I have before me a nearly identical pair of old turbomolecular pumps which I purchased on Ebay (thanks to Andrew Seltzman for pointing them out!) and collected this weekend. These things are massive; I think each one weighs about as much as I do. Needless to say, they are very difficult to move anywhere. I'll put some photographs up when I get a chance.
The rated pumping speed on these machines is 260 liters/sec, and each is driven via a belt by an external 1/2 HP, 240VAC 3-phase motor. I've bought a 3-phase AC drive on Ebay (for ~$25) which will give me programmable acceleration/deceleration rates and run speeds, fault detection, and 100 manual pages' worth of bells and whistles to play with. I can't wait to see and hear one of these machines spin up for the first time, but that will have to wait until I have space to build a proper test rig. In the mean time, I have a question regarding vacuum "throttling".
Ideally I'd like to mate the pump to my chamber as directly as possible for the sake of vacuum conductivity. It seems to be the consensus that one should place something like a butterfly valve between a diffusion/turbo pump and the chamber in order to avoid wasting precious D2 during a fusion run. However, as long as I have control over the rotor speed, could I not simply adjust the speed of the turbine to reach a comfortable pumping speed? As always, all insight and advice is greatly appreciated.
Monster turbomolecular pumps (Welch 3102)
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Greg Courville
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Carl Willis
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Re: Monster turbomolecular pumps (Welch 3102)
Hi Greg,
A valve would be the best thing to do, no doubt about that.
260 l / s is literally hundreds of times the capacity you need for pumping a continuous-flow fusor (that is, without egregious waste of gas as you have said and without loading down the pump rotor excessively with gas). I'm not sure you could even expect to slow the pump down enough to do this reliably without, at the least, placing some kind of restricting element in the throat of the pump. Another issue depends on the pump construction and is an issue that I can only mention as a non-user of your kind of pump. In a turbopump the shaft has a lot of momentum and meets little resistance, and the ability to throttle the pump with shaft speed may be precluded by long delay times while waiting for the pump to change speed (again, this depends on how mechanical power is transmitted to the shaft of your pumps).
My previous fusor ran on a little Varian baby turbo which had a nominal speed in the 50 l / s range. This was waaay too much, so I used a 4-foot long QF25 hose that cut the speed back into the 4 l / s range for deuterium. Then I could achieve good control using needle leak valves for the deuterium and an inexpensive QF25 bellows-valve right at the fusor as a vacuum throttle. The fusor's base pressure on this arrangement was down in the 3E-6 torr range, and during operation at ~ 20 mtorr, throughput was about 3 sccm of deuterium or lower, adjustable with the throttle and the needle valves. This is how you get your D2 bottle to last months or years like it should.
-Carl
A valve would be the best thing to do, no doubt about that.
260 l / s is literally hundreds of times the capacity you need for pumping a continuous-flow fusor (that is, without egregious waste of gas as you have said and without loading down the pump rotor excessively with gas). I'm not sure you could even expect to slow the pump down enough to do this reliably without, at the least, placing some kind of restricting element in the throat of the pump. Another issue depends on the pump construction and is an issue that I can only mention as a non-user of your kind of pump. In a turbopump the shaft has a lot of momentum and meets little resistance, and the ability to throttle the pump with shaft speed may be precluded by long delay times while waiting for the pump to change speed (again, this depends on how mechanical power is transmitted to the shaft of your pumps).
My previous fusor ran on a little Varian baby turbo which had a nominal speed in the 50 l / s range. This was waaay too much, so I used a 4-foot long QF25 hose that cut the speed back into the 4 l / s range for deuterium. Then I could achieve good control using needle leak valves for the deuterium and an inexpensive QF25 bellows-valve right at the fusor as a vacuum throttle. The fusor's base pressure on this arrangement was down in the 3E-6 torr range, and during operation at ~ 20 mtorr, throughput was about 3 sccm of deuterium or lower, adjustable with the throttle and the needle valves. This is how you get your D2 bottle to last months or years like it should.
-Carl
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Richard Hull
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Re: Monster turbomolecular pumps (Welch 3102)
Wow! A couple of cases of too much conductance/pump speed! Virtually unheard of, but I guess in the world of surplus you use what you have and choke off the big pumps that you pickup for a song.
One for the record books, I guess.
Richard Hull
One for the record books, I guess.
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Greg Courville
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Re: Monster turbomolecular pumps (Welch 3102)
Well, fortunately the motor drive I've purchased will in theory allow me to operate the motor at as low as 0.5Hz (which translates to 30RPM at the motor shaft, and probably about 90RPM after the belt and gearbox), and supports variable-rate electromagnetic braking and a mess of other features, so slowing the rotors down shouldn't be too much of a problem as long as I'm gentle and don't cause the motor to exert such a force as to slip or break the belt. However, you did bring up a good point. There really is no need for a 260l/s pumping speed, except to quicken the initial pump down, and I don't mind waiting a few extra minutes if it means less waste and better control. Thus, perhaps the best path is to combine the two strategies -- connect the chamber via a steel flex tube (which also simplifies mounting by a great deal!) and a small bellows or butterfly valve to limit and control over gas flow, but also run the turbo at reduced speed (perhaps ~50%) when its full capacity is not needed, in order to reduce power consumption, noise, and maybe pump wear...
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Tom Dressel
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Re: Monster turbomolecular pumps (Welch 3102)
When I bought my Hummer V, which is a sputtering rig , it came with a Pfeiffer Balsers TPU 040 turbo. It had a copper blank gasket in the 2.75 CF throat. The blank gasket had a 1/4 inch hole drilled in it to limit the through put.
Before shelling out for a buterfly valve you might try a static restrictor plate between the turbo and the chamber.
Tom Dressel
Before shelling out for a buterfly valve you might try a static restrictor plate between the turbo and the chamber.
Tom Dressel