My new setup

How to get to vacuum, what the classes are, and what is needed for what job.

Re: My new setup

Postby Jerry » Tue May 27, 2014 12:38 am

Got the pump installed, plumbed in, and running yesterday. It has been running about 30 hours now and is at about 8e-7 torr right now. I thought I had a leak but I cant find a thing with the RGA in leak check mode and a bottle of helium. I think it must be all the water in the system from everything being up to air for so long, especially since I had to rinse the valve body out with hose to get all the crud I scrubbed off out of the system. Well see where it is before I leave for work tomorrow.

I still need to tie the pump into the frame and hook up a couple more pneumatic lines for the roughing valve on the chamber. I used a dual stage valve that allows you to softly pull down the chamber without disturbing things in the chamber.

ImageTurbo pump installed and running by macona, on Flickr
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Re: My new setup

Postby Jerry » Tue May 27, 2014 3:49 pm

I shut everything down before I headed to work and the chamber was down to 5.5x10^-7 torr. Not bad. Better yet after a half hour the pressure in the chamber was still 8x10^-5.
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Re: My new setup

Postby johnf » Wed May 28, 2014 5:21 am

Jerry
No big leaks there
a Week or two of pumping continuously will outgas all and let you see base pressure.
We get this at work all the time.
for opening backfill with dry gas before opening and pump down again before shutting down.

you got to keep that water out it's a@#%#$^%
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Re: My new setup

Postby Jerry » Thu May 29, 2014 1:28 am

I fired it up after work today, the first time since I shut it down monday. Within two minutes of turning the system on it was already down to the -5 range and the turbo was only at 25% speed! As I type it is somewhere around the 6e-7.

I need to get another bottle of argon or N2 for backfilling.

One thing I am thinking of doing is putting the three phase motors back on the rotary pump and blower and tie them into the foreline pressure to slow them down when there is little gas load. It would save a bit of power, noise, and vibration. I cant really stop the blower as it is, it kills the conductance when stopped and the foreline pressure builds up pretty fast. I already have a couple VFDs I could use.

I am also adding a UPS to the turbo pump. In a power outage the drive regens until about 30% speed where it drops the rotor onto it's landing bearings. You get 5 landings like this before they have to be replaced. I have no idea if it has ever been though one of these hard landings before and dont want to find out. In the even of a power failure the UPS will trigger the valves to close and the turbo to stop which takes about 10 minutes. It is a pretty hefty UPS, APC 3000VA 240v, 19" rack mount with relay option.
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Re: My new setup

Postby Doug Coulter » Mon Jun 16, 2014 8:46 am

Jerry - if you can find a valve, you can set things up to just turn off the backing pumps when there's little gas load. That's what I do here, but with my piston (dry, teflon piston rings and diaphragm) backing pumps, don't need the valve. I have it set so it watches the power drain on the turbo and cycles the backing pump when it gets high, which saves tons of power and wear - a huge fat factor on both - the backing pumps run very low duty cycle in that mode and let me keep the system "down" all the time, even on solar power off-grid. The turbo doesn't draw squat (about 30w) most of the time.

Argon is somewhat better than N2, though slightly more expensive, and when I'm going to open the door on my system, I have it blasting into the rest like I was welding or something - lots of CFM. Like John says, it really saves time on the next pumpdown to keep that lousy wet shop air off things - even a couple minutes of that costs hours of pumping later. Haven't tried this, but I'd bet even running a really good dehumidifier in the shop prior to bringing the thing up to STP would probably help some.

Almost anything that puts energy into the tank helps with the water. Plasma is one of the best, but stab-in heaters run hot enough to make significant UV also help, by disassociating the water into more-pumpable H2 and O2...heat is a weak 3rd option in my experience (and you can only take it so far if there are any non-metal parts), and prevention rules over all.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: My new setup

Postby Jerry » Sun Jun 22, 2014 2:44 am

Lots of on/off cycles will kill capacitor start motors like these over time. I am planning on putting a PLC on the system to control valve interlocking and also to control the new gate valve. Ill just use a capacitance manometer or a convention gauge I have and tie it into an analog on on the PLC I have and then send a analog signal to the VFD on the roots blower. Osaka vacuum says I can stand up to 2 torr of fore line pressure so I can have it come up to full speed somewhere below that.

I got an old mitsubishi PLC from work with lots and lots of IO, I do need to get an analog card for it though, they do pop up on ebay. I also have a couple serial modules for it to control the gate valve. The gate valve controller has a serial interface to control it. The controller connects to a capacitance manometer on the chamber and it will actively control the gate valve to regulate the pressure in the system. You send a simple serial command to the controller to set the pressure and the controller does the rest of the work.
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Re: My new setup

Postby Doug Coulter » Fri Jun 27, 2014 7:39 pm

Yeah, I guess the switch on a cap-start motor to remove the cap at speed has a bit of an arc and that eventually kills it. Hmmm...maybe someone can think of a better way than just "bang bang" the contacts (add a triac or something?). I'm about to have the same issue with the little pfeiffer 55 l/s turbo pumps and some cap-start oil forepumps myself. My current main setup uses a conveyer belt drive for the mech pump (no kidding, slow graceful startup and so forth) which I can safely just switch with a solid state relay, no issues. Only depending on where in the pump cycle it stops, it might start up and run again to find a leak-free stopped place (there isn't a foreline valve for this mode). But then it only cycles about once an hour, if that, anyway. I suspect a non-drag turbo and oil pump would cycle a lot more often no matter what.

I'd planned a resevoir for that - let the forepump bring that down and only turn it back on if the resevoir goes above X pressure. That way it would have to run a lot less. The particular forepumps I have contain really thick oil and don't backstream at all, as far as I can tell. I sealed a canning jar over one (happened to just fit a QF gasket) and it stayed stuck on there for months.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: My new setup

Postby Jerry » Sat Jun 28, 2014 12:31 am

Also lots of on/off operations can overheat the motor. Looks like the new roots blowers come with VFDs standard now.
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Re: My new setup

Postby Doug Coulter » Sat Jun 28, 2014 6:30 pm

Well, I can't see an overheat problem unless you've got a major leak or deliberate flow. Once an hour isn't going to do it. I did it, after all, to save power on the off-grid solar system, and heat == power.

The big problem with the VFD on the one I've got - the ramp up time is so slow, and the other time constants so long, that the thing runs around 30 sec-1 minute when the first revolutionor two gets the job done. That's certainly peculiar to my setup here, but hey - they knew (or should have) when they designed the pump it was going to be the case. It's a positive displacement piston pump in two stages, after all. Zero clearance - the piston top (rubber...) touches the cylinder head. It's kinda cool machining the lets it all be that "tight". No oil anywhere, either.

I thought it was going to need a rebuild after around a few K hours of running. Well, it did start to act wrong, and I was glad I'd bought a rebuild kit along with it. Well, when I pulled the heads off, it turned out that just a tiny amount of dust that had somehow made it through the turbo-drag was affecting the piston/head clearance just enough to make it crummy. Just wiping that off and putting it back together - like new.

It takes an hour of hard work to get that massive motor hot, in my case. That would be moving a lot of gas across a big differential pressure. That's not the norm here - we sometimes pump down from atmosphere, and the first few minutes it's working really hard. But after that? Nah. I do keep the system as clean as I can, and most often it's left at base pressure, not wet shop "STP", which means that after some internal mod, it comes back down to "turbo is pumping but not much and not needing a forepump running" really quick - as in, once the turbo gets to speed and it drops the forepump, it runs a little more often than usual that first day. Then, back to a few times a day. It's really cool in all senses of the word.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: My new setup

Postby Jerry » Sat Jul 19, 2014 9:31 pm

​I have mostly finished the pass bank for the filament controller. It is separated into three banks, two 100A channels and one 400A channel. The two smaller channels got away with 1 big mosfet each, the 400A channel us using 4 APT20M11JLL mosfets in parallel. I am hoping the will be happy together. They have a very low on resistance (.011 ohm) so they ought to share current nicely.
Drilling holes in the heat sink:

ImageEvaporator controller passbank by macona, on Flickr

Mosfets and standoffs in place:

ImageEvaporator controller passbank by macona, on Flickr

Copper bus bars and fuses in place:
ImageEvaporator controller passbank by macona, on Flickr
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