 pm
content: May i ask what you do with it ?, can you make a movie.thnx

author: ChristofferB
author_rank: Frequent Contributor
timestamp: November 24, 2020, 10:08:21 pm
content: Quote from: richnormand on November 24, 2020, 02:21:23 amThat's about what I figured, with the RGA's. It might actually be cheaper to just set up a full-fledged MS from a GC-MS system!Good note about the salesman! So far my turbo is only attached via the backing vacuum hoseAs for what to do with a setup like this, here is a list of future projects I intend to try at some point:--physical vapor deposition--sputtering--making ion guns and tiny linear accelerators (perhaps for low-energy electron diffraction, or EDX spectroscopy (it's like x-ray fluorescence spectroscopy but using electrons)--DIY quadrupole mass spectrometer--various plasma experimentsI've actually gotten almost all the equipment on there I wanted, at the moment. I only need to find/make some electrical feedthroughs. Ideally both a HV one and a multi-pin low voltage one.I'm considering just drilling a hole in a aluminium KF25 end cap and then affixing some teflon coated wires with some distance in the hole, and filling the hole with that Hysol-1C ceramic vacuum epoxy. either that or find a used hermetic chassis connector (like a LEMO or something.)Does anybody know if there's any issue using the chamber housing as return path for HV electrodes in the chamber?

author: james_s
author_rank: Super Contributor
timestamp: November 24, 2020, 10:50:41 pm
content: I picked up a turbopump some time back but I still need to get around to building a driver for it. Years ago I refurbished a mechanical pump and was able to get the pressure down to under 3 microns IIRC after a few days, high vacuum is neat "stuff" and it's shockingly hard to plug up all the leaks in a system.I always thought it would be cool to make vacuum tubes and CRTs.

author: richnormand
author_rank: Unknown
timestamp: November 24, 2020, 11:15:47 pm
content: ""Does anybody know if there's any issue using the chamber housing as return path for HV electrodes in the chamber?""Depends on the type of work you do but I personally think it should be well grounded in all cases.The type of work done by the folks on fusor.net for example, as you know, would be dangerous if the chamber was floating by accident.If you are reading nanoamps with vacuum feedthroughs a proper shielding with guard rings is needed around the wires (triax). In both these extremes I would suggest the chamber to be well bonded to a solid ground.However I do not use the chamber as a return path for individual equipment. Each should have its own (beware of ground loops). Consider the situation with an ion gauge or other device with medium to high voltage, pressure goes up and a discharge ensue and goes all the way to the roughing pump electrifying everything on its path (in particular if using a rubber hose on the roughing pump).Safety first! Do a search on this as there are several warnings from manufacturers on the subject.As far as I am concerned (my opinion, YMMV) I like to know that everything I touch on there is properly grounded, like my bench instruments.

author: richnormand
author_rank: Unknown
timestamp: November 24, 2020, 11:29:25 pm
content: ""I picked up a turbopump some time back but I still need to get around to building a driver for it""I made my own driver for my turbo (TPH055) from several docs on the web. It worked OK but was inefficient (used halogen bulbs to soak up the transients on startup).For example, in case of a sudden loss of the power supply, the turbo was acting as a generator and would fry the output devices! I had to always keep the logic power on while the turbo would spin down so the Hall effect sensors on the turbo would still trigger the circuit properly.Eventually I got a proper one.Also it will depend on the exact topology of your unit like number of phases, triggers for position, max speed, temp cutoff sensors etc...Be safe these things can pack a wallop of energy if they suddenly crach.

author: Teledog
author_rank: Regular Contributor
timestamp: November 25, 2020, 12:09:59 am
content: Collected a bunch of UHV parts here myself, was going to do metal vapour deposition (via tungsten crucibles).A monster Varian diff pump, but only have hydrocarbon oil..I'll wait until I can get Santovac(x), scared of blowing the vacuum ..burn/mess with HC oil.Need more $, real-estate & time..sigh..PS: for leak detection..use a lecture bottle (Costco balloon tank?) "drizzling" helium in a small hose around the suspected leaky areas while keeping a close eye the vacuum..bingo!Good luck!

author: james_s
author_rank: Super Contributor
timestamp: November 25, 2020, 05:03:17 am
content: Quote from: richnormand on November 24, 2020, 11:29:25 pmMine is a little Leybold pump that uses a 3 phase induction motor so I don't have to worry about it turning into a generator if power is lost. I'm aware of the kinetic energy they hold, it's important to securely attach them to the chamber.

author: Circlotron
author_rank: Super Contributor
timestamp: November 25, 2020, 06:30:36 am
content: Quote from: ChristofferB on November 19, 2020, 11:33:02 pmPut a book in the chamber and suck all the acid out of the paper, then pump in some kind of preservative vapour so your book will last forever, not turn to powder in maybe 100 years. That's whats going to happen to all our books that have acid in the paper. The pages turning yellow is just the beginning.

author: AlfBaz
author_rank: Super Contributor
timestamp: November 25, 2020, 06:40:45 am
content: Quote from: ChristofferB on November 19, 2020, 11:33:02 pmNo need. We have volt and time nut groups just start a vacuumnut mailing list

author: coppercone2
author_rank: Super Contributor
timestamp: November 25, 2020, 07:38:33 am
content: It's kind of a let down when you build a machine that does nothing, at some point its like having a weird shaped bracket for no reason.cashmir effect?

author: LaserSteve
author_rank: Super Contributor
timestamp: November 25, 2020, 03:49:54 pm
content: I have dual stage roughing pump, 250 L/s Ion pump, Leybold TMP150 turbo, and the all important tube pinch-off tool for cold welding fill stems on home-made tubes.I use it for repumping sealed gas lasers. Have Krypton, Neon, Argon, on station, with Helium coming soon. I've been known to seal the 1$ a piece strobe tubes into copper sleeves to obtain a little Xenon. Have a big transformer for vacuum deposition.I'm afraid you have not yet began the fight, collecting all the accessories takes time and patience.Did I mention the outrageous cost of small quantities of sealing glasses compatible with Kovar? (Dumet and type 80 Lead Glass is child's play) Glassblowing torches were not inexpensive either. Darn beadmakers buy all the nice used ones.. This can make the T.E.A. thread look like lunch money. "What do you mean you only want a few meters of Ytterbium Oxide doped Molybdenum foil for sealing in quartz?, My dear sir, most of our clients order kilometers at a time for halogen lamps" I need the welder, Tig welder, micro size, and then I will be really, really set up for making hollow state. You know, the pulsed TIG that only goes down to a few amps, orbital welding stage optional...Just getting the pump is a start, call me when you have a few bellows valves. Most difficult thing to do, besides pinch-off, is making controlled leaks for gas filling. I ended up using a tiny space between two refrigeration grade solenoid valves. Open valve A, fill tiny chamber, Close A, open valve B to allow gas to flow into process chamber or plasma tube. I jokingly call it the Sigma Delta fill process.One trick is to run the coils on AC instead of DC, that way the pintle bounces off the internal rubber seal, and you can "buzz" gas in slowly.RGA, no.... quickly found out how to live without that. A tiny 2 L/S Ion pump and a little alcohol is your friend in leak detection, and quite cheap, too. Some of the older Varian table top helium leak detectors are quite repairable.In my case, the Turbo and the Ion Pump came from an engineer who bought a plant for producing tubes. He needed the expertise in vacuum and plasma, I needed, well... Vacuum. So for some of his leftovers I did quite a bit of teaching. Pinch-off tool was 1100$ in the early part of the century, now they retail for 3600$ for a manual one, double that for hydraulic.Flying full size airplanes would be cheaper...Swagelok fittings and OFHC copper tubing or steel tubing is your friend, trade off time for the lower conductance if need be. I typically get 1x10-7 to 1x10-8 out of the cheaper Swagelok, much more out of the ones with the crushable seals.For God's sake, if you ever have the chance to take home even a modest sized bell jar, grab it... Those chambers are NOT cheap.Heat tapes, have to have miles of heat tapes on a good Variac. That and a small propane torch for aiding outgassing. It never stops amazing me how much trapped gas and water vapor ordinary stainless steel can hold on to.One of the most important things you can do to further your projects is buy a mini-lathe or a good full size lathe and some tooling.Steve

author: coppercone2
author_rank: Super Contributor
timestamp: November 25, 2020, 06:51:22 pm
content: do you need a turbo pump for lasers and vacuum tubes? I thought it drew too low.Does it have to do with not wanting a getter in lasers because it could contaminate the filament, so you put the getter far away and seal it off with a pinch? For traditional tubes I thought the getter took care of the ultra low pressure requirement and reduced pump complexity.

author: LaserSteve
author_rank: Super Contributor
timestamp: November 26, 2020, 12:01:13 am
content: Getters are the subject of whole books. For a glass receivingTube or tungsten light bulb on a sealex machine in production, relying on the getter for final vacuum is economical.Not all getters sorb rare gas, others can only pump during deposition., some use reactive materials, others can sorb after deposition. The chemistry is wide, and depends on what you want to doTungstenLight bulbs often just get a tiny shot of Phosphorus Pentoxide on the fill stem for example. Rare gas and nitrogen are not a threat to the filament, but oxygen and hydrogen are.What I like to work on, metal ceramic ion laser tubes, had their getters designed out in their third generation. Gettering being replaced by an incredibly hot oven bake out during processing..Other laser tubes have getters for scavenging hydrogen and water vapor that is retained in the welds, which outgas over time.With the exception of flowing gas lasers that are pumped in real time, I can't think of any tube processing condition where there is a situation of "too high" an initial vacuum.

author: coppercone2
author_rank: Super Contributor
timestamp: November 26, 2020, 01:42:25 am
content: the pumps are more difficult to maintain and more expenisve to run thoughthe oven might be easier to achieve then a vacuum (SiC elements)

author: ChristofferB
author_rank: Frequent Contributor
timestamp: November 26, 2020, 07:17:42 am
content: There is usually not that much maintenance in an UHV system once it is set up. If you dont pump nasty vapors and everything is fairly clean, we are talking a roughing pump change maybe each 6 months, that's it.All of this vacuum gear is designed for continuous use, pumps can run continuously for months at a time. It's quite impressive actually

author: Non-Abelian
author_rank: Contributor
timestamp: November 26, 2020, 01:00:21 pm
content: Quote from: ChristofferB on November 24, 2020, 10:08:21 pm

author: james_s
author_rank: Super Contributor
timestamp: November 27, 2020, 05:38:50 am
content: Quote from: ChristofferB on November 26, 2020, 07:17:42 amIf not for the power consumption it's usually better to run them continuously, the roughing pump at least. When it has been at atmospheric pressure for a while the oil and other objects absorb moisture and other things from the air and can outgas for days when you pump it down.

author: ChristofferB
author_rank: Frequent Contributor
timestamp: November 27, 2020, 11:43:05 am
content: Right. And if that's impossible, I think a decent compromise is venting the vacuum chamber to dry nitrogen or argon, so the moisture and pollutants in the air won't get sucked back in.I have a turbo vent solenoid, and I'm considering adding one of those small single use welding argon cylinders to my setup as vent gas.

author: richnormand
author_rank: Unknown
timestamp: November 27, 2020, 05:15:42 pm
content: Quote from: james_s on November 27, 2020, 05:38:50 amSince mine is the foreline pump for the turbo I usually valve off the turbo from the rotary pump, shut down the rotary pump and vent it. Doing that for ages (25 years plus) without any ill effects.Two points to take into account are that it is the forline pump for the turbo (same argument for a diff ) so it matter little if it start at 15-20 mtorr and slowly goes to 5 as it warms up.The other is that if the ultimate is bad because the oil has some humidity in it I just leave it running with full ballast on the last stage. The pump will warm up and drive the humidity away in about one hour and get back to baseline.I would guess that the only reason to leave the rotary pump all the time is when used on a system that needs a diff pump 24/7, like some SEMs that do not have ion pumps.In addition I do not need the constant noise and electricity bills associated with it.Final though: since my main chamber is maintained by an ion pump I do not need to keep the whole mechanical side running all the time, even when running chip and device leakage measurement with the RGA.

author: ChristofferB
author_rank: Frequent Contributor
timestamp: November 27, 2020, 06:10:41 pm
content: Well, for a less than happy conclusion, my turbo is cooked..The turbo now makes a constant pitch whining noise so loud it's impossible to be in the room.The shutdown procedure in the manual isn't really applicable for a small-ish chamber. I think the rotor has become unbalanced.There is no way of operating the vent valve on the pump body careful enough to not shock the pump if the chamber is very small. A larger chamber would react more sluggishly.I guess vacuum experiments are suspended until I find a new Edwards turbo.. bummer.

author: coppercone2
author_rank: Super Contributor
timestamp: November 27, 2020, 07:18:05 pm
content: see if you can do something with a kiln, they are actually serviceable, but the elements are expensive. I never liked pumps save for magnetic drive water pumps.this getter pump, that is heating a pipe coated with a highly oxidative metal? It sounds like the job for a tube furnace.

author: richnormand
author_rank: Unknown
timestamp: November 28, 2020, 12:09:14 am
content: Don't despair immediately. It could be a bearing. Not cheap but still affordable.Turbo bearing are quite finicky when the pump has been in storage for a time and recently put back in service without being re-oiled.Try to gently turn the top blade with your cleaned finger (dishwater soap clean to remove skin oil and a bare finger will give you a good feedback not to apply too much pressure) and see how it spins and how long.Unless you vented it at speed (bent a blade or something) they don't become unbalanced that easily.Although not recommended procedure ( to avoid resonnances and other ??) I always let turbo pumps spin down a lot (many years in lab) before shutdown procedures.Mine at home (TPH055 if I recall correctly) is magnetic on top and ceramic bearing on the bottom.I let mine spin down by itself with the forline pump working until very low rpm before shutting down the foreline valve at around 10^-4 torr.Mine takes about 20 minutes to do so and if the time becomes noticeably shorter it should be a good indication of some drag issue I think.

author: ChristofferB
author_rank: Frequent Contributor
timestamp: November 28, 2020, 12:46:43 am
content: One could hope so. I'm going to consult my uni's mass spectrometry guy next week.Unfortunately, Ididhear a "brrbrrbrrbrr" sound as I cracked open the vent valve, so I was already fearing this to be the case.Turning the blades by hand is pretty smooth, and it stays spinning for quite a while. That said, there is a tiny scraping sound.I think the EXT255H uses a very standard lower bearing, so it might be replaceable with decent standard industry part. I fear getting it fixed proffessionally will be more expensive than just getting a second EXT255 off of ebay.Lesson learnt, though. In the future I'll just let the pump run down to a stop with the roughing pump running, then vent.Edit: I just re-read the manual, and based on the info about venting, I'm reading it as one CAN'T damage the pump be venting at below 50% speed."However, if you vent the pump when it is at full rotational speed and the rate of pressure rise is too high, the pumplife may be reduced. We therefore recommend that you either limit the vent rate (see Section 2.3), or only open thevent-valve after the EXT pump speed has fallen to 50% of full rotational speed.The rate of pressure rise cannot be controlled by the manual vent-valve, so if you use the manual vent-valve, youmust only open the vent-valve after the EXT pump speed has fallen to 50% of full rotational speed."also, even if the pump was only at 20% speed, that's still 12000 rpm - and there are something like 20 blades per stage - if it was catching on something it would NOT sound like the slow ~ 10 hz bump sound I heard.Maybe it is the bearings.

author: james_s
author_rank: Super Contributor
timestamp: November 28, 2020, 02:39:53 am
content: I remember reading somewhere that the lubrication in these things has an expiration date and they can fail just sitting in storage. They are also incredibly expensive to overhaul, I don't think it's the sort of thing a hobbyist can typically do themselves. If it's making a scraping sound when turned by hand then I think it's pretty safe to say that this one is done.So it has a purge valve on the pump itself? Seems like what you want is a valve with a virtually microscopic opening so you can create just enough of a leak to allow air to fill the chamber over a period of several minutes. I don't think it's a good idea to start letting air in until the turbo has spun down to a crawl.

author: ChristofferB
author_rank: Frequent Contributor
timestamp: November 28, 2020, 01:51:41 pm
content: Quote from: james_s on November 28, 2020, 02:39:53 amYeah it's strange. there is a list of orifice-sizes for various chamber volumes, for when a solenoid is used, and for those orifice sizes, it's apparantly safe to vent at 100% speed!-but as mentioned above, for the manual valve, it just sais to be safe by doing it under 50%This is a combined turbomolecular/molecular drag pump, so I think the idea is that the vent valve enters in the drag stages which can handle much more gas ballast than the first few blade stages.THERE HAS BEEN A DEVELOPMENTas a last-ditch attempt at pinning the tail on another part of the donkey, I tried unbolting the pump from the table and adding some layers of gel tape underneath it and just finger-tightening the pump back onto the table.This reduced the whining from so loud it drowned out my 2-stage rotary vane pump to so low you can stand being in the room.The dominant frequency is about 1 KHz. Perhaps I'm just hitting a resonance modejustright. The sound definitely is still there, so the bearing might not be brilliant, but this might actually be useable.The pump doesn't get hot. it's coasting at around 30 degrees with no active cooling.

author: james_s
author_rank: Super Contributor
timestamp: November 28, 2020, 09:47:53 pm
content: Given the violent catastrophic way in which these things can fail, that would make me really nervous. If it's making a scraping noise when rotated by hand that's a really bad sign, I personally would not run it until I figured out what was making the noise.

author: coppercone2
author_rank: Super Contributor
timestamp: November 29, 2020, 12:58:02 am
content: are they not built to withstand the internal destruction of the rotor?in that case the first thing you should do as a hobbyist is armor it, because thats not worth it.

author: LaserSteve
author_rank: Super Contributor
timestamp: November 29, 2020, 03:20:19 am
content: Guy at work once told me where to buy the bearings cheap if you live in North America.If he is not already taking the nearly month long Xmas vacationthat his level of greybeard seniority rates, I'll get the name of the company.He says not difficult to rebuild, and he's only been doing vacuum for 30 years.Active cooling was optional on mine and I find it runs better with the cooling water on.Steve

author: richnormand
author_rank: Unknown
timestamp: November 30, 2020, 07:31:19 pm
content: This is where I get my bearings:https://alpinebearing.com/bearing-categories/turbo-pump/Prices are resonnable compared to originals from the manufacturer.I get some vacuum stuff:https://www.duniway.com/They have excellent stock but the paperwork to export from the US is a PITA.The web site is full of good information.

author: james_s
author_rank: Super Contributor
timestamp: November 30, 2020, 08:13:28 pm
content: That's cool, I was under the impression that rebuilding a turbopump was the kind of thing that required expensive specialized tools and not something a hobbyist could reasonably do themselves. Roughly how much does a set of bearings for a small turbopump cost?

author: ConKbot
author_rank: Super Contributor
timestamp: November 30, 2020, 09:29:20 pm
content: Quote from: coppercone2 on November 29, 2020, 12:58:02 amBlades coming out arent the problem, the problem is all the kinetic energy coming out at once. Edwards STP series with ISO100 flange(130mm flange OD, approximate CD size) saying to design for 3.8kNm of torque (2800 foot pounds), 12 kilo pump, capable of exerting that much torque is going to destroy all sorts of things if it can get up any sort of velocity.https://www.idealvac.com/files/manuals/edwards-stp-301-451.pdfNevermind its big brotherhttps://www.lesker.com/newweb/vacuum_pumps/pdf/manuals/edwards-stp-xa2703-xa3203.pdfIso 300 flange, 425mm OD, saying to prepare for a 71.2kNm (50k+ foot pounds!) kick when you manage to break it.

author: james_s
author_rank: Super Contributor
timestamp: November 30, 2020, 09:37:17 pm
content: Yeah good luck stopping that from tearing loose and wreaking havoc, or trying to fully contain it. The best you can probably do is preventative maintenance and monitoring to avoid catastrophic failure in the first place, and arranging things such that if it does happen hopefully it will go off in the direction of least collateral damage. It's not like they seize up on a daily basis, it can happen but it's rare.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 30, 2020, 10:01:02 pm
content: A torque comparable to that delivered by the rifling of a gun barrel... and this is no accident, I would say.Would imagine a helical accordion tube of suitable length and thickness is what you'd need to absorb that kind of transient... or else a lot of mass on the mounting flange, and a little flex between the mass and the rest of your system.Tim

author: coppercone2
author_rank: Super Contributor
timestamp: December 01, 2020, 12:01:29 am
content: well a weld or silver braze can hold between 50000-80000 (average high silver braze/super high quality braze with good spacing) -150,000 (top end weld) PSI, so it looks like to be safe you would want 3-4? square inches of weld or 8 square inches of braze (double capacity).That means the actual weld area, not the area under a welded flange. So if the body had a 3x3 inch flange or pedestal, it would need to be fully brazed to a big steel plate to handle it. Welding is more difficult you would need to figure out how to join it. With good epoxy glue you would need a perfectly jointed 5x5 inch flange (25 square inches bond area).Correct me if I am wrong. I imagine not getting it to distort and stuff is hard, the best I could think of is to pot it inside of a big thick steel cube with a heavy flange on it. Getting into millwright stuff I think. Obviously it would not be easily serviceable anymore.I imagine it may have thermal problems if you do that also.Can someone do the units here I think its wrong?

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: December 01, 2020, 01:51:11 am
content: ChristofferB,You might also want to check out the fusor forum, the vacuum technology section.https://fusor.net/board/viewforum.php?f=10There are tons of good stuff there including some turbo repair posts.Cheers,Corby Dawson

author: ChristofferB
author_rank: Frequent Contributor
timestamp: December 10, 2020, 09:53:19 pm
content: I think I was hasty/paranoid fearing a bad pump. I think it's fine.-it never gets hotter than ~35 degrees C-I measured the current, it draws 2A (=160W) on speed ramp-up, but once it reaches that it very rapidly tapers off to 460 mA (=37W) once at 100% speed.-It has a high pitched turbine sound, but it's drastically lowered, now that I've mechanically decoupled the pump from the table. now it's just a low 1khz hum.That doesn't sound like a pump that's struggling to me.What are your thoughts?

author: coppercone2
author_rank: Super Contributor
timestamp: December 10, 2020, 09:58:55 pm
content: invest in a DSA and rubber dampers of the correct durometer to stabilize and monitor the system, it is potentially dangerous based on what people say (the thing you bolt on both sides with rubber in between).You should probobly keep DSA readouts with the correct sensor based on pump life time to monitor its degradationIt seems like a serious questionAlso find out if its appropriate to put rubber standoffs on it, I am not really sure. There is also the other vibration stabilization system consisting of something being elevated on things made of cable.https://www.avproductsinc.com/wire-rope/mounts.htmlThe rubber might make the failure mode worse, the cable might be able to handle it?you can also get combos with cable wedged between a silicone or rubber pad depending on frequency I think.Or at least put it on a thick steel plate then put that over the table with vibration isolatorsbut keep in mind I think if you put isolators it can resonate if you do it wrong

author: ChristofferB
author_rank: Frequent Contributor
timestamp: December 10, 2020, 10:09:57 pm
content: That would be belts and braces, for sure. I've just never seen it actually done in labs or industry.My exact pump comes from a small (AT PC case sized) benchtop mass spectrometer, which just stands losely on a benchtop.and a high speed motor that draws very little power, doesn't get hot and doesn't make wierd noises just doesn't seem like it's in that bad shape.Maybe I'm rationalizing because I don't want to re-bearing it but that power measurement made me much more at ease.it's down to using 23W now.

author: richnormand
author_rank: Unknown
timestamp: December 10, 2020, 11:28:19 pm
content: "Maybe I'm rationalizing because I don't want to re-bearing it but that power measurement made me much more at ease."From what you described the start up current and low whine at speed looks/sound normal. On my homemade driver I was using car halogen lights to limit current on startup. They would glow brightly until coasting speeds were reached.I assume you have a commercial driver that will limit current and monitor rpm coasting time.Even if quiet at speed keep an ear open while it is ramping up from start for resonnances. If they grow with time that is an indication of potential issues in the future.On safety note that in most applications the pump resides under a table or in an enclosure, not in the open just held by the vacuum hoses. Of the three large turbo I have seen (after failure, as they destroyed themselves during the night) only one had a history of increasing noise.That one just damaged the electronics and was very hard to turn after (seized bearing and blown output FET) Motor and rotor were OK (factory rebuild). The other two were a total mashup of scattered metal inside. All three were bolted on a large stainless steel vacuum assembly and had nowhere to go. They were all enclosed under the chamber anyway.

author: coppercone2
author_rank: Super Contributor
timestamp: December 11, 2020, 04:33:17 am
content: What exactly happens when one of these things goes loose? Can it bludgeon you like a medieval mace? That is what comes to mind when I think about the damage, it would be a metal object on a hose (by mace I mean the one that is like a cannon ball on a chain). Does it have enough strength? Or is it more likely to 'shoot you' with something from the inside?https://en.wikipedia.org/wiki/Flail_(weapon)I assume it was enough to ride by someone on a horse and hit them in the head (archers with leather hats)

author: ChristofferB
author_rank: Frequent Contributor
timestamp: December 11, 2020, 12:22:14 pm
content: I have considered the flail/mace scenario. The pump is anchored to a very heavy rotary vane pump on the floor via a metal spiral rigidized plastic hose, so it probably won't come completely lose. I've bolted mine to the table plate with a sandwich of 10x10 steel plate on each side to distribute forces over more wood tabletop, bolts are M5.There is a screen over the rotors, but it's very flimsy, and only sits by friction, and the next thing projectiles from the disintegrating pump meets is a large glass (quartz?) window. cracking this will implode it, but since it's only a single window, shards will be pulled inwards, remember even if the turbo dies, there is still a vacuum of 0.1 to 0.01 mbar in the vessel.Even then, I have actually considered adding a lose-ish thick perspex outer window, just to stop high speed shrapnel in case of implosion. But I really don't think it's necessary.I want to be able to seal and leave the chamber overnight with rough (0.01 mbar) vacuum, so I don't have to drive off atmospheric moisture every time I'm using it, so it will be static, pumps off like that.

author: coppercone2
author_rank: Super Contributor
timestamp: December 11, 2020, 09:28:40 pm
content: a piece of lexan would do something and its useful to have it in the shop (home depot sells 0.1 inch thick ones for garage windows) for ~15? dollars or soI assume what could happen is glass can fall into whats left of the rotator and then be launched out like a being hit with a golf club.

author: ChristofferB
author_rank: Frequent Contributor
timestamp: December 11, 2020, 10:52:56 pm
content: well there's still a fine mesh over the turbine blades, but better not take chances.Also, turning around and hitting the pump window from the outside would also be bad, so it's just a nice extra thing to have.I think I've decided I trust the pump is OK for now. I'll monitor the sound and power, of course.Next stop is making an electrical feedthrough. I think my best (read:cheapest) option is to get some brass KF25 flanges, drill some holes and soft or silver solder in some solderable hermetic feedthroughs.These are particular cheap and soviet-like :https://www.ebay.com/itm//261672048845but if they survive soldering, I'm not so worried about their durability. I can vacuum test them with just my mechanical pump first.

author: ChristofferB
author_rank: Frequent Contributor
timestamp: December 13, 2020, 01:33:01 pm
content: For anyone interested, I made a little video going through my vacuum system! Hope you enjoy.